Hi I have relay module, I do a reverse engineering and draw a schematic of it, please find it in attachment. When I turn on the relay by DO, measured AI on some other pin rise about 300mV, how-to filter this distortion ? If I put a capitator 0.1uF between VCC and GND on relay modules it will help ?
I have similar problem with DC motors
and 0.1uF helps 
This is a photo of my board, relay is connected to the “Heat Realy” and distortion is on Analog input on “PH” pins. The schema of circuit I post in previous post is a schema of relay module not my board, relay module looks like this:
Transistor on relay board is 2TY
Cannot tell that much from your circuit board, no idea what the components are, you really need to post a full circuit diagram.
Think you are saying you are seeing a voltage rise on Analogue pin A1, have you measured the +5v rail ?
No details of your PH amp circuit ?
When you have a heavy load like a relay on the same voltage supply as the micro, then when the relay switches you will exeperience a voltage drop /surge, but that depends on how regulated your power supply is ?
We have no details of that, its voltage, current available and regulation / capactiors ?
Several ways to overcome your problem, better power supply and capacitors, consider using a 12v relay so you remove that load from the 5v rail.
We need more detail from you ...
We can skip all elements values on my board because i test this behaviour even all of them are disconnected, i post my board only for better view what I am doing, we should focus on relay pins and PH pins, only this are connected.
Ph metter is this one:
Like I mention I have a similar problem when running DC motors, I describe it in another topic,
When I connect a 1uF capitator between + and – of dc motor problem was solved, so mayby I should connect the same capitator between + and – of a relay coil ? Do You think it have sense and it worth testing ?
Yes, have seen your other post - and the common factor is your PSU.
Without details of that its hard to suggest anything as that is the first factor in the whole circuit.
My PSU is a laboratory DC power supply, set to 12VDC.
What do You think about putting 1uF capitator between “-“ and “+”coil terminals on relay module ?
porlock:
My PSU is a laboratory DC power supply, set to 12VDC.What do You think about putting 1uF capitator between “-“ and “+”coil terminals on relay module ?
OK, that should be an ideal supply, so do you have any current setting on the PSU ?
If thats your 12V supply, how are you creating your 5v regulated supply ?
What electrolytic capactitors do you have on the 12v and 5 v rails ?
If those power rails are ok, then try 100uf or greater across VCC and 0V on the relay board; NOT across the relay coil.
You can get by with adding caps here and there, but getting the basics correct is a better way.
Trouble is so many folk design and have a pcb printed , only to find their circuit does not work as expected and then try and find solutions that fit the pcb they have.
The right way is to build a prototype on breadboard or better still soldered stripboard etc, once proven then make the pcb.
Even seen folk complain to the pcb manufacturer that the pcb was faulty, but I was eventually able to show them it was their own fault because of an unterminated track in their design.
