Circuits FAQ

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Tuesday, December 08, 2015

Digital Counter - 4029 and 4511

I just about the circuit you made. what kind of IC is 4029N & 4511N? Is it a diver/decoder? I tried to research on the datasheet but it cannot give exact specification...

Mail from JT from Philippines

4029 is a Preset Dec-hex, up-dn, Counter - and 4511 is a 7-Segment Display decoder. Learn more see .
Ssend a jpeg photo or rtf or pdf. please also tell me which page or circuit is this question about. any other doubts feel free to ask.

 Is it this ... Simple Digital Counter - doc00021

Digital Counter4029 and 4511


yes, .thanx for the links..i'll try to go over with the where can we purchase those items if ever we need it?

Reply from JT

It depends on which country you are in,... see this page Components Materials


Thursday, December 03, 2015

Lead Acid Batteries FAQ

Some Questions, Searches about Batteries Answers Below, My Collection of Website Resources.


The Lead Acid Batteries are used in Automobiles and UPS - Uninterrupted Power Supplies. Battery Banks and Arrays are used in Home and Industrial Power Systems with Solar and Wind power charging too.

Chargers & Charging -- Battery Management

These batteries have survived many other types, for rugged high power usage, even beyond 100Kva. It is all the more important for us, to learn how to use them properly. Intelligent charge controllers and charge-discharge cycle regulating managers, will ensure a long lifespan for optimum cost-effective usage of this Electro-Chemical Wonder.

Comparing marine batteries Gel, Absorbed Glass Mat (AGM), flooded lead acid

"While I was on a month long assignment in Washington DC in 1999, I read an article on battery management in the 1999 Ocean Navigator "Annual" issue that I thought was deeply flawed. The contributor, Chuck Husick, illustrated how he thought one should maintain and configure a marine battery system."
 Shown above is a Sealed Lead Acid Batter from Power Sonic Corporation (Europe)

Wednesday, December 02, 2015

Power Oscillator Circuit Design

I am trying to find a circuit diagram for a long time, which will give me the o/p Characteristics as 12V, 0.5A & 4000 Hz (or variable frequency). Will you please help me in this regard? I will be very very thankful to you.

Mail from PS

First make an Oscillator and then Power Amplify it.

LM675 Power Operational Amplifier

"The LM675 is capable of delivering output currents in excess of 3 amps, operating at supply voltages of up to 60V. The device overload protection consists of both internal current limiting and thermal shutdown. The amplifier is also internally compensated for gains of 10 or greater. "

Op Amp Booster Designs  PDF

"The design of booster stages which achieve power gain while maintaining good dynamic performance is a difficult challenge. The circuitry for boosters will change with the application’s requirements, which can be very diverse. A typical current gain stage is shown in Figure 1."

Op Amp Booster Designs

12V, 0.5A & 4000 Hz (or variable frequency) is possible, very high frequencies difficult, for that you have to study RF behavior. Experiment from DC to 1 M Hz, no more with these circuits. 200/300 K Hz if you manage you learn't something. Study pages, learn and try to build it yourself. These links are for learning.


I am extremely thankful to you for your precious reply for my mail. I have tried it to complete the circuit as per your suggestion, but the results are not as per the requirements. Here, I tell you the exact situation. Sir, I am working on the efficiency improvement of an alternator. for this reason I need a frequency generator circuit which will give me the o/p characteristics as 12V, 0.5A & variable frequency upto 4000Hz. The signal must be AC sine waveform. It can be applicable to inductive load. The i/p will be simply 230V AC. Will you please design a circuit for such requirements?

I am in great need of this. Please, I request you to design it. I will be very very thankful to you.

Reply from from PS IN

For professional service, there will be design charge. Your reply will be posted. Anyone who can design this can comment here.

Unique IC Buffer Enhances Op Amp Designs, Tames Fast Amplifiers

A unity gain IC power buffer that uses NPN output transistors while avoiding the usual problems of quasi-complementary designs is described. F


Sunday, November 08, 2015

Eng-Tips Forums - Electrical and Electronic

These pages will probably help you do a design review of your new circuit or even answer a doubt in your product design. Use the Search.

Eng-Tips Forums - Electrical and Electronic

Eng-Tips Forums - Electrical and Electronic

  • Electric power engineering
  • Electric motors & motor controls engineering
  • Electrical/Electronic engineering other topics
  • Circuit Design
  • Programmable Logic Controllers (PLC)
  • Communication & Signal Processing engineering
  • Antenna & Propagation engineering

Saturday, November 07, 2015

Ship Automation and PLC Technology

A Mail Thread from 2008, has been posted here. This is to enable students and engineers understand : The needs in in Maintenance Automation or Marine/Ship Automation. I could not take up this task as my engineering designs are only on paper, I used to take up automation projects, a decade back, not anymore. This feedback is also to enable product designers to create a ready configurable solution for Maintenance Personnel..

I would like to suggest that - A Simple Configurable (No Programming Knowledge, Graphical Drag-Drop more like an iPhone app) Automation Solution is required with a Magic Control Box with I/O. Affordable, Limited Functions. Where budget is squeezed and a temporary solution is needed. Even as a emergency standby solution.


Ship Automation and PLC Technology

I am a Marine Engineer originally from ....., now residing in Australia. I am looking to modify a system that has 24V DC input to control 24DC solenoid valves and would like to go via solid state relays. The control inputs for the solenoid valves inputs are via 2 Kohm joystick potentiometers having -12V to 0 to +12V having a centre tap. Any thing you can tell me about how I can do this?

