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Newbie having trouble in relay


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I'm having trouble with a set of relays that I bought. It is the small set that only has the two relays on the board.

http://www.sainsmart.com/relay/arduino-pro-mini.html

I've tried wiring them every way imaginable and they still won't work properly. The only way they will come on at all, is if I put my 5 VDC to the VCC terminal, and they will not actuate with the outputs from the controller.  I've tried them with two different Arduino Uno's. I'm also not sure which is the proper placement for the jumper. I'm not sure what I'm doing wrong. Any help would be most appreciated.

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  • 2 months later...

I went to that site you gave there, and it is not much help at all. I assume one connects this unit to a parallel port, and enlarging the picture I see no transistors, but an opto coupler. They do mention that 20ma is needed, and there is an input for a separate power supply.

So here is a criteria - you need power and you need a positive drive of 20ma to operate the relays.

To test apply power to Gnd and a positive 5v to VCC.

Use a 330 ohm resistor and connect between IN1 and VCC - relay number one should operate, the same for IN2 - relay 2 should operate.

Conversely if the IN1 and IN2 is looking for GND connection then use the 330 ohm between gND and IN1 and IN2.  From this you will know what the inputs require, and you can make up your circuits as specified below to make it work.

That proves the unit is ok (You might need to measure the relay outputs with an ohm meter to see if they are working if you cant hear them operating)

The computer you are going to use needs and output that can supply 20ma at 5 volts. Many outputs do not supply 20ma so one might need to use a transistor, the output line goes to the base the collector goes to IN1 or 2 via a 330 ohm resistor. The Emitter goes to GND that is if the 330 ohm resistor operates when taken to GND.  (NPN transistor)

If the relays operated when the 330 ohm was connected to VCC then a PNP transistor is used Emitter goes to VCC and collector goes via 330 ohm resistor to IN1 and 2.  Any Audio driver transistor can be used, ask your supplier for a Audio driver PNP or audio driver NPN.

Good luck....  Trevcharl

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