running an 8 station 5V non-JD-VCC relay with external power

Hi all,
first time poster, noob at electronics (and I am older, so please be kind :slight_smile: )

I have received 2 ACTIVE HIGH relays via eB, however, the relay board only has VCC, not JD-VCC.

I am using the board, on one of the relays, to control a 24 VAC sprinkler (for a garden watering system).

I have it currently running perfectly on a Active LOW relay, but really do not like the fact that it can turn on if relay power is on, via JD-VCC, but MicroController has not lowered the GPIO (I am using an RPi).

So, I have done tons of reading and discussing, but can’t get an answer if it is possible to run it with external power only having VCC. The seller states it is, but is not giving specifics.

HEre is the link to the relay: … EBIDX%3AIT

here is a schematic of two possibilities (Please be aware I do not know what I am doing and am asking for advice):

Nether circuits are any good.
Take the lower one and connect the junction between the transistor's collector and 10K resistor to the relay input. Then connect the transistor's emitter to ground.

TY for replying: I am confused - I attached below schematic #2 where I rerouted the transistors emitter to ground.

I don’t understand the 10K junction / collector ton IN1

Currently, 10k is from GPIO to transistors base, does that stay, then rerouting the collector to IN1?

TY for your help!


Do you have a schematic of the relay board?

If the PCB use input opto isolators, you may not need the 1k collector resistor.


LarryD and others,
unfortunately I do not have any schematic to the board - the above link is all I have; unable to find anything more about the relay board.
The parts are sooo tiny!

Even with opto-isolator, would the above, with the 1k, make sense to use with an external PS?


The description of that relay board is useless.
You NEED a circuit diagram if you want to be sure you're doing it right.
Without that, you're basically on your own.

I would try the "active high" setting with a current limiting resistor between the micro and relay input (only grounds shared). And hope that 3.3volt is able to activate the relays.
Otherwise you have to use the level shifters (10k/NPN/1k) you're using now with "active low".

So I would use the second schematic I posted (which is intended for active high) with the transistor as indicated?

Most offerings like this have a resistor in series with the led of the opto isolator.

+5v----VCC----series resistor----anode of opto led------cathode of opto led------terminal strip-------collector of driver transistor OR GPIO pin.

Also, there may be a visualizing LED in the circuit.

There is no opto isolator.
This is a board with IR remote control.

So, without knowing more about the board, does the second schematic appear correct?

So I would use the second schematic I posted (which is intended for active high) with the transistor as indicated?

As said, I would FIRST try if the relays reliably activate with 3.3volt (through a safety resistor).

Connect the relay board to a suitable supply, and try it the relays activate with one AA battery (no micro).
Then try two AA batteries in series (2.5 to 3volt).
If that works, then there is no need for 8 transistors and supporting parts.

Hi, Should be no problem with documentation from the seller that includes several lines of technical information, including this:

fly away to ride the world premiere of Electronic Science and Technology;


What I can see:

  • Those actual relays, same as the ones on THIS: relay board, draw 80mA each. So yes, you DO need an external 5V supply if using this with Arduino.

  • There is no optical isolation, so you need to connect the relay board ground with Arduino/Pi ground.

  • You can pick active low or active high inputs with jumpers on the board. I suggest you pick Active Low, and follow the How-To on that subject HERE: Find the paragraph "IMPORTANT NOTE". and read about Active Low. See the example software sketch.

DISCLAIMER: Mentioned stuff from my own shop...

OP could ofcourse try to control it with IR signals for full electrical isolation.

Ty I had read that article before. I Don't understand why active low is safer - as in my example, I am controlling a sprinkler valve. If the system powers dow, external power goes to relay, but Ardunio does not power on,then the relay would be active low, water would start running uncontrolled?

If the system powers down and the relay board's power stays on ...
Then I would choose active high.

If everything powers ON or OFF at the same time, then it doesn't matter if the relay board is configured active low or high.

Use the COM and NO terminals of the relay to switch the load's power wire. That way, when the relay board looses power, all switched loads will be OFF.

So then, using the board active high, and wanting to use external power to drive the relays, using MC to drive IN1, is my schematic correct?

Sorry ... what is MC?

MC = Micro Controller (in this case a Rpi).

Yes, diagram 1 is correct if you ignore the thick line through the Pi.
But I would not connect it to the Pi unless I knew the threshold voltage and input current.
The relays should reliably switch with 3volt (2x AA batt) on the input, through a 470ohm series resistor.

Ty that being said, keeping the board at ActivevHigh, is the above schematic with extra PS correct?

Define "above".
I was referring to the diagram in post#0
The top one with the thick black line through the Pi.