Mail from BD of AU

Do you need time proportional control of solenoids, or just on-off. If it is a Analog control from a linear Joystick, it is complex. If it just on-off solenoids on movement of joystick it is simple. use comparators to detect levels from joystick. the output of comparators go to a driver chip. The driver chip turns SSR on-off. Use an SSR which can handle the Solenoid current.


The original is analogue input signal from joysticks into a Siemens S5 PLC and digital output to solenoids. The Analogue modules have inputs from both jthe oysticks and feedback potentiometers. I would like to mimic this if possible and do away with the the PLC altogether and could look at other easier options. Can you provide any advice? How much would something like this cost? Much appreciate your help.

Mail from BD of AU

You could see this article from siemens SIMATIC S5-S7 Migration Support. This is a PLC, means an embedded system, it has a microcontroller and firmware. Users can program it with Visual Design aids like Ladder Logic on a PC Interface. The PLC then will work as a stand-alone unit, to manage a machine or process automation.

You can use another PLC to replace the existing system, Programming a PLC is very easy with the software that comes with it. A custom embedded solution is possible only after understanding the entire process on which this PLC was used. Which is not just the PLC and Electrical Components but the process control logic and learning that goes inside. A custom solution may be expensive if it is just for one machine or process.

Are you going to use it in a OEM kind of application for manufacturing of some industrial systems? Then a custom solution is feasible, as the cost is amortized over the many control units that are made. If it is repair and maintenance then just use the SIMATIC upgrade instructions above. Siemens Australia & New Zealand 


....... We are only looking to drive a winch on our ship which is basically controlled by a set of 22 solenoid valves in differnet configurations. The S5 PLC we have is 22 years old and don't really see the point of migrating to S7 at the cost for what we need to be able to do as the ship is so old already. At any one time only maybe 3 or 4 are energised so basically quite simple so I can't see why we need a PLC at all. I'm sure that if I gave you all the information you could tell me how to do it in a matter of minutes. .... .... ..... as knowledgeable as you are with these systems but believe we don't need a PLC at all. Any help you can give me in setting up a system to control 6 sets of solenoid valves from 2 joysticks.

In one mode each joystick operates 3 individual solenoid valves each In another 1 joystick operates all the valve while the 2nd joystick is disabled. Other 16 solenoids are mostly operated by individual On / Off switches. Must be quite obviously simple to do this for you, so any help will be much appreciated.

Mail from BD of AU

Much as i would like, i would not like to take up such work now.

I think a person who can make a cost effective solution is This firm in australia may make a nice solution

Contact me for anything you need to know, i would still insist that a PLC is better. We cant take any chances with ships, it is a risk, make a robust solution.


Thursday, October 22, 2015

PC Sound Card Oscilloscope

Dear DAPJ: I would like to buy a Microphone and either #1. an oscilloscope or #2. sound oscilloscope software. For hobby purposes, I would like to sample different sounds & view the various sound waves studying the amplitudes & frequencies. Do you have a product that would meet these criteria?

Thank you. Respectfully,

Mail from MH - US

No i dont sell anything. But here are a few suggestions.

OsciPrime is an Open Source Android high speed data acquisition hardware platform and Android oscilloscope application. (2015)

Simple solution for only sound - Zelscope buy only software. Test out out, buy if you like it. You need a computer.

Buy a PicoScope or if you want to build one Bitscope

Study also
delabs (2009)

Wednesday, October 07, 2015

Usage of Schmitt trigger NAND Gates

I have a question about your "Long Duration Timer" circuit, del20017 found here ..Long Duration Timer Clock

Long Duration Timer

You have labeled U1 as a 4093. A 4093 is a NAND with schmitt trigger inputs, yet the schematic displays only NAND gates without schmitt trigger inputs. Which device did you intend? A 4093 or a 4011 (Quad 2 input NAND gate).

Mail from PB

Where mixed signals are at input both analog and digital 4093 is better. Like digital inputs after going thru a long cable the square wave gets deformed, 4093 refines it to a digital square again. When interfacing with input devices like switches 4093 is better as it works as a noise filter. Generally 4093(++) is an upgrade to 4011, i think it is a pin to pin replacement .

Digital Timers Counters and Clocks

In the circuit above U1C and U1D have to be schmitt trigger nands. U1B also needs a bit of wave cleaning. U1A can be 4011.


The 4093 gate didn't embed properly .. so I have attached it this time. thankyou for your prompt reply. I understand the need for schmitt triggered inputs as you have pointed out. I guess for completeness I was also pointing out that the schematic should show the NAND gates with schmitt triggers as shown below.

2 input NAND with schmitt trigger 4093.

Reply from PB

Sunday, October 04, 2015

How bently nevada proximity sensor works

A mail thread from my mail box, i was answering a question by an engineer about proximity switches. Question was -  how bently nevada proximity sensor works

Mail from UM

Microwave and RF radiates energy. - You know when a magnet is moved near small nails it make them Move ! If you make an DC electromagnet, it make the nails move again.

How bently nevada proximity sensor works

But when you keep swapping the polarities, That is with an AC supply it generates a field or radiates an energy. Right from the Toy generator with magnets to the Sun it is the same. The highest form of sun is it radiates photons.

