[Dr_C2]

Apologies for bringing an old thread back to life. It’s now 18 months since the experimental work on ‘Smart IR LEDs’ was completed, conclusions drawn and the work reported here.

First the name ‘Smart IR LED’ is used because the device is an IR LED with its own tiny microcontroller onboard.

The finalised version of the Smart IR LED uses a ATtiny 6 pin microprocessor, a precision crystal oscillator and an opto isolator. The latter is to accommodate voltage level shifting between the host decoder and the Smart IR LED.

So to recap:

The Smart IR LED can be connected to any SSD decoder or oXigen decoder to translate the decoder IR strobe output from whatever mark/space ratio is in use … to … one of the 36 proprietary IDs of System-D.

As the ATtiny chosen for this work doesn’t contain any user programmable SRAM, the Smart IR LED is pre-programmed with a fixed ID at the point of program flashing (an obvious limitation … but all is fair when testing feasibility).

So what input signal does the Smart IR LED require?

The answer is any of the following:

1/ Any of the six Hornby SSD IDs.
2/ Any of the six Slot.it SP15c/d IDs.
3/ Any of the Slot.it oXigen wireless decoders’ IR strobes either when emulating SSD IDs 1-6 or in O2-SSD hybrid mode.
4/ A simple logic high or logic low (for SCX-A compatibility).
5/ A standard R/C receiver output (pulse length modulation around 1ms mid point).

Method 5 was added thanks to a kind recommendation from Drifter2.

These Smart IR LEDs are quite small (I believe I showed the dimensions earlier in this thread), they exist and they function correctly.

As an interesting point of detail, my most experienced test driver found an earlier version of the firmware locked after about 70 minutes of continuous driving (without any de-slots). This was traced to an overflow of a timing register inside the ATtiny - easily fixed once diagnosed :)

Thanks for reading!

c