Hi, I've seen this problem a few times but I can't find a definitive answer. I'm using a 4 relay module which is opto-coupled and has a fly-back diode on every relay already (I'll attach a circuit diagram), the problem is I have to power my relay board and the arduino 2560 with the same 5v supply so it's not really isolated anymore. There's a 12V boost converter in the circuit that the relay is switching and also a tip41C switching on the negative side, so when the "IN4" on the relay is written low the 4th relay "COM" contact switches over to NO, where the 12V is supplied to, and then I'm writing High to the base on the TIP41C (through a resistor) so it basically will switch both the positive and negative. When doing a dry run the circuit works as it should and measured with a multimeter I get 12V from the COM contact (on the 4th relay) to the collector on the TIP41C. Eventually I'll be using this to power a small 12V sensor but in the meantime I have connected another Arduino mega to the 12V and the switched GND just to test it, If connected before the circuit is turned on it works fine, but if I connect the second arduino to the 12v and switched GND after it is already switched over then the first arduino will switch off, (and the 12V from the relay) and then it reboots and works fine. I know it seems like a bit of a strange and useless circuit but I'm using it in a bigger project that I won't explain here but it needs to be this configuration. this circuit should work but I'm assuming when put under load there's a voltage spike. I've tried putting a flyback diode across literally everything, the only other idea I have is an RC snubber but I'm not exactly sure where to put it. sorry about the rough circuit diagram.
Any help is appreciated, Thanks.
Post a real schematic.
The spaghetti drawing isn´t realy helpful.
Also some good, clear photos of your setup - so we can see your actual wiring.
Poor connections are a very common cause of this kind of problem.
Solderless breadboards are notorious for poor connections.
Rather daisy-chain your supplies (as the sketch suggests you have) wire each one directly back to the power supply - this stops high currents in one connection from "upsetting" other connections.
This is known as a "star" connection
Hi, @link123100
Sorry, but I had to spread it into some sort of point form to make it more readable.
Can you please post a copy of your circuit, a picture of a hand drawn circuit in jpg, png?
Hand drawn and photographed is perfectly acceptable.
Please include ALL hardware, power supplies, component names and pin labels.
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