Arduino Nano - Turn ON relay

I’m having problem to turn on relay with Nano.
When the Nano output pin is HIGH, I’m getting 4.69V on it.
I’m thinking that output current making me that ‘problem’ because it’s too low to activate solenoid coil.
(please correct me if I’m wrong)

So, I thought that I can use transistor between Nano and relay, like this

I can’t find any datasheet for my relay, and I need info about his resistance (or power), so I can calculate current that I need to activate coil.

I’m using this 8 channel 5V relay:

Any tip will be helpful…

Did you look at the dataasheet of your 8 relay module? If the picture is indeed what you have, then it has already all those components. The input is opto-isolatoed, which means you simply connect you Arduino output through a 330 ohm resistor (or so) and then to the relay board.

Yes, this relay module on picture is exactly like one I have.
I have no problems to run it with Mega (without using resistor), but Nano can’t run it. That’s the reason why I thought that output on Nano hasn’t enough current to activate relays coil.
I will try today with resistor, like you said.

Another question for the same thing - can I run approximately 30-40 LEDs (low power - 20mA) with Nano, using principle with NPN transistor(right type calculated), like is shown on picture in first post, but without using relays?

Or something like this, with paraller connected LEDs?


Well, if I look at the datasheet for the 2N3904 it states a maximum Ic of 200mA. So no...

If you replace it with a darlington that can handle more current you should be fine.

I gave that picture just to show 'wiring', I saw that 2N3904 has Ic only 200mA. I thought maybe to use for example 2N2222, but to divide LEDs to 4-5 outputs. So I will have 4-5 outputs, every output will have 2N2222, and then group of 5-6 LEDs.

Is that better way, just to 'unload' one output and place all on 4-5 outputs?

Electronically it doesn't matter if you have 1 output or 4-5. As long as the supply current of the output isn't above it's nominal value (Max 20mA I believe...).

Every Transistor has an amplification factor, called current gain or hFE. For example, if the current through the base is 1mA and the hFE is 100, the transistor can sink 100mA in the collector. But there are darlington transistors with an hFE of over 1000.

But reading the 2n2222, it can sink 1A on the Ic, and have a hFE of 100 to 30, so your safe with that one.

Everything is clear now! Thank you guys.

I am confused. According to this page - found by a rough google search for your board's possible specification - - the wiring on the board is an optoisolator to start with. All that needs to trigger the relay is enough mA to light the LED (a few mA). Even the Nano should be able to turn on the optoisolator. But how do you power the relay board? Note that it needs to supplies - one for the positive of the opto-LED, and one for all the relays (with a potential 800mA if all relays are to be on). You can use the same supply if you do not need opto-isolation.

Of course, if this relay board comes in several variations - with or without isolators and transistors etc - then the above may be totally irrelevant.