Q3 is driving only the relay right? If so then i don't understand why you have used D33. And why you have used C8 for relay. The relay coil behaves like an inductor. Don't you think that there would be some kind of resonance which affects your signal. Try removing C8 and check.
The switches at left side RB0,RB1 and etc are poorly attached. never leave ports open so they will pick noises. Use pull up/pull down configuration.
Using oscilloscope check if there exist frequency near Al1 port (Use analog oscilloscope), if yes than try adding different values of capacitors and check if frequency is vanished. 0.01microF for higher frequency 0.1microF for mid and 4.7microF for low frequencies. These values are used typically.
Check near regulator if there is some noise frequency. When i connect ADC0808 with NE555 timer of frequency of 200Khz, a frequency also exists at my regulator LM317 which is vanished when i connect 22MicroF capacitor.
Also check noise at Al1 when relay is turned off/ON.
What is the use of R19-R26 resistors?
Why are you using 24Vdc use 12V or 9V power supply and remove Q1. because first its an extra circuit and i know you added it to keep potential difference low so your 7805 wont heat up. Depending on requirement most of the voltage may drop at R29. may be this can also be the reason of your problem.
This means you have to check all the possible solution, Keith is right if its always a 10 degree jump then there must be a logical error. Trouble shooting is headache.Actually this project was already made by someone and I'm tasked to fix everything.
No it won't do the job. It measure voltage or current over 100msec of time and it averages the voltage. I don't have oscilloscope yet (I m going to buy used Analog Oscilloscope ) but i have Uni-T UT70A digital multimeter which can measure frequency up to 10MHZ. Try buying one of those...they are the cheapest and best budget price.I don't have oscilloscope yet. Will a 3 decimal places voltmeter do this job? I've tried using the voltmeter and never seen any fluctuating milli voltage even 1.
I believe that you can replace the transformer, its not that hard.The design utilizes a fixed 24Vac which is the output of a transformer from the 220Vac socket. The 24Vac was converted to 24Vdc via rectifier diodes (sorry I haven't placed it on the schematic) and used the transistor circuit to limit it near 12vdc.
Is it always a 10 degree jump? If so I would suspect a software bug.
Keith
This means you have to check all the possible solution, Keith is right if its always a 10 degree jump then there must be a logical error. Trouble shooting is headache.
No it won't do the job. It measure voltage or current over 100msec of time and it averages the voltage. I don't have oscilloscope yet (I m going to buy used Analog Oscilloscope ) but i have Uni-T UT70A digital multimeter which can measure frequency up to 10MHZ. Try buying one of those...they are the cheapest and best budget price.
I believe that you can replace the transformer, its not that hard.
This project is actually designated for the fryers supplied on us. The fryers have their own 24vac transformer so I need to convert it to dc using a rectifier diode.
Or maybe you could use a MOSFET instead of BJT? I mean some kind of low power one suitable for driving with 5v directly from uC.
Sajjadkhan, I'm thankful you're still concerned about the progress of my problem. I forgot to say that I'm averaging up 5 temperatures since I don't like to see temperatures jumping. With these there should be no temperature jumps since they are averaged. If I removed my averaging software routine during the time that the circuit becomes unstable and the temperature jumps with large values, I guess the temperature jumps will be even higher like by 20 degrees.
I was working before voltage measurement using ADC and I experienced unstable result and fluctuating but all came goodby averaging by 10 and i got more stable results without any changes in my hardware..
Your circuit is very compact so there should not be any noise as you are not using any long wire.
ok here is what you can do in your existing circuit. Replace r29 by 2Kohms. after that replace thermistor by a 10K multi-turn variable resistor i.e. one upper one pin to 5v mid pin to adc and lower pin to ground....see if the error still exist. do this without averaging. You can do this just within an hour....Do it and let me know. We are going to catch the error from its root
Talking about Analog ground... if you find voltage across any two analog ground then its a poor wiring or poor PCB track. Try to coat it with solder.
Talking about digital ground, they have a limit to sink current and if you are injecting more current then there would be a voltage drop and its not good for the chip.
And yea post a picture of your hardware based circuit,front view and back side in good resolution.
The noise comes from the 24vdc relay when turned on and off.
how did you know that the relay cause the noise?
I have the same connection before a bunch of relay and a controller but there is no noise happen.. try connecting the supply of your relay just after the 5v output of your regulator and of course you need to use 5v relay or 6v will do..
Averaging may or may not work if all the wrong values are averaged then what? I do average just for ADC own internal error or if the signal is varying. If there is noise then try to remove the noise.
Yes even i think relay is not a problem. and yes just put a 22microF capacitor at 5V output to be sure.
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