RF is nothing but a Magnet rotated at high speed which is called frequency. This energy can cause food to cook in your microwave oven or a proximity sensor to gauge the gap. It even helps people when the have a sun bath.

I have seen even an old Analog Joystick of a Machine has this induction method to position objects. Study Links below for helping you understand better.


Applications of electromagnetic induction - An eddy current is a swirling current set up in a conductor in response to a ... and to provide the necessary energy required for the motor to do work.

Design of an Eddy-Current Proximity Sensor using a Two-Coil Planar ... .However these proximity sensors are not conducive to scaling to conventional integrated circuit levels. This is because most conventional eddy current


Sunday, September 13, 2015

Dynamic Digital Tutors

Date: Wed, 30 May 2007 17:00:46 -0400   - Subject: 555 simulator


I just found and had a chance to play with the 555 simulator over the internet. As I do a lot of designing and use the 555 in many of my projects, this tester is a really handy tool.

Is there a way to get a copy of this simulator that will simply run on Windows? If not, how about running it through Internet Explorer?

I realize I could simply put a link to your site and use it that way, but I don't always have a connection to the internet. Basically, I would just like to use this little applet on my laptop on my bench at home.

Thanks for your help, and congratulations on such a cool program.

Mail from DN Canada

I am happy you found my gadgets fun to use. ,

555 Oscillator and Decade Counter -Red Button Powers LED Running Lights, Adjust R2, Move Mouse over the Images.

Astable Multivibrator with 555 - Red Button Powers, Move Mouse over objects to know.

Preset Digital BCD Counter - Move Mouse over the Images, Tool Tips will Tell All.

Dynamic Digital Tutors

In the links above, you will find a code to add to your webpage or blog. I have sent you a gmail invite get a gmail then use that login to open a account.

You ought to have a blog, these gadgets (code) can be added to your own blog, then you can refer it at your own pages. You can then share your learning with your friends too.

If you still want you use it offline let me know, i will make a zip and send it to use without internet. Have you tried using a Wireless LAN.

Wireless LAN - Wiki- A wireless LAN or WLAN is a wireless local area network, which is the linking of two or more computers without using wires. WLAN utilizes spread-spectrum or ..

Then lastly ... check these freeware you can download for 555

555 Timer PRO provides an array of design wizards, circuit blocks and information panels that facilitate the use of the 555 timer. Component value calculations for the 555 take into account the supply voltage, timer fabrication (CMOS or Bipolar), and, where appropriate, load currents.
(use the freeware version)

555 Timer Project Design Software for Beginners and Experts

Let me know if you need anything more.


Hello again,

Thanks for your quick reply. As I don't have a website nor a blog, I was hoping that the 555 program could be just a stand-alone application. Is this possible?

Your program is really nice, so I hope it can run as a small program by itself.

Reply from DN

Here is a file that will work in your laptop without internet. Can you please verify if all the three work well. digital-tutor.chm - right click - save as - to a folder of your chose and then open it (removed)

Please check both online and laptop without internet. Your feedback will be useful to me so that i can correct or improve.


See the Complete - 555 Timer at EEMetric

Wednesday, September 09, 2015

Insulation Resistance Analyzer Required

Please quote for Insulation Resistance Analyzer DRT101

from AT 

delabs is a website for education of engineers and hobbyists . The photos and documents are products that i used to make years back. I do not manufacture now. The circuits and photos are to give ideas for youngsters and entrepreneurs.

Insulation Tester and Tera-Ohm Meter with Polarization Index
One of the Products i made and marketed in the Eighties.

Insulation Tester and Tera-Ohm Meter with Polarization Index


Sunday, September 06, 2015

Polarized Capacitors and 555


This circuit of yours is EXACTLY what I was looking for. TOTALLY cool! However, I have a few questions about it...mostly because I'm a software guy. Astable 555 Timer Flasher

So please bear with me if these questions sound stupid...

1) I want a 50us on / 280 us off (3000 khz ish with at 15% duty cycle) circuit. THis means that Ct needs to be about 7000pf. Unfortunately, you can't get 7000pf caps polarized. Does Ct REALLY need to be polarized?

2) Also, what does a polarized capacitor do that an unpolarized one can't? Could I just stick a diode on it to make it polarized?

Polarized Capacitors and 555

3) THere's a bubble on pin 4 (the reset pin) on the 555. Does that mean I need an inverter? Would a 74HC04 do the trick, or is there an easier way to do that (I need the HC because I have 6v Vcc)

4) I just want the output signal...can I drop all the LED and battery stuff to the right without affecting the circuit?

Mail from GK

1) A cap being polarized is due to manufacturing. Only Electrolytic Caps including tantalum caps and others that are polarized give you high capacitance. If you do it with just a plastic, mica or paper separator (dielectric) then you get very low capacitance. So they have to wrap or coil many meters of two-metal-films and a insulator like plastic sandwiched to get upto 10uF or even more. These are non-polar and will become very big for say 100uF. Hence we have the electrolytic caps with high uF for the PCB real-estate they occupy.

UnPolarized are ideal and can be used anywhere. Use Polarized caps where the footprint area you need is less for a certain value of cap.

So you choose caps based on space, cost, AC-DC, purpose. Thumb-Rule 1uF and above only el-caps. Unless you need it in a AC circuit or high voltage like 1 Kilovolts where polyester caps are used. 7000pf or 7nF is available as ceramic, mica, plastic, paper. use what you get right now. Making 7nF el-caps was never required. 1uF and Above el-caps.

