Photo resistor and relay problem.

Hi i got my arduino hooked up with an ethernet shield and an mqtt program running on it. The arduino sends data to my raspberry pi where i can monitor temp/humidity and light on node-red and i can even control a relay board with 4 relays. Everything works great till i activate a relay then the photo resistor value increase and if i activate another relay it increase again. suspect maybe a voltage drop or something. But i tought to ask if anyone have any better idea what the problem can be.

Do you have a multimeter to check the relay coil-voltage?

Have you tried a simple-little test program that just activates/sequences the relays?

Yea i got a multimeter at work. No i haven't tried the relays yet more then that they work on off all four of them. As im at home and dont have my multimeter here. like i wrote i suspect maybe a voltage drop that all i have to go on at the moment if im not missing something.

Probably caused by an insufficient power supply. What is your supply's current capacity?

Yea i got a multimeter at work

With the kind of project you're doing, you should probably get one for home. If cost is an issue, a cheap meter is better than no meter.

In the meantime, you can make a tester with an LED & resistor to check for the presence of voltage, and if the voltage drops with more than one relay energized, the LED will dim.

Many years ago, I made a low-voltage tester with a meter probe, an alligator clip, two different colored LEDs, and a resistor. The LEDs are wired in opposite directions so I can check for positive or negative voltage. ...Sometimes it's handier than a meter.

Check your grounding... Take a quick look at "Common Ground Point" on this (incomplete) Page

Welcome to the forum.

Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png?

Can you post a picture of your project so we can see your component layout.

What spec/type of relay are you using?

Thanks… Tom… :slight_smile:

Check your grounding… Take a quick look at “Common Ground Point” on this (incomplete) Page

Tnx. It was the grounding. The resistor and relay board shared the same grounding on the breadbord. When i gave the resistor a direct grounding to the arduinoboard everything worked.