Sunday, March 19, 2017

Coffee maker PID Temperature Control

My name is RP  i'm working on a project to regulated the temperature of a coffee maker. I don''t know were to start. what i want is to regulate the temperature of the coffee. Could you please help me.

Mail from RP


This is what you may have to do. study below pages and try.

Murph's Silvia PID Page - This page describes my effort to improve temperature control in a home espresso machine by installing a PID temperature controller. If you are reading this page, then you probably already know what Silvia is, what PID means and why anyone would want to add one to the other.

Coffee maker PID Temperature Control

Tuning a PID (Three-Mode) Controller - . If the controller does not include an autotune algorithm or the autotune algorithm does not provide adequate control for the particular application, the unit must then be tuned using a trial and error method.

PID controller - Wikipedia - A PID controller continuously calculates an error value {\displaystyle e(t)} e(t) as the difference between a desired setpoint and a measured process variable and applies a correction based on proportional, integral, and derivative terms.

Temperature Control - PID and LabVIEW - First, let's take a look at how the PID controller works in a closed-loop system using the schematic shown above. The variable (e) represents the tracking error, the difference between the desired input value (R) and the actual output (T). This error signal (e) is sent to the PID controller.

delabs

Saturday, March 18, 2017

Halogen bulb lamp dimmer circuit

Can someone provide me a (simple) schematic for a dimmer that would control 12 VAC about 80 watts. This would be used to control a lamp with halogen bulbs.

A comment in Hobby Hound

Here is a listing study them and choose, try out, learn and then build the one right for you.

1200 Watt Lamp Dimmer Circuit The following circuit is a lamp dimmer circuit that is capable of controlling up to 1200 Watts. The circuit uses the Q4015LT combination Diac and Triac that is available from Digikey Electronics.

PWM Motor Speed Controller / DC Light Dimmer - Here is a listing study them and choose, try out, learn and then build the one right for you.

DC Controlled Dimmer Velleman kit - K8064

Halogen bulb lamp dimmer circuit

Simple brightness adjustment by means of a DC voltage, optically isolated adjustment input. Pre-set adjustment for full brightness, suitable for incandescent lamps, mains voltage halogen lighting and low voltage halogen lighting in combination with a conventional transformer. "Soft start" feature to ensure lamp longevity, transformer protection in case of defective light sources

Electronic Transformer for 12V Halogen Lamp - STMicro
The topology of the circuit is the classic half-bridge. The control circuit could be realised using an IC (so fixing the operating frequency), but there is a more economical solution which consists of a selfoscillating circuit where the two transistors are driven in opposing phase by feedback from the output circuit.

delabs

Friday, March 17, 2017

How to Connect RTD to transmitter

Can you explain me were i have to conect the three cables of the PT100 in the Circuit RTD-Pt-100-Transmitter Circuit?

RTD PT100 Transmitter and Multiplexer

Comment from CV of Spain

You have a three wire RTD, there is also a 4 wire RTD type, This circuit can be used for both.

In the 3W RTD you have two wires coming from the same point (zero ohms between them) the third wire will be 100 ohms from these two. From the two wires that are at same point take one wire and give 1mA from Q3 + OUT. The other wire of the pair connect to input +..... input - can be connected to the 100E end.

How to Connect RTD to transmitter
delabs

So imagine that I have three wires one white and two blacks.

One black to +OUT 1ma
Other black to input-

And waht about the withe one that is the one that give me arround 100ohms??

Reply from CV

Black 1 - +Out 1mA
Black 2 - +Input
--------------
White goes to -Input

See NI Developer Zone - RTD Connections

delabs

Saturday, February 11, 2017

Battery Management and Supply Design

As you have have pointed out, my circuit is not driving any motor or such loads...but it is driving a Wireless Module which draws about 165mA to 240mA from my circuit during transmission [for 4 sec] and normally it takes upto 114mA. After a time-out of 1min, I put my uC P89V51RD2 to powerdown mode [200uA in this state].

