Can I use this Relay Board with the Pi ?

Because This board doesn't have Opto-Coupler..can i drive it from 3.3v...will It Cause any Issue for Pi enter image description here enter image description here

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    Most likely yes... (But wait before connecting it...) Could you either try to figure out the wiring of one channel - that is one of the transistors, two resistors, a diode and a relay - or at least take a picture of the bottom side of the board? Could you also give the colors of the rings of the resistors? It's hard to make them out on the picture. – Ghanima Sep 4 '14 at 16:00
  • @Ghanima Circuit looks like above – user40138 Sep 4 '14 at 17:02
  • Are you sure about the 2k2 resistor. That does not fit the colors I can see - but then again it's kinda hard to tell from the picture. – Ghanima Sep 4 '14 at 17:10
  • Not the Value but Schematic is Correct.. just a min i will check the value – user40138 Sep 4 '14 at 17:11
  • it's a 11k Ohms (Brown-Brown-Black-Red-Red) 2.20k ohms (Red-Red-Black-Brown-Brown).. – user40138 Sep 4 '14 at 17:23

I was actually looking at using a relay DPDT or H bridge similar to that but if anything, I realised you were possibly using a solenoid like I am, I went to a few electrical engineers and they recommened that I use a irf640 for a 5v 1a (low voltage application) and if I needed to apply more power with less power consumption use a irfz44 (for high power applications) in saying that (read the documentation for a irf640p) the advantage is that as long as you are using a digital output that supplies more than 4v 750ma (check documentation because I'm going off the top of my head) the connection internally will complete the circuit and allow the solenoid to run.

But I must stress that dont use the 5v supply off the board because the spiking current pull of the solenoid might have a high chance of destroying your board, may I suggest also using an external power plug pack with an inline fuse (roughly rated at 1A-1.5A)

Otherwise make sure you use a 100ohm to 220 ohm in series with the base of the component because all it needs is a current limiter to protect the irf640.

Sorry I just realised you were using a SPDT on the output circuit, either way this all still applies as this can work for most circuits.

Hope that helped mate.


From the picture of the board, the schematics and the components values given it seems highly likely that the board could be operated safely from a RPi GPIO pin.

A flyback diode is included to prevent the transistor from dying. The current from the IO pin to the base of the transistor should be less than 1.5mA at 3.3V. So assuming the maximum power rating of all IO pins is not exceeded this should be working fine (note: the total current all GPIO pins should be less than 50mA). V+ has to be 5V to drive the relays. The GNDs of the RPi and the relay board have to be connected of course.

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    With the proviso that this board should NOT be used to switch Mains Power circuits directly - the relays are not good enough to provide the barrier between the (European at least) voltages concerned and the low-voltage stuff associate with the RPi... under fault conditions (condensation or dampness, dust etc.) the creepage and clearance distances between the switched contacts on the relays and everything else would put someone touching another part of the Pi stuff at risk of a shock from the Mains. – SlySven Jan 6 '16 at 23:35
  • Yes, @SlySven, that's right. But the question does not imply the switching of mains. – Ghanima Jan 6 '16 at 23:37
  • ☠☠ Just wanted to avoid anyone thinking of it. ☠☠ – SlySven Jan 6 '16 at 23:48

I will probably use a buffer or an array of optocoupler in the middle before connecting something to the Rpi, obviously the cost will increase but at least you save your board everytime you connect any type of defeat hardware, specially with 120/230Vac.
Speaking of optocouplers, they are tested for 2-3-5-7kV isolation.

  • The transistor acts as a simple discrete buffer (single-transistor amplifier). Control circuit and controlled circuit are DC isolated by the relays themselfes. Of course the use of optocouplers would introduce an additional barrier and provide more 'ease of mind'. – Ghanima Sep 4 '14 at 18:04

Yes! There should be no problems.


At the bare minimum I would use socketed optocouplers, and drive the board with a separate power supply. You will never be sure what a failure of the relays can bring to your driver board. If you are rolling your own interface PCB, route a slot between the sides of the optocouplers.

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