2) Being a polarized cap is an handicap. So you dont need to polarize a unpolarized cap, so just leave it alone, it is fine as it is.

3) The bubble says "I pin 4 of 555 have a inverter inside the 555".

4) You can drop the LEDs, but you have to power the circuit with a batt or mains-DC-9V-adapter.


Thanks for the response! So I don't need a 74x04 chip to go into the reset pin? Cool. I'll stick to the non-polarized cap and and a direct input into the 555 pin 4. The board I'm using is powered by 6v, I hope this will do the trick, don't want to go the rectifier route.

Reply from GK

"When you build projects Software and Hardware, design products and services that are useful to society" - Solderman 1709

Tuesday, June 16, 2015

Significance of Current Loop 4 to 20 mA Standard

Subject: delabs comments - Tell Me. message: why 4-20mA standard. why not 2-22mA or any thing else

Mail from MU

they knew you would come up with a question like this. so see this page 4-20mA Current Loop Primer and also Intrinsic Safety Circuit Design.

...transmitting 0mV or 0mA will be lost in the noise too. 4mA is enough power to go over long wires with low error due to leakages. and current ensures RFI-EMI immunity as the picked noise does not have any juice just some voltage.

4-20mA helps in Noise Immunity, Providing Power for efficient signal conditioning circuits making two wire transmitters possible.

See more at my pages Industrial Process Control Circuits

Significance of Current Loop 4 to 20 mA Standard

Hence it could be 4-20mA not mV. 0-20mA is not good enough, but is used when you just have to interface two cards or instruments close by. 4-20 mA can go from your street to the next or even much more depending on cables and voltage.


Thursday, June 11, 2015

Optical switch with photo sensors

Can you help me to find circuits which uses photo-sensors.and if you do have them, would you please send them to me.

Mail from TM

Just a few days back i have added one. It is to turn of-on water taps.

Optical Obstacle Switch. - one more here  thru all links in great detail.

Here is an image of a low cost gizmo that applies the photo-sensors to detect motion. They are called motion detectors.

Optical switch with photo sensors

How Infrared motion detector components work - Infrared radiation exists in the electromagnetic spectrum at a wavelength that is longer than visible light. It cannot be seen but it can be detected.

K30 PIR Movement Detector -  This circuit is designed around a custom motion-detection IC KC778B. The circuit utilizes both a PIR (Passive InfraRed) detector and a light-dependent resistor (LDR) to detect motion up to 6 meters away.

PIR Controller – KC778B

The MPCC has been designed for easy implementation of AC control functions that use a Passive Infra-Red (PIR) motion detector. Due to its high sensitivity and reliability, it is also widely used in security product.

PIR Controller -KC778B - Auto Camp Light

Above is an example of  camp light using the KC778B. Uses battery 12VDC. Internal voltage regulator is used,  but can work down to 7V.


Another related Question

I am working on a project where I am trying to adjust the brightness of a set of LEDs based on the amount of IR light detected.  I have experimented with using a photo transistor, but i can't seem to amplify the difference experienced enough to visibly change the brightness of attached leds.

Lighting and Power control Automation

i am researching for a project for industrial automation . in this i am having one concept that is following below

if any one of person is in room the electrical power should be connected in this time one or more persons are entering in side that room at that time also that power should be ON .Now that persons who are all inside that room one by one is coming out that power should not be OFF but the last person who is coming out side off the room that power should be OFF

this is my concept of my project for this concept please design a circuit for me please send me replay for this concept

Mail from TM

You have to count people with optical switches or infrared detectors. Then using dsp or up processors and figure how best to establish number of people in room.

See below Motion Detectors - Professional and a DIY Version

Motion Detectors - Professional and a DIY Version

See a Related circuit here Optical Obstacle Switch.

A pair of optical switch-sets for every door that leads to room. Only if object cuts both beams then you count one. It is the idea you have to develop, Circuits are on the web.

See also - InfraRed Detector for Proximity Switch and InfraRed LED Flasher for Optical Switch

A pair of optical switch-sets for every door that leads to room. Only  if  object cuts  both  beams   then you  count  one. Even windows need sensors, if you expect some to use that for movement.  But some may slip in between beams, you might  have  see that happen.

Motion detector - Wiki

An electronic motion detector contains an optical, microwave, or acoustic sensor, and in many cases a transmitter for illumination. However, a passive sensor only senses a signal emitted by the moving object itself.

Other methods are RFID fixed on every person. Then it may be foolproof. Also as  most have cellphones, track the phones with GPS and count people in room.  A footrug with a weight measurement can also count people moving thru door. But a few may jump over them, so it has to be foolproof log footrug.

Updated - 10th Jun 2015

Saturday, May 16, 2015

Power Supply Regulators and MOSFET Transistor

HELLO THERE ...COULD anybody pls help me with a place to get more information on the following components...cant seem to find it anywhere.

W20NB50 W8NB100 found them in a liteon power supply pack for a database supply. i just don't know what they stand for. ...saw on a web page that it is produced by ST micro electronics. i went there but no show ..can somebody pls help?

post by FP

W20NB50 ST Power MOSFET Transistors TO-247 N-Ch 500 Volt 20 Amp
W8NB100 ST Power MOSFET Transistors TO-247 N-Ch 1000 Volt 8 Amp

You  will find equivalents here - NTE Electronics - N-Channel MOSFET Selector

ST’s MOSFETs with a breakdown voltage > 650 V offer low gate charge and low on-resistance down to 0.275 Ω (850 V) in PowerFLAT 8x8 HV packages.

