Home

Automation HAT / pHAT

I've connected an LED to an output, but it's not lighting up, what gives?

The outputs on Automation HAT and pHAT are driven by what's called a Darlington Array - this is a chip with a transistor pair for each channel which allows a small current to switch a much larger one.

The Darlington Array does not supply power, however, but rather acts as a switch between your load (be it an LED, a motor, a stepper) and Ground.

This means the long leg of your LED should be connected to 3.3v or 5v (via a suitable resistor) and the short leg should go into the "input". When the "input" is switched on, it will connect the LED to Ground.

What sort of accuracy can I expect from the Automation HAT / pHAT ADC?

We go really in depth on this topic in the forums: https://forums.pimoroni.com/t/automation-hat-accuracy/7252

But the long and short of it is that accuracy varies and you can expect an average of +-2%. This is due to quantization on the ADC itself- which is only 11bit -combined with error introduced by the tolerance of the resistors used. Automation HAT and pHAT use 120k and 820k resistors to divide the 25.85 maximum input voltage down to the 3.3v that the ADC can tolerate.