GX-TXT IR Remote Tester

The GX-TXT IR Remote Tester is a small experimental instrument designed to verify the operation of infrared remote controls while also allowing their transmitted signals to be studied directly.

The project began with a deliberately simple goal: to use an IR photodiode and an analog signal chain built mainly with BJT transistors, without relying on an integrated IR receiver that would hide much of the signal behavior. This makes it possible not only to check whether a remote control is working, but also to observe how the received signal is amplified, processed, and converted into the voltage that determines when the indicator LED turns on.

The circuit sensitivity is adjustable, and its response depends not only on the amplitude of the received signal but also on the duration and number of IR bursts. A hold network on the HOLD node converts the received activity into a slowly varying voltage that controls how long the LED remains on. This made it possible to experimentally characterize the relationship between equivalent photodiode current, sensitivity setting, number of pulses, maximum voltage reached at HOLD, and the duration of the visual indication.

An important part of the development was initially carried out using a virtual photodiode, designed to generate known and repeatable currents. This made it possible to compare the LTspice simulation with the real circuit under controlled conditions before moving on to measurements with a real photodiode and actual remote controls.

With the GX-TXT-v3 version, the project reached a dedicated PCB, with test points designed to monitor the main nodes of the signal chain. Measurements at the VIR node showed that the photodiode signal retains enough information to directly observe the IR carrier, reconstruct MARK and SPACE intervals, and even experimentally identify the transmitted protocol. Dedicated GNU Octave scripts were also developed for these analyses to process CSV files exported from the oscilloscope.

The GX-TXT is therefore intended to be more than a simple “tester that lights an LED”: it has gradually become a small experimental test bench for studying IR reception, analog amplification, thresholds, time integration, and remote-control protocols. The articles collected on this page document the entire development process, from schematics and simulations to PCBs, real measurements, and the software tools used to analyze the signals.