USB powered relay for arduino

[kondenado]

Hi Folks,

Long story short I need the Arduino to control some sensors and power a fan. (12v or 5v). I don't need a lot of power (its just to ventilate some plants to remove humidity).

I cant use a MOSFET or Arduino relay shield as I need the pins for the sensors.
I cant use a normal relay as I don't want to make "custom wires" for fire hazards. (I could rip a USB cable plug it into a normal relay and that's all) but I would rather not.

So I was wondering if there is any better option such as
a) USB-powered relay, so instead of "feeding" the relay with a + and - wires you just plug a USB cable.
b) You can power a USB relay with an Arduino/raspberry pi power source

Any hints?

[xfpd]

Do not power a relay with an Arduino.

You probably can find relay modules with screw terminals for the ripped USB cable if you are worried about soldering.

For comparison, your tea kettle and toaster use screw terminals for connecting power.

[TomGeorge]

Hi, @kondenado

@kondenado

I cant use a MOSFET or Arduino relay shield as I need the pins for the sensors.

What model Arduino are you using?
Can you please post a copy of your circuit, a picture of a hand drawn circuit in jpg, png?
Hand drawn and photographed is perfectly acceptable.
Please include ALL hardware, power supplies, component names and pin labels.

If you use a 5V supply you can power a 5V Arduino controller and a 5V relay off the same source.

@kondenado

I cant use a normal relay as I don't want to make "custom wires" for fire hazards.

So how do you envisage connecting up the relay or switching device to the controller?

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Thanks... Tom..

[gilshultz]

@kondenado

custom wires" for fire hazards.

You do not need much power but you also state the above. Explain what you are doing.

[sterretje]

Which Arduino? An Uno has 20 signal pins. You need one for your fan. Leaves you 19 for sensors (in practice 17 if you don't want to use pins 0 and 1).