Tuesday, May 28, 2019

CJC or Cold Juction Compensation

About a month agoo I asked a few explanation on blind controller circuit design, up now i did focused on mechanical parts of my rubber press and now these are ready, i turned myself to the controller :

Qestions came up as I tried to duplicate part of your circuit design on a bread board and could not get a significant reading on DMM.

Why value of TH1 is 5 ohm in this circuit ...in other circuits you design it is mostly 12 ohm ?

I used document DACT0006.PDF to make TH1 and re-calculate values of resistors involved around OP07 for gain and R26 using formula you gives. R26 : 330K ? to not induce anyone error i won't replicate here these calcul, but could you confirm me this value ? (sorry for this one I know it is unpleasant : think I'm lost... )

Mail From SY

Another Method using a Copper Resistor

If wires of two dissimilar metals are joined at both the ends and the junction formed at one of the ends, is heated more than the other junction, a current flows in the circuit due to Seebeck thermal emf. This effect is used in thermocouple temperature sensors.

Thermocouple Temperature DPM - DMM

Thermocouple Temperature DPM - DMM

The Peltier effect is the converse of above Seebeck effect, which means that if a current is forced through junctions of dissimilar metals, the junction will generate heat or absorb heat (cooling) depending on direction of the applied emf. This effect is used to make portable and small refrigerators.


What is the range i should use for DMM for this blind proportional circuit ? what should be the reading ?

Iideal for my purpose will be 1mV per degre Celcius as cheap panel meters range 0- 200mV

One of LM324 operational amplifier output is connected to ground... which is separate from VDD, could you explain me more?

I 'm making now the box that will contain the circuit and support the press itself. When I get over this stage i will make pictures, is 100Kb suitable size to send you ?

Mail From SY

Radar using Laser - Detectors

Radar using laser and microcontroller will u pls help me and provide me the necessary info.

Mail from  VV

Here are some pages in the web that may be useful in your study ...

Integrated electronic and optoelectronic circuits and devices -  for pulsed time-of-flight laser rangefinding

The main focus of this work concerned with the development of integrated electronic and optoelectronic circuits and devices for pulsed time-of-flight laser rangefinding is on the construction of the receiver channel, system level integration aimed at realisation of the laser radar module and in integration of all the receiver functions of laser radar on one chip.

Unusual Radar Detector

This unique anchient design uses a chopper amplifier - The microwave diodes are chopper-gated by a multivibrator so the RF signal level can be detected by an audio frequency amplifier.

 Laser Radar for Vehicle Speed

Laser Radar for Vehicle Speed

Abstract In this research work, new exploration of a pulse laser radar system is presented with two splitted parallel laser beams for the measurement of precise velocity of moving vehicles along with their contours and ranging distances. The emission of optical pulses is eye-safe, and hence the radar can be classified as a class-1 laser system.

Thursday, May 23, 2019

2.5 GHz Frequency counter

"Imagine you have a radio receiver and you wish to display the receiving frequency. As you know the oscillator in a radio receiver works 455 kHz or 10.7 MHz above the receiving frequency. The 455 kHz and 10.7 MHz difference is called IF (Intermediate Frequency)."

2.5 GHz Frequency counter

A Google talk around 2006 with another electronic enthusiast

davidhvm (3:36:51 PM): Hello, i assembled de prototype and work fine
davidhvm (3:37:24 PM): anyway i add a push button to Set/Reset to 00 the counter
davidhvm (3:37:39 PM): thanks a lot again
davidhvm (3:38:13 PM): check this 2.5 GHz Frequency counter
davidhvm (3:39:07 PM): i'm looking for some apps for counters and i
found a lot o pages with very usefull
davidhvm (3:39:44 PM): circuits of course with PICs (Microchip or Atmel)
davidhvm (3:39:47 PM): Bye
delabs (3:44:58 PM): hello david
davidhvm (3:45:37 PM): hi all work fine
delabs (3:45:48 PM): great
davidhvm (3:46:40 PM): are amazing these projects
davidhvm (3:47:15 PM): ok thanks may be for long time
delabs (3:47:30 PM): fine
davidhvm (3:47:41 PM): i'm at middle of my carrer

Monday, April 29, 2019

Battery Brightness and a Blinking LED

Many many thanks for this quick reply again.

