LocoNet 16-Way Block Occupancy Detector

To implement signaling on my layout I first need to be able to be able to detect block occupancy. So my next project has been a LocoNet Block Occupancy Detector. I decided to make a 16-way device as that made efficient use of the available I/O pins on a 28-pin Atmel ATMega88/168 device. A while ago, I managed to get about a 100 of the VT-5 Current Transformers. These have been used by others to make block occupancy detectors, based on Rob Paisley's - Block Occupancy Detector For DCC.

Initial tests show the detector to be reasonably sensitive and able to detect a 5k - 10k resistive load with 1 turn of the track feed wire through the current transformer. With 2 turns, it was able to detect a 20k (2 x 10k) resistor and even just my finders across the track. However, with 2 turns, when I applied a short to the first block the second block also triggered. This is probably due to how I have mounted the current transformers, which is convenient for mounting on Veroboard because of the way the copper tracks run, but not good in keeping the magnetic flux from one transformer from being detected by adjacent current transformers under heavy loads - oh well that's what prototypes are for...

The design has the following features:

The Schematic is here
The Source code is in the CVS Archive but I have not got a schematic done for it yet.

Here are some more photos of the prototype:

Completed LocoBOD-16 prototype

Top of the Veroboard showing links and component placement

Underneath showing cuts in the copper tracks

Close-ups of the components for each current transformer input

Close-ups of the components for each current transformer input

Close-up showing the link under the IC socket linking the two GND pins

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