WiFi Infrared transmitter/receiver

Picture The espirp WiFi Infrared transmitter/receiver is intended to automate devices that are controlled via infrared signals.

Infrared signals

There are hundreds of existing IR protocols, and more are likely to be created by equipment manufacturers in the future. To be able to handle as many of these IR protocols as possible, the espirp was designed to be flexible regarding the protocols it supports, and new protocols can be easily added by the user without requiring a firmware update. To that end the device has been designed around the IRP specification, that was developed by John Fine. An IRP definition is a very compact way to describe nearly any imaginable IR protocol. It looks something like this (example is for RC5): Adding a new IR protocol is simply a matter of entering the IRP definition on a web page. IRP definitions for many protocols can be found online.

To improve noise immunity, as well as battery life, IR protocols generally don't simply use an on/off IR signal. Instead a carrier at a fixed frequency is switched on and off to transmit the bits of the IR signal belonging to the function assigned to a remote control button. The espirp is able to transmit IR signals with a carrier frequency between 33kHz and 57kHz. The frequency of signals that can be received depends on the IR receiver installed. Most common IR signals use a carrier frequency of around 38kHz. For this reason the schematic shows a 38kHz receiver; a TSOP1838. It is possible to use a different IR receiver, as long as it works at 3.3V and the pinout matches the TSOP1838: 1 = OUT, 2 = GND, 3 = Vs.


The device is designed to primarily communicate via MQTT, but it also provides a web interface to simplify experimenting with IR signals.

To be able to easily place the device in a location where it has a straight line of sight toward the devices it is intended to control, it connects to the home network via WiFi.

Once up and running, the device supports Over-the-Air (OTA) updates. An update can be started using the web interface and via MQTT. The latest available firmware version is: 3.0

Hardware components

The device can be built using mostly commonly available components. Nonetheless, gathering those components from different sources can be cumbersome. One particularly difficult part to get a hold of in small quantities, is a piece of infrared acrylic plastic.

Fortunately, I found the Nodo shop happy to add an ESPIRP kit to their product range. The kit contains the circuit board, components, and an enclosure, including an IR front panel and back panel with the required hole for the micro USB plug. Note: The Wemos D1 mini is sold separately.