So I'm using this 8 Channel Relay board and I'm trying to power it with a single power supply. When I remove the jumper, hook up the external power supply, and check the VCC pin that is supposed to go to the Arduino and power it, I measure 0V. I have the wired up just like the diagram I found on this forum. Any insight?
Let's see a good image of the PCB you have, and schematic if you can find one.
Let's see a good image of your wiring.
Check your reference points. It appears they are not the same. That is another way of saying connect your grounds.
gilshultz:
Check your reference points. It appears they are not the same. That is another way of saying connect your grounds.
If the OP is using that circuit correctly, you do not connect the grounds.
steigede:
When I remove the jumper, hook up the external power supply, and check the VCC pin that is supposed to go to the Arduino and power it, I measure 0V. I have the wired up just like the diagram I found on this forum. Any insight?
Sorry, but this diagram details only the connections between the relay board and its power supply, and the Arduino.
What we need to know to make sense of your confused description is what you mean by "power it with a single power supply", what you are in fact using to power the relay board and the Arduino, what "Arduino" it is, what all the connections are and where you measured?
A photo of your complete setup would be most helpful however unless you are a professional photographer, are equipped and know what you are doing, do not attempt to take photos inside.
Take your parts outside in full daylight but not direct sun. Use a real camera able to focus in detail and if it has no "macro" function, keep at least half a metre away and use the (genuine) zoom.
Here's the schematic. The device I'm manipulating needs relays to provide VCC signals and GND signals to operate. It works fine when the power supply is not connected to the relay board, the relay board jumper is in place, and the arduino is powered via USB.
When I remove the jumper, attach the power to the relay board, I see no voltage on the relay board's VCC pin that is supposed to power the board.
Edit: I inserted an image but it doesn't look like it's showing up. URL here: Imgur: The magic of the Internet
holdingpattern:
This (version of that) diagram is also floating around the forum, and is better since it explicitly shows the Arduino needs its own power:
Yes, that diagram represents how I have it wired up and working. I guess the diagram I found and posted made it look like the arduino could be powered by the same power supply I was using for the device I was controlling. I'll just power the arduino with the USB cable then. Thank you!
OPs image
Edit: hmmm... something about grounds... I have to admit that I do not see how this can work without a ground from the arduino to the relay board.
The only connection needed from the Arduino is 5V to an opto coupler anode and a connection from the opto's cathode to an output pin that when pulled to GND, illuminates the opto's LED and causing the output transistor to conduct, energizing the relay coil.
holdingpattern:
And according to your imgur pic, you're whacking 12V into a 5V relay.The Songle data sheet says the maximum voltage is 110% or 120% of the rated voltage, depending which ones you have. So that's 5V5 or 6V tops, not 12V.
Did the smoke get out, I wonder?
No, that's just the control voltage. The output on the relays says 250VAC or 30VDC.
vinceherman:
Edit: hmmm... something about grounds... I have to admit that I do not see how this can work without a ground from the Arduino to the relay board.
Because there is the 5 V "Vcc" from the Arduino to the relay board, which is the necessary return. The return is only ground if you are driving things HIGH.
So, is it a 5 V relay board (the voltage is printed on the relays) or is it a 12 V relay board? You need to power the relay board - by GND and "JD-VCC" by the correct voltage. The control inputs will in either case operate from the Arduino just fine with "Vcc" connected to the "5V". pin.
I have done exactly the schematic of post #11 (Arduino and 8 channel relay 5V).
It works perfect for about two hours, and after that Arduino freezes.
If I disconnect the relay from Arduino (IN and 5 V), Arduino never freezes (so, I don’t think that is something wrong with the code).
If I implement the post #4 schematic, I see the corresponding leds to be on, however the solenoids are not activated.
I use 5V 4A power supply connected to JD-Vcc (5V) and Ground next to In1. I use also another power supply 5V 800mA for the Arduino.
I see (with multimeter) that the ground near to Vcc JD-Vcc and the ground near to In1 are isolated. Is that normal?
I ‘m going to replace the relay, but before this I would like to have your opinions.
Thanks in advance!
What are the relays switching?
1 for a heater (220V 60W), 2 for a water valve (220V less than 10W) and 2 for fans (12V less than 12W).
stelios232:
1 for a heater (220V 60W), 2 for a water valve (220V less than 10W) and 2 for fans (12V less than 12W).
Have you kept the 220V wiring away from the rest of your circuitry.
What is the application?
Can you draw by hand a complete circuit diagram including labels on components.
Can you post a picture of your project please?
Thanks.. Tom... 
I made a stupid mistake and I had condensation on some contacts...
Now its ok.
Tom, thanks for your interesting!