We are also experimenting with stobing the LEDs very fast using digital out of the MCU's I/O to kind of PWM the LED to calibrate it properly for our application .

I plan to use 3 x AA batteries. If I add a 4th battery, The solution has to be really cheap since there will probably be 4 constant current circuits -

The 74HC14 is cost effective, so it's a possible solution if the circuit works well. Yes - I need to be 100% sure that the LED brightness is the same for full battery to say 80% battery

Mail from AB

You could look at this TPS61043: Constant Current LED Driver

The TPS61043 is a high-frequency boost converter with constant current output that drives white LEDs or similar. The LED current is set with the external sense resistor (RS) and is directly regulated by the feedback pin (FB) that regulates the voltage across the sense resistor RS to 252 mV (typical).

The 74HC14 can be used to drive-light 4-6 LEDs. It can be directly connected to MCU.

The LEDs should be flashed at around 5 Khz. Then a constant current source is not required.

Why do you wish to use constant current. Is it for a steady light.

If the problem is dropping voltage. Another battery or voltage doubler is required

An voltage doubler may not be cost effective. Another battery may be a simpler solution.

By using a 74HC14 you can avoid the PNP transistors. This is an inverter, you can use a buffer chip too.

A series resistor with LED or 10Kz flash is to limit current.

The 74HC14 just replaces your PNP transistor saving 1/2 a Volt. The Microcontroller PWM can be used to control brightness. Then you can skip even the series resistor. You can even use a 555 chip for pwm.

Flashing must be above 1 KHz. The persistence of Vision is 20mS. Very high rate will make it dim, something optimum.

A better Idea is to use LM317 to get 3.3V regulated supply from 5-6V of batteries. Use this regulated supply to drive LEDs. This also needs to be tried practically. As voltage is constant the current in leds will be constant. for 20% drop.


Sunday, April 28, 2019

The Return of Bright LED

From my Thunderbird archives. it may be interesting to read, maybe you may learn a thing or two.

Many thanks for your quick reply - much appreciated. The FET solution is new to me, but I have tried most of the others.

I think the problems are:

1) As voltage for these LEDs drops from 4.65v, fairly quickly, the constant current starts to move.

2) The 'constant' I can acheive would be only 4% while the current is stable.

Do you think my problem can be solved? Many thanks again,

Mail from AB 2006

NSSBC : the status indicator

On the right we see the status indicator drivers. One 74HC14 gate buffers (and inverts) the signal. The other gate re-inverts the signal. The trick now, is to mount the LED and resistor in parallel to the second buffer gate.

The Return of Bright LED

The example above may be the solution you need...

The LED you use needs 20mA at say 3.3V as per datasheet you sent. 3 AA batteries are 4.5V right, and say 20% drop is 3.8V ok.

Of the 3.8V 3.3 is needed by LED we have only 3.8-3.3=0.5 left With 0.5V dropped across Control Transistor PNP, you have nothing left.

A simple idea is to use a cmos chip 74HC14 to drive LED. Instead of constant current you flash LED at High speed. This way Battery and LED will last longer and work at lower voltage.

1.5 Volt LED Flashers

The LED flasher circuits below operate on a single 1.5 volt battery. The circuit on the upper right uses the popular LM3909 LED flasher IC and requires only a timing capacitor and LED.

1.5 volt dual LED flasher

This 1.5 volt led fasher runs more than a year on a single 'd" cell and alternately flashes 2 LEDs at about a 1 second rate. The circuit employs a 74HC14 CMOS hex inverter that will operate at very low voltages (less than 1 volt).

delabs - 2006

Saturday, April 27, 2019

Driving a LED from MCU

I just read your blog and found it very helpful - thank you.