Junction design of a Mosfet

Junction design of a Mosfet

"The source-to-body and drain-to-body junctions are the object of much attention because of three major factors: their design affects the current-voltage (I-V) characteristics of the device, lowering output resistance, and also the speed of the device through the loading effect of the junction capacitances, and finally, the component of stand-by power dissipation due to junction leakage."

Updated - July 2013


Thursday, May 14, 2015

uC Board is Buggy on Brown Out

I'm working on a project which involves battery  Ni-Mh 4x1.2v, 2100mAh], which power-ups the boards. The current consumption is about 150mA. Now what I wish to do is disconect the load when my battery voltage falls down to 4v or so

Because now when my battery reaches this voltage the instrument fails to work, sometimes my program gets corrupted. And battery reaches a critical voltage level like 1-1.2(summation of all 4 batt). what else can I do so prevent this?

Mail from MO

Depending on your budget you can solve this, a watchdog and power management chip from maxim may work for these types of problems.

You can even build your own watchdog and power management with logic and comparators.

When the uP malfunctions it has to be reset by a watchdog timer which monitors if the uP or uC is pulsing in the way expected.

Battery Backup for SRAM or Microcontroller

And when the power goes down slowly like a Brown out, you have to save all RAM on a Flash chip and shutdown system and wait. Or have another backup for RAM and use a low power RAM. Make sure that you write a start sequence and shutdown code in your program.

When you start start with a clear ram ( if not batt backed up) then load values from flash. Make sure power up, power down resets are ok.

Digital to Analog Converter with uC Watchdog

Internal comparators implement undervoltage/overvoltage warnings and windowed-reset functions.

Supervisory Circuits Keep Your Microprocessor Under Control


Supervisory Circuits Keep Your Microprocessor Under Control

"Understand the value of a µP supervisor to ensure proper system operation during power-up, power-down, and brownout situations (undervoltage monitoring). In addition, provides information about overvoltage and windowed monitoring. Describes additional features such as manual reset, watchdog timer, battery backup, and chip enable gating. Discusses the need for multi-voltage monitoring."

In an industrial environment your card it may malfunction due to EMI RFI. If your Board controls a huge Motor, when motor starts your Board could hang or Boot. You have to study and work out a solution.

The circuit or code is not everything, it is the Engineering that matters.


Monday, April 06, 2015

Using LEDs with Battery Power

What are LEDs ? How can we use them for Long Battery Life

Mail from AD

If LED flashes at 5-10 K Hz at even 50% Duty Cycle. It may save some power and improve life. So it is just an idea, it may not solve the problem. The idea was to improve battery life and give uniform light for annunciators. It may not be good for flashlights.

Light-emitting diode - Wiki

Light-emitting diode - Wiki

LEDs have many advantages over incandescent light sources including lower energy consumption, longer lifetime, improved physical robustness, smaller size, and faster switching.

The LED Museum

The LED (and Laser) Museum. A site devoted to testing & reviews of LEDs & LED flashlights in all common chemistries.

LEDs and OLEDs
Small lights with big potential: light emitting diodes & organic light emitting diodes.

Light Sources in Electronics
Light can be produced and/or controlled electronically in a number of ways. In light emitting diodes (LEDs), light is produced by a solid state process called electroluminescence.

Using LEDs with Battery Power


Monday, March 16, 2015

Digital Programmable Gain Amplifier

I read your post which is about, Digital gain control of Op-amp.  I have some questions to ask, if possible.  Please reply ASAP.

Precision Amplifier with Digital Control  (only for DC and low audio frequency)

Mail from KAM of UAE

Reply by delabs - Ask, i will try to reply.

I am student and I have a lab project to work on. It is about a digitally controlled variable gain amplifier. So, is your post relates to my topic. If you know a simple way of design, help me please. I will appreciate it.


See these links and tell me if this is what you are looking for. These are for Communications.

LMH6517 Digital Controlled Variable Gain Amplifier Evaluation Board

LMH6517 Digital Controlled Variable Gain Amplifier Evaluation Board

The LMH6517EVAL evaluation board is designed to aid in the characterization of TI`s High Speed LMH6517 Digital Controlled Variable Gain Amplifier

MAX2027 IF Digitally Controlled Variable-Gain Amplifier

The MAX2027 high-performance, digitally controlled variable-gain amplifier is designed for use from 50MHz to 400MHz.

The circuit i have on my site  is for low frequency and DC. used in instruments.  What you may need is for RF.  What is the Application DC, AC, or RF ?

Reply by delabs

My input is an AC signal, and I want to have changeable gains, I mean that one time the gain should  be 50,  100, 150, and 200.  However, this changeable gain should be controlled by digital inputs.  So, I think this is what the circuit do.


Gain of 200 means you may need more than one stage of amplification.The circuit of mine can be used for DC and Lower Audio Frequencies.  

If you go above 2K Hz the Slew Rate and The bandwidth of the Amp IC must be chosen carefully. These are the areas you have to study and choose. Then this circuit with fast opamps can cover Audio Frequency. 

