Debounce HAT

A six-channel, fully isolated and debounced input HAT for Raspberry Pi

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The Debounce HAT provides six channels of opto-isolated, debounced digital inputs to a Raspberry Pi-compatible single board computer (SBC). All inputs accept 3 - 24V with arbitrary polarity and can alternatively be connected to open-collector outputs or mechanical switches leveraging the on-board isolated 5V supply.

Debounce HAT render; bottom, v1.2

Compatible with a Range of Systems

The Debounce HAT is intended to be used with Raspberry Pi systems, but it can also be used with compatible systems as well as in other configurations (including stand-alone, ignoring the HAT functionality).

Surge Protection

If you’re looking to interface a Raspberry Pi system (or compatible) with external inputs like switches, relays and similar, while preventing any potential issues due to electrical surges on these inputs - this is the HAT for you. In addition, the Debounce HAT fully debounces any inputs and eliminates the need for any debounce software routines.

Features

Electrical Specifications:

  • 6 opto-isolated, uncommitted inputs accepting +/- 3..24 V, with transient voltage protection.
  • Isolated DCDC for 5V 400mA supply for sensors and switches (4 kV DC isolation rating).
  • 8 A rated power terminals for easy 5 V supply to additional devices.
  • Active input protection with reverse and overvoltage protection (configured for 5.9 V cut-out).
  • Ideal diode voltage drop below 200 mV at 3 A.
  • >2.4 mm clearance between logic and isolated sides (PE floating).
  • Spark gaps between input pairs.
  • Spark gaps between input pins and PE.
  • Spark gaps between isolated power and PE.
  • Marked pins for input testing.

Mechanical Specifications:

  • 16 mm PCB stacking height (defined by 2x20 pin 0.1" header).
  • Raspberry Pi - compatible mounting hole pattern.
  • PE connection via 4.8 mm spade connector and M3 mounting point.
  • 3.5 mm pitch terminal block for power in / pass-through (ø 0.2-1.5 mm² / 24-16 AWG).
  • 2.5 mm pitch terminal blocks for isolated power and signal (ø 0.2-1.0mm² / 22-16 AWG).

Typical Applications:

  • Digital inputs with ESD protection
  • Mechanical switch / interlock inputs
  • Isolated sensor interface
  • Isolated DC voltage sensing

Documentation

Backstory

Debounce HAT was born out of necessity. We were implementing a switch detection circuit to determine the state of a door lock etc. in a room. This required a debounce circuit, but the prototype showed the need for a fully opto-isolated circuit to protect against ESD. During winter time, a static charge could be transferred via the metal door handle by a person touching it courtesy of walking on carpet.

We realized that this generally useful input protection and debounce board did not exist in HAT version, so we developed Debounce HAT into this 6-channel version in the hope that others may find it useful as well.

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