These are brief notes on an IR receiver designed for use in my To the Birdhouse geocache1.

It is essentially a clever Vishay detector chip which receives a coded signal embedded on a 40kHz carrier, then amplifies it. All of the audio information is encoded on the transmitted signal.

[The Receiver] 2

Desiderata

As discussed above3 the detector will be built by people who might have very little experience of building electronics. Accordingly the components in the design all look different to reduce the chances of someone e.g. confusing resistors of different value. Two different resistors are used in this circuit, but different power-ratings make them physically quite different.

Schematic

[Schematic] 4

There is little say about the circuit.

Sensor

The sensor has significant output impedance, and setting R2 to 110kΩ was chosen to feed about 1V into the op-amp.

Op-amp

The op-amp isn’t critical: indeed although the schematic calls for an OP-07, I managed to find a cheap source of NE5534s and used them instead. Either way, it is configured as a unity-gain buffer.

Assembly manual

The manual is produced from some hacky Haskell code, which isn’t really fit for public consumption. Do contact me if you’re interested though.

[Schematic] 5

The reference to ‘The Bloomsbury Group’ is related the geocache puzzle: please ignore it.

Design Files

All the design files can be downloaded from GitHub6. The electronics was designed with KiCad. Random bits of Haskell and python were used too.