Read articles in the link you provided, thanks for that! - Continued from uC Board is Misbehaving on Brown Out.

My other problem is that my batteries get supercharged upto 5.8V, and as per spec's of most IC' they are bound to operate faithfully upto 5.25[max 5.5v], so how do I solve this issue? I want that my boards get only 5.25v even if my battery is having voltages 5.25+, without increasing my existing current consumption to noticeable value.

Moreover I'm in need of a cutt-off circuit which will take away the load from my batteries when my battery has reached 4.00V, & the charger charges my battery independently. Do you have any thing which will suite my purpose?

Mail from MO

Have two supplies, the one for uC can be a small Ni-Cad battery charged by a diode by the bigger battery which supplies the 200mA for RF drivers.

So when the big battery is loaded and the supply dips the shock is not felt by uC. or isolate it by SMPS and isolate the grounds. The ground return current of RF module 200mA must be lifting the ground of uC or some Logic.

Start by trying to locate the problem, first power RF and uC boards with isolated lines from two lab-test 10A power supplies. If both are in same board, cut tracks and power them separately. The grounds should meet at point the two sections interface.

If that works without problem, you know it is related to supply, now step-by-step go back to the battery and charger you have built keeping isolation intact. Look for spikes-glitches on power lines of uF when RF module active. Check if that is close to or leaking RF to uC circuits.

The battery charger circuit should limit voltage and current to battery specs. If you are not using a charger chip then while testing make sure the charger has a regulator or use LM317 to clamp voltage to 5.6 or 5.5 as per your design.

There are charger chips from maxim, national for battery charge management. If you have a need for extra voltage the you have to use SMPS boost switcher. which may take the low battery 4 to 8 which can be regulated to 5 using 7805.

This may be getting bit complex, first try to find what is the problem, it may be just the board design.

Battery Management and Supply Design

You can also use a Single Maxim Chip for all these functions. ...

Supervisor ICs Monitor Battery-Powered Equipment

A feature-laden µP supervisor (IC1), with the help of the µP itself, performs a variety of functions in this typical application circuit. You can get these functions all together or in various combinations, by selecting one of the many available microprocessor (µP) supervisor IC....

delabs


Wednesday, February 08, 2017

RS Latch Erroneously setting by Itself

I am having trouble preventing my rs latch from erroneously setting. The circuit is a voltage threshold detection circuit with a nand gate whose output is tied to a SR latch.

I have capacitors across the VDC and ground for the chips and I verified the power supply's input is fairly stable. As further troubleshooting I probed with a oscilloscope at the SR latch's input and looked for anything above 1 V. The voltage never moved above 1V, but the latch still set.

I was able to place a .3 uF capacitor from the SR latch's input to ground and this seemed to fix the problem. However, it does not explain what is causing the latch to set. Any ideas or suggestions would be much appreciated. Thanks.

Some info:
Nand gate: SN74LS30
SR Latch: CD4043B
Supply to ic's is 5V from a LM7805 (with .1uF cap's across input/output)
Voltage threshold detection coming from LM339 comparator

Basic idea:
Vin ----------> |LM339 pin 4| -> |nand gate| -> |SR latch| -> |(relay driver circuit)|
Vthreshold -> |LM339 pin 5|

Mail from SM

If the power supply is stable and you do not have ground loops then that is not the problem.

If a relay or LED or some output is being driven, the current pulse may be triggering the circuit. Isolate Grounds of Loads even LEDs and Relays, Ensure EMI-RFI immunity.

RS Latch Erroneously setting by Itself

Flip-flop (electronics)

Use a 400MHz Scope and set timebase to uS-nS and see if a Spike is causing the trigger. Set the brightness level a bit high and look as close as you can.

Even a IC consuming a little extra power for a mS can set up a spike in the rail. Keep power and signal circuits on different PCBs when designing.