I am working on a new toy project and have a problem I think you can help with.

I am turning an LED (see attached) on and off from a small taiwanese MCU (like a PIC chip). I am using a PNP transistor for this.

My application needs constant current to the LED from 3xAA batteries down to about 3.6v-3.8v. Since it's a toy, the circuit has to be very very cheap! So far I have only managed 'constant' to be about a 4% drop, but I need to do better.

I need a circuit which includes the PNP from the I/O pin of th MCU. Help!

Mail from AB USA in 2006

I am trying to understand your need. All you need is a PNP transistor driving a LED. A series FET constant current element has to be added.

Current Source for LED

The circuits below can show parts of the circuits. If you need something special, i can design for you.

 Constant Current Source LED Drive

A current source based on a JFET

In Lecture 1 we introduced the idea of a current source, and mentioned that these were slightly more difficult to implement than the perhaps more familiar voltage source.

White LED Stroboscope

With Constant Duty Cycle and, Constant Current Drive. The circuit is composed of an oscillator, a pulse slicer, and a gated constant current source. All of the circuits except the anode of the LED receives power from an LM78L05 5 volt regulator.

delabs - 2006

Wednesday, February 27, 2019

24V and 25V Power Supply with 2A Current

I am looking for a 25V Power Supply with 2A current for my Application. A regulated supply.


Here is a simple to build regulated power supply. The two diodes are to boost the 24V to 25V DC. It uses regulator 7824 and TIP2955 PNP Transistor to boost current.

24V and 25V Power Supply with 2A Current


Thanks alot! Do you know of a good transformer manufacturer that has the one you specify? Also, is that "100V 3A" at the bridge the rating on the diodes? Also does the transistor circuit increase the voltage to the regulator so that it is 3 or more volts above the regulating voltage? Lastly, is your ground reference on the gnd of the regulator?

Wait, one more....this is + or - 25 volts correct?
Thanks alot!


1. choose a transformer with a close match of what is available.

2."100V 3A" at the bridge is the minimum diode rating also(or use 4 x 1N5408). "100V 3A" is also minimum bridge rating use a close match.

3.to make a bridge with 4 diodes refer my other circuits, there are many.

4. 22V AC leads to around 30V unrectified DC which is good, if the 30V becomes more, the heatsink needs to be very big.

5. the ground of regulator is lifted by (0.7*2) by 2 diodes to provide 1 V above 24V, as 25V regulator does not exist. the power supply 'neg' can be grounded or earthed,

6. the supply is a+25 V from ground or negative, but things are only relative.

7.if you need a dual supply 3 terminal , that is ground +25 and -25 then for -25 one more circuit using 7924 and tip3055(npn) has to be made.

8. use any high current pnp transistor (5A) you have put a heatsink with heatsink compound.


Monday, February 25, 2019

UPS and Inverter Schematics

Do you perhaps have an inverter schematic for a sinewave inverter or stepped squarewave using the SG3525 chip.

I'm also interested in connecting the inverter to the grid via a solar panel. I hope to reduce my electricty bill by pumping power into my 220v system. Do you perhaps have circuits to synchronise the inverter to the 50hz main.


Nice to get your email. .. Have you seen the circuits in my page....

Power and Energy Schematics

Switch fast from mains to inverter. The inverter is always on with the battery charged by the mains.

UPS and Inverter Schematics

The mains load is of two types

lighting low current 5A ??  and  heating high current 20A??

You should isolate both of them, the UPS is only for lighting. For heating you need a very big UPS, solar will not help, oil might.


I want to build a home UPS System. Uninterrupted power supply for computers and with Solar Cell Integration. I need some Schematics..


You have to design and develop these equipment, just a circuit or instructions will help you learn but you cannot make a robust product. Anyway have a look at these applications to learn ..

Sine wave Inverter 800VA

Learn about UPS here  UPS Power Inverter and DC to AC


Hobby DIY Electronics