About automation pHAT using outputs



( Refering to this post. )

I have some troubles with the Automation pHAT to understand the outputs use. I read the Gadgetoid post (in the link above), yes, but where to connect the power source? I don’t know to observe any current from these outputs.

I tryed to load 5V in the input.one and set the output.one.on() with no success…
I beleve these outputs works like transistors or i am wrong.

Thanks a lot from France. ;-)


Yes, they are- in fact- Darlington Pairs. See: https://fr.wikipedia.org/wiki/Transistor_Darlington

Picture them as a switch (a push button perhaps) that sits between your load and ground.


Gadgetoid, I appreciate you answering me so quickly on Sunday night.It is very respectful.

Ok it is an output that is turned on or not. I still do not understand how and where to plug my power supply. When you talk about load, is it my component for example?

With no surprise, the output is High i measure 0,5V between himself to the ground.

Anyone can give me a pict or schéma in real use of the product please.

Phil, I love everything you do.


The simplest way to understand what’s happening is this:

a. Turn an output off and measure between output and 5v
b. Turn that output on and measure again

For “a” you should read ~0v, for “b” you should read ~5v.

All of the outputs are basically ground connections, which you can turn on and off.

To power an LED, for example, you would connect the positive side- anode- of the LED to 5v (via a suitable resistor of course) and the negative side- the cathode- to the output on Automation pHAT.

When the output is turned ON it allows current to flow through it, to ground, completing the circuit. When it’s turned off, it acts like an open switch, and no current will flow.

You could also think of it as a single NPN transistor. It works pretty much the same way, but the Darlington Pair is used to boost the amount of current that can be handled.


Hum… Ok!!! ^^

Here is a constructive answer. I just could not imagine it is allowed to connect the 5V to an output… For me, the output was necessarily upstream. I will try as soon is possible.

And about 24V maximum please, is juste only the Darlington pair capabilities?

Thanks you!


It works. Thanks again for explain to me.

Link to a demo video on Twitter.


The ADC channels are also 24v tolerant (actually up to 25.85v) and use a voltage divider to divide the 0-25.85v input down to 0-3.3v.

The inputs are protected by a 470k resistor and a 3.3v diode.