At each stage you must study the Bandwidth response and plot a curve and use compensating caps if required. In case you want a uniform gain over a wide range over a wide range 

TDA9901 Digital programmable gain amplifier

If this is for a Very Wide bandwidth measuring instrument, it is very difficult. You may have to use special low capacitance switching elements. I can only give you ideas and links, i cannot design a circuit for you. You have to figure that out, that is how you learn. Use the internet more and study the circuits and concepts and ask me the doubts you have.

Reply by delabs

I really do not want you to design it for me. I want to learn.  The good news is that is i manage to design everything, but, I got confused when it comes to control the variable gain amplifier digitally.  I tried to use decoder and multiplexer, but, it does not work.  Can you give me some advice.  Sorry for annoying you, and thank you for your gentle help.


See this

LTC6910 - Digitally Controlled Programmable Gain Amplifiers

The LTC6910 family are low noise digitally programmable gain amplifiers (PGAs) that are easy to use and occupy very little PC board space.

Low Noise AC Amplifier with Programmable Gain and Bandwidth

Two LTC6910 programmable gain amplifiers can be combined to provide independent gain and bandwidth control using two 3 bit digital words. The Gain Control PGA simply varies the circuit gain from 1 to 100. T

Friday, March 13, 2015

Blind Temperature Controller

message: from SJ

for my hobby purpose (pewter small models) i 'm building a kind off rubber press with two hot plate about max: 200degre C. i found your website and studied the different circuits concerning J, K thermocouples, and proportional control that will suits my needs.

I would need more information about one :

- Is the circuit called Blind controller designed for J thermocouple ? as not specified, is not what component value should be adapted?.

- what is function of pot 1K RKE 1W ?

-what does mean RTD i couldn't figure out...?

- Is it possible to use at end of the controller an IC type MOC3041 after Q1 to have zero voltage switching and if so what components should be adapted or add\ removed?

my knowledge in the field are limited question could appear simple... Thanks for understanding

Mail from SJ

In this page Industrial Process Control Circuits

There is a circuit blind proportional temperature controller That is probably what you are referring to.

Blind Temperature Controller
It is for J Thermocouple you can calibrate it with boiling water and Ice. Or if you have the millivolt source you can calibrate it with that.

The 1K RKE 1W is the Dial Potentiometer, You have to fix a dial and Knob. Calibrate the Dial with markings of temperature.

RTD is not for this circuit. Unless you want to use it. A 1mA Source is shown in circuit for an 100 ohm RTD sensor.If you are using J type Thermocouple then that is not required.

RTD is more precise, but may be a bit expensive.

MOC3041 can be used, circuit is here. SSR and Zero Crossing Opto-Coplers

Remove the Relay K1. Take two wires from the points that were going to K1 Coil pins 1 and 2. Or take two wires from across diode D1, Observe proper polarity or MOC3041 may go.

The other side of MOC3041 controls Triac and is high voltage and can give shock. Buy and use a SSR

SSR and Zero Crossing Opto-Coplers
Let me know if you have any other doubts.


A words to thank you for the few minutes you spent in answering my questions, " Bravo" for your web site it is particularly well designed and functional...

Yes i might have to contact you again but your explainations are crystal clear so i should not "bother" you more at least for this project.

It is still a long path for me before my project get done, as i built myself all parts of the press,but i won't forget to E-mail you a picture of the result with details.

I could have bought one already made of theses as their price is still affordable, but my opinion is in the internet spirit and lead me to : do it yourself if you can, satisfaction will be your salary. thanks again for your help,

Reply from SJ

Thursday, March 12, 2015

Mains Voltage Monitor

i need a circuit design to detect generator voltage and display with LED for certain value of voltage. for example red LED"s for voltage under 180 V, green LED for 180-220V and Yellow LED for voltage above 240 V. i would like be glad if you would like to help me design it!

mail from KB

I have some designs that may do that easily. Have a look at them. We could modify them to suit your needs.

First the 230V has to be brought down to say 2.3V with a transformer or attenuator. Then we have to measure it with LED bar graphs, choose color of LED as required. If the measurement unit is a sealed plastic box then it can be transformer less.

Look at these first. Mains Stabilizer Circuit, In DMM Circuits see ....analog and 3-1/2 digital display for +/- 199.9mV. in LM3914 you can light up a bar graph or a single LED to show the Level.

in Water Level Sensors see Fluid or Water Level Sensor using reed relays - circuit example

DPM based on ICL7107 see AC voltmeter digital, 7107, pdf After you looked at all the circuits, Tell me how i can help you.

DPM based on ICL7107


i have seen almost all the source you show me. i got more explanation and also more confusion...!
well, actually all i need is not too complicated but maybe its tricky for me. i got the idea about using voltage comparator via voltage divider, not using transformer like you said. it is more reliable and easier, isn"t? but again i got little bit trouble to design it!

is it easy for you ? i hope you will give me best solution for it! if you dont have mind i will wait for your design as comparison, but not in hurry! Ok, thank you for your kind attention!

mail from KB

I will make a circuit for you as soon as possible. Do you need just 3 LEDs or more. do you have experience in using 230V supply safely as it can give shock. give me more details if possible.


