Computing stuff tied to the physical world

A simple RF pulse scope

In AVR, Software on Jan 10, 2009 at 23:45

Here’s a simple way to analyze RF pulse trains, as emitted by simple 433/868 MHz remote controls. A receiver for the proper frequency band is required, as well as some Arduino board connected to USB.

The code is a sketch which picks up all 0/1 transitions (i.e. presence/absence of the radio carrier) and reports the elapsed time between each transition:

Picture 1.png

The radio signal is tied to the analog comparator (pin 7), and the timer is set to count in 8 ┬Ásec steps. This rate was chosen to allow for pulses up to 2 msec.

The data is sent as a stream of bytes. Values 2..255 correspond to pulse durations of 16..2040 ┬Ásec. A “0” is sent for longer breaks, a “1” is sent if the data was not transmitted fast enough over USB, i.e. an overrun. Note that “0” values are only sent once, i.e. when there is no signal no bytes are sent to the USB interface.

On the computer side, all sorts of software could be used/written to analyze these pulse trains. I used Tcl for a one-off analysis of KlikAanKlikUit remotes operating at 433 MHz, though it would be really neat to have some sort of logic analyzer GUI or web interface added to this.