Check the environment and mains wiring, It could be a Laser Printer sharing the mains. If a Loose contact is present in mains box then your test circuit links with printer. Finally a good earth or ground is a must, if the unit is to operate on mains.

In the LM339 comparator use a Hysteresis Resistor feedback of 10M or 1M, Also a small cap can be placed across 10M, like 10nF if the system is a slow response one. Ensure you do not put a cap in a way to cause oscillations. A RC at input of LM339 may help.

Finally a LM339 output may have to go thru a schmitt nand buffer like 4093. to Clean the signal. Interface from a LM339 may be good with CMOS and not TTL, so a Scmitt can be tried. Nand gate: SN74LS30 and SR Latch: CD4043B seem to be different families. Use the 74HCT30 and 74HCT4043, use any one single family in Logic.

delabs

One thing i left out, The power on Start of the circuits must be defined. So a power on Set or Reset Cap with a pullup has to be provided if it is triggered by a Low. If you use a Latch which triggers by a Positive Edge then A pull down R and a Pull up Cap is required. - delabs

Sunday, February 05, 2017

Isolated RS232 interface to Microcontroller

I've seen on the net the schematics for RS232 with Opto-Isolation. The supply on the PC side is from the PC. The supply from the line side is external? I've seen the 3 connectors (RX, TX & GND) together with 2 connectors 5V. One of them is connected to the device. How about the other? Needs additional power source?

Could you send me the PCB and component layout, as well as the component list, I'm afraid to get mistaken

mail from CS

The the circuit you are referring to is... RS232 with Opto-Isolation
The Blue line indicates the Optical Isolation, no wires or cooper should cross this line. Yes the PC Powers the left side, The supply to the right side is the Microcontroller supply. The Microcontroller will have a +5 and GND use this for the right side of opto. I have no PCB for this. You can make your own PCB using eagle cad. I made this circuit as i could not risk my PC and had no other components. I had to make a high voltage measurement with the PC, so this caution.
Also use the Max232 if you do no need 1KV Optical Isolation.

Here is a interface from RE Smith Inc, the one below is not isolated. They have Isolated versions too.



The RS422S is a fast Async bi-directional RS232 to RS422 interface converter that will operate at data rates up to 115.2Kbps. The unit has jumpers termination, RS232 DTE/DCE selection and, TTL/CMOS operation. The unit has two RJ11/12 connectors an a pin header for power, common TTL/CMOS TX data and RX data.

Discover Circuits - Opto-Isolator Coupler Circuits
RS232 to RS232 Port Powered Optical Isolator: Brochure with schematic in PDF format / (added 7/02). RS232C Circuit has Galvanic Isolation:

delabs

Wednesday, January 18, 2017

Room Temperature Monitor and Alarm

I am required to design an electronic system that monitors the temperature between(22-24 degrees Celsius). Given are power supply, Analogue subsystems and digital subsystems. the accuracy of the digital control circuit is limited by the accuracy of the temperature sensors. A green LED is lit to indicate correct temp range.

Room Temperature Monitor and Alarm

A red LED indicates out of range temperature and in sustained events( where this indicates out of range temp which is counted, displayed and timed) a large LED is lit. In a event where the sustained event exceeds 6 days an alarm is sounded to indicate a possibility of a system failure.

Now I need help on how to come up with the correct circuit diagrams which can work , how to simulate and to get the project done, please help, even direct me to books on the project or other sites please...

Mail from AM South Africa

First acquire the room temperature as an analog value. This requires a sensor for the range you indicated a Semiconductor sensor like LM335 will do fine.

Use the ideas on this page - Circuit Design Service and Projects 

Now monitor and generate Logic outputs for temperatures out of range using a Window Comparator. Then for the timed events you need a Timer circuit. And a Logic to set off the Alarm or Annunciator.

All this can also be done by a PIC circuit if you can write some code. I have given some pages to see, study them, that will be sufficient
delabs