I have noticed some relay boards have a jumper for VCC-JDVCC along with an additional ground pin next to it(additional to the ground that is inline with the arduino VCC as well as the data pins)
Other boards seem to just have the VCC-JDVCC with no additional ground
I am powering a 120v AC item, and want to be sure and isolate from the arduino.
Im found this picture in an older message, but have a concern.
First, does this diagram seem correct?
Second, if it is, without a ground to the arduino, how would the data pins be able to complete their circuit in order to complete a circuit and carry out a digitalWrite High/Low.
You must tie the arduino ground to your 5v. power supply ground. As to isolation of the mains power from the Arduino, the mains power will only be carried through the relay contacts. It doesn't appear to have any routing on the board itself. Looks perfectly kosher to me.
mauiman808:
First, does this diagram seem correct?
Second, if it is, without a ground to the arduino, how would the data pins be able to complete their circuit in order to complete a circuit and carry out a digitalWrite High/Low.
I have used that wiring schema, and it has worked.
As I understand it (and I stand to be corrected), one side of the led in the opto isolator is at 5V. The other side of the led in the opto isolator is connected to the Arduino pin. When the Arduino pin is pulled low to around 0V, the circuit is made, and the led in the opto isolator emits.
Steve
the JD-VCC to VCC jumper allows you to power the relay with the same supply as the Arduino VCC. You can isolate the two by using a different power supply for each Arduino VCC and the relay JD-VCC. If you do that, you end up with three power domains
Arduino VCC -- broken out on the 6 pin header in the diagram
relay JD-VCC -- broken out on the JD-VCC pin (shares ground with Arduino VCC)
mains -- always isolated from the two above
mauiman808:
First, does this diagram seem correct?
Totally and absolutely correct.
mauiman808:
Second, if it is, without a ground to the Arduino, how would the data pins be able to complete their circuit in order to complete a circuit and carry out a digitalWrite High/Low.
because they pull LOW to actuate the respective relays. The circuit is completed through "Vcc" to the Arduino.
Tell you what, here is the actual circuit! Check it out:
Note the controlling circuit to the optoisolator on the left hand side uses "IN0" (or of course, "In1") and "VCC" only, while the isolated relay supply on the right uses "JD-VCC" and ground. The jumper is removed.