Again thank you very much for your attention on my question. actually it will be better to have 9 LEDS for 3 kinds. i have some experiences in installing 220/230 V but not expert, dont worry about that i will try as safe as possible.

i would like to install picohydro for my garden with power about 300 watt using induction generator. it will be expensive and not comparable to use complete controller as well. so i wondering to have voltage indication to estimate voltage condition, or even you have experiences with picohydro or minimum requirement for it (controlling, safety) like overvoltage protection, etc. again i will be glad for it....!
i will wait for your answers.

mail from KB

Can you please explain in brief what is picohydro and how induction generator is used. I have attached a circuit, It is not tested, It might do the job. You must have basic knowledge in building, testing and troubleshooting circuits.

After a study of the circuit you can tell me more clearly your needs.


Ok, induction machine can also used as generator if you at least:

1. Drive motor faster than synchronous speed (slip = negatif)
2. There is reactive power from outside (capacitor/Grid)
I think you know it! in my case i used 3 phase induction motor with 1 phase output only (C2C connection),its more reliable and much better than 3 phase output for small power! its easy to build! any way, thank you for your design...!i will try to study it before i build.

mail from KB

The circuits you asked for with some explanation has been published here.

Mains Voltage monitor using LM3914

Simple Mains Voltage monitor


Monday, February 16, 2015

Single Chip dual power supply

message: Hello, I want to know the single IC which can provide Both + V and -V from a single +Vin supply.. I need this for my dual supply opamp.Reply me as soon as possible. -  Thank u.

Mail from KM

There were chips, but now obsolete as most use a smps circuits. you can try this RS232C Level Converter it has -10 and +10 that can power low-power cmos opamps and chips.

or use LM7912 and LM7812l you will need two chips, there was a LM326 but not now. See Linear Regulated Dual Polarity Power Supply

When a Inverting Opamp Configuration is at a steady state, we say the Inverting Input is at a Virtual Ground. That means it is at 0V w.r.t to the dual power supply ground, but it cannot drive or draw any current. It is at a high impedance, but still at 0V. When you buffer this 0 V, you get a low signal ground for a opamp supply. Opamp generates Virtual Ground. See this a Isolated dual power supply from 5V

Dual Polarity Power Supply


I am very happy to see ur reply.I am appreciating ur job. Ok.. Ur information is most useful for me.. We ill meet with another problem.. Thank u..

Mail from KM

Thursday, February 12, 2015

Some Cyclic Timer Ideas

A product spec and need from my email archive. This indicates how clarity in customer specs can help him get a working solution with less wastage of time and money.

Electronic design assistance

I am seeking assistance from someone that would assist me in designing a custom circuit for a prototype that I am working on. I would be willing to work out a mutually lucrative contract with someone who wanted to get involved with this project.

General Circuit description

Cyclic Timer

Circuit components:

  • Tank filled with liquid.
  • Fluid hose to pump
  • Fault switch or Low level float consisting of a magnetic float encased around a tube with a no/nc reed switch.
  • Liquid 12vdc @ 5a pump
  • Trigger momentary switch to activate cycle.
  • Reset Switch.

Circuit requirements

When momentary switch(3) closes for 2 seconds, pump(2) will activate (ON) for an adjustable time from 2-3 seconds. After pump(2) has activated an adjustable timed 10-60 minute countdown of the pump (off) will begin. Any additional signals from momentary switch(3)will not interrupt this cycle. If when cycle is complete a switch closure from momentary switch(3) still exists the cycle will repeat. If at any time circuit receives a signal (NC/NO) from fault switch(1-B) cycle will be immediately shut down and not restart until manual reset switch(4) is pressed.

Notes: 3. Momentary switch to activate cycle could be in the form at current of an ultrasonic movement detector as seen here.

I have not tested this switch yet to insure that it will perform the necessary detection capabilities, so this may change if a more suitable device is located.

Notes:4 The reason for the manual reset button or circuit is that the float switch is very sensitive. The potential exists that when liquid level is low and pump activates, the amount of fluid that the pump draws to prime itself, may momentarily fool the float switch into thinking that tank has become empty. When pump shuts down and pump looses it's prime a small amount of fluid will back flow from pump back into tank causing the level to fool the fault switch into thinking it has an acceptable level. I want to avoid a toggling effect that may be created when level gets into this level of liquid.

General Notes: I have found several cyclic timers that could possibly perform the above list of requirements.

Mail from RS

Standard Solution

Similar thing here two-stage-sequential-timer at  delabs Service Project Circuits


Saturday, February 07, 2015

Thermostat with digital display for PTC1000

Thermostat with digital display, I need a electronic thermostat with a 2 digit display... Do you have anything like that??

mail from EU

can you explain how you plan to use it. then i can give you a suitable circuit. It it for a bakery oven or plastic injection moulding. do you want on-off control or proportional control. do you need a circuit and pcb or only circuit. do you want me to make a custom design for you.


Thank you very much for responding my e-mail! It´s really for may kitchen oven and I did put an on-off control but..really doesn´t work quit well so I thought in putting a proportional control or would like to have both, on-off and proportional, and see which works best.

I want to quot that it´s NOT FOR COMERCIAL USE. It´s only for only for my home. I was looking tru the internet but didnt find what I want. I would like a simple thermostat with a two digital readout probably made with OP-AMPS cause with microcontroller it´s quit difficult for me because I don´t have a programmer and, also, do not understand quit well how they work either.

I was thinking in the using of PTC 1000 (because I already have it, that´s why) or any PTC, NTC or pt 50 or pt100

I only need the circuit, no pcb. If you know a place on the internet where I can find something like that I would really appreciate it very much. As I said before, something simple no big thing, but I need it with a 2 (or 3 not important 3) digital readout so my wife can see the temperature in the oven. Thank you again for your help and time, thank you.

