I have an auxiliary input unit which is connected to some external PIRs. The idea is that when the PIR triggers (only does so at night), a C-Bus channel switches on and then off again after a timer.

The slight fly in the ointment is that the PIR remains triggered for 60 seconds after the movement ceases. So, I have a very short delay on the timer so the C-Bus group stays on for just a few seconds after the PIR releases.

To achieve that, I have the unit programmed as:

Short Press - Onkey;
Short Release - Retrig;
Long Press - Idle;
Long Release - Retrig;

After 5 seconds, the timer sends an Offkey.

Most of the time this works correctly. The light comes on as soon as the PIR triggers and goes off again just over a minute later. Very occasionally though, the light stays on for ever. The problem is easily cured by walking in front of the PIR when, lo and behold, the light goes off after just over a minute. It is a little inconvenient to have to wander outside at 3:00am to repair the illumination caused by a passing cat!

I have not managed to come up with any logical explanation for the unusual behaviour.

Ideas appreciated,