Hi all,
first time poster, noob at electronics (and I am older, so please be kind )
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.
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.
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".
Leo..
Most offerings like this have a resistor in series with the led of the opto isolator.
Typically
+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.
.
rfeyer:
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.
Leo..
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;
Wow.
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.
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.
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.
Leo..
)
