So I have these relays that I control via digitalWrite HIGH and LOW... I see a light but not enough amperage to trigger.
Huh, just realized they are rated for 65mA, could've swore I got ones rated less... I am pretty unfamiliar with figuring transistors, would I need something special? (3v3 @ ~30mA >> 3V3 @ 65mA) Am I looking for a low collector current? Thanks for any guidance!
No connection diagram or image of the setup, and no code.
How can we possibly help you.
Please read the "how to post" guidelines.
Why did you buy 3volt relays. 5volt relays are common, even for 3.3volt processors.
A 3volt relay draws more coil current (130mA) than a 5volt relay (75mA).
But that current comes from from the relay supply, not from the Arduino output pin.
The load on the Arduino pin is usually about 2mA.
Leo..
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You don't need anything special to drive a relay like the shown in the link. That module comes with the transistor already mounted on it.
Because, Leo, the issue is not the wiring or code, unless the uno can't power the relay? And maybe I posted in the wrong section.And I got logic level relays because at 5v the uno can't provided much current, and was originally going to make part of this project work with an ATTiny. Silly pipe dreams.
Anyway, I guess I was confused between "working current" and "trigger current" for a sec, so you're right maximo, it SHOULD work. Okay, I will draw a schematic, but it WON'T be pretty...
I didn't pen in the grounds, but they are connected. I WAS planning on posting in the project area, after this one issue was figured out. But the relay behavior persists even if nothing else is connected.
Can you elaborate for my novice brain the importance of this? What do I need instead?
If your relay needs 3V and it’s coil resistance is 65mΩ the current need is:
Current = Voltage ÷ Resistance = 3V ÷ .065Ω = 46 Amps
what kind of relay is rated for 46 amps? I don't get it
It's 3V and needs 3mA to trigger, what am I missing?
You don’t understand.
The coil will draw 46 Amps from the Arduino 3V power supply.
This is obviously a huge error in the documentation.
The coil might be 64 or maybe 640 ohms but definitely not 64 milli ohms.
64 ohms gives
3v / 64 = 46mA
640 ohms gives
3v / 640 = 4.6mA
Ah, thanks for catching me up. But how do we know that THAT is the only wrong info face palm
So the former value, too much for the arduino
The other, it should work? Seems like it's 64 ohms, and the rest of the doc is bunk?
Hi,
Can you please post some images of your relays?
So we can deduce what its characteristics are.
Thanks.. Tom... 
If you already have purchased the relay, you can covert it to 5v operation by adding a series resistor to the coil to drop 2v.
What resistance do you measure on the relay coil ?
Give us a close up image of the actual relay board.
Bed time here, Australia can take over.
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Thank you for your help Larry!
I dont see that
Each relay requires "about" 65mA for its control. So you need a simple driver to control it from the arduino pin which cant support that current.
You ALSO need a 3V - 3.3V supply that can provide enough current for the relay coils. I cant se that in the spec, but the 3V pin on the uno is "almost certainly" not able to do so.
Of the circuit board? It looks the same as the listing on amazon, but I notice mine says srd on what I take to be the optocoupler. Important?
Thanks, I was wondering about this too... 'almost certainly' is enough for me to try an independent power source tomorrow...
So, what is the proper relay to use with Arduino? I really should've come here first, you guys are too helpful.
Typical charactreistics for a songle relay - note 3V coil takes 120mA
You can then use the realys you have simply by adding a transistor as a driver - as shown here (replace motor with relay in& out, dont need diode or capacitor, single npn transistor eg bc108 )
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How... would one go about measuring the coil resistance? I got nothing with the multi-meter from IN to GND with the relay powered or not.