Reply of EU

Blind Dial Proportional Temperature Controller

Blind Dial Proportional Temperature Controller

See this blind proportional temperature controller, pdf here Analog Circuits and use the display temperature controller, display, pdf here Temperature Control Circuits on same page some digital indicators are there use them for display.

You could also try this High Reliability Thermostat, i found it very interesting, pretty simple.


Thank you AGAIN!! Thank you for your help and time. It´s just what I need!!! Thanks a lot!!

reply of EU

Sunday, January 18, 2015

Mystery of the Switching Paradigm

I was not able to solve a issue with an Enthusiast who tried building a Power Circuit Design of mine. It was a design that was not complete in documentation. I had just put it online for people to study. Marin built it and went thru a lot of trouble.- This was in 2005-6

Story Starts Here -

I built switching power supply with SG3524 (project del20020) from your site

It is working, but not good :-( Voltage and current regulations are very bad. I connect  stabilized 13V to input, and from another stabilized power supply I connect 12V for SG3524 and LF358. For testing I use mosfet BUZ11, and various ferrite inductors, but results are bad.

On output I cant get more than 6V, and output 470uF elco sounds like "bzzzzzzzzzzzzzzz"   I checked, and rechecked all connections several times, but everything is like on your schematic diagram.   Could you tell me if your schematic diagram has any bug?

Did you built any working switcher with this schematic?   Maybe is problem in inductor. Is it critical? I tryed with few toroid and ETD44 EI core with 4 to 40 turns of wire, with no luck :-( Which corre and numbers of turns do you suggest?

Power Supplies Section

Mail from Ing. Marin Antic

Mystery of the Switching Paradigm

delabs Reply

This i  a 15 year old circuit and working well, there may have documentation errors. i will look at it when i have some time. meanwhile troubleshooting is better.

The circuit itself can have errors, and then while you breadboraded there could be mistakes. the inductor is required for proper working around 50uH you will need a LCR meter or make a test jig.

Where is the bzzzz sound coming from is it a lose core of inductor vibrating. you said voltage is 6V does it give good curent, is load regulation good.   the input power needs to be 3-4 volts more than what you need a t output try 15V and also does input power suppy have good current rating like 5 is the input power supply able to able to drive the load you want. probably the input power supply may be loaded.   see for any heating parts. the problem is in the connections or the feedback path. look around the LM358, you can chat with me online. i will certainly try my best to help you.

I think that your schematic can't work good. Do you have continuous voltage and current regulation from 0-12V and 0-5A on your swicher? I think it is impossible with this schematic...

When I modificate sg3524 output stage to the mosfet, I got full voltage on the output not only half like before. But voltage regulation is not continious. Now I can regulate voltage only 6-12V. 0-6V not working. On 6V is step, and then continious regulation.

 I tryed many modifications on connecting LF358 to the output, an now is working. Not very good, but good :-)   Current control is not working ok. What do you think to move current sensing on positive output, not on negative?

mail from IMA

delabs Reply

Just check these points.

vary inductor air gap, make it also more like 100uH. Keep current limit to minimum and try. Or to locate problem disconnect pins  4-5 and then connect 4-5 to ground. Now current control has been disabled, see if vtg control and load-line regulation ok.   C2 and R10 fix frequency of SMPS 2.2k and 10nF plastic, verify.   Mosfet drive part may have to be modified bit as per circuit attached.   try all in the order show or as your understanding..

(see a application note below, not the circuit being discussed but the chip)

sg3524 smps

Friday, January 02, 2015

HV and Jacobs Ladder or Climbing Arc

I mess with HV stuff and recently I went to adjust my Jacobs ladder with it still switch on I griped  each leg of the ladder with my hands . I had a zap  5Kv at 100mA up my arms and across my chest   Why it did not Kill me is beyond my understanding as it is 3 times the accepted lethal power I have made several changes to the set up now including a physical barrier to the wire legs to prevent a re-occurrence

I will not let my 4 year old Grand son play with the above wooden toy pole pig and helical Jacobs ladder either - I promise

JAH from USA

James Howells Spark

James Howells Spark

i would be glad if you move away from high-voltage to high-current or online education, your experience may be useful to many.  as far as your survival from the zap, it is the grace of god indeed. do not press your luck too far, even god is very stressed right now.

The zap takes the shortest path, left hand to right leg, right hand to left leg 100mA can be fatal. If you were wet or sweating, then the surface of the body provides a safer path. Use silicone gloves and good shoes.  Only a Knight in Shining Armour is safe, not for his chivalry but for his conductive coating.


Additional Information about Safety with Electricity

Never use Smartphone or Tablet while charging (Near Sensitive Ear or Face). You may get electric shock or lightning discharge leaks. Use Surge protected Switchboards and Isolation Transformers or CVT. The mild shock due to Y caps of EMI filters is not a danger.  If the mains adapter you buy is low quality or there is a freak breakdown, you had it.

The risk is greater when a high voltage leak happens near the ear or face. and Metal parts of the phone gets close to the ear or neck is unsafe. The head and neck have very low resistance and can be damaged with much less Fatal Current.

Use total plastic exterior phones/tablets, wear shoes and use the speakerphone option when you talk/use while charging.