SPAX is a model-railroad DCC signal booster. It is a well-known hardware construction from FREMO model railroaders club in Germany. This repository contains firmware and PCB design for a new processor PIC12F629 which is supposed to replace original PIC12F508 SPAX v2 processor without changing whole SPAX pcb.
This is a low-cost solution for eliminating old-processor disadvantages. For future expansion (RailCom etc.) whole new SPAX should be designed.
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Weird shortcut detection The old processor measured current as analog signal on digital CPU input. This caused bad detection sometimes. The new processor reads analog input and uses internal comparator.
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Short shortcut-restore time The old processor indicated shortcut when e. g. cars with larger capacitors were put on a track. When new processor detects shortcut, it leaves max current for a longer time – 20 ms. This is enough time for capacitors to charge.
Manufacture 12F629.brd PCB and replace DIL8 old processor with SMD new
processor on the board.
Track power supply is restored after 200 ms, 400 ms, 800 ms, 1200 ms, 1200 ms, ... after overcurrent is detected. This is long-enough time for SPAX cooler to cool-down stabilizer and H-bridge.
H-bridge ensures that shortcut current will never be more than 3 A.
First 3 tests for overcurrent-restore allow only 5 ms of max current, all next tests allow max current for 20 ms.
- Red LED = not generating DCC on output
- Green LED = DCC on input
States:
- Green: generating DCC to track
- Red: DCC on input present, but shortcut detected
- Yellow: DCC not on input
- hardware: Jan Horacek
- firmware: Michal Petrilak, Jan Horacek
The firmware and PCB design is distributed as opensource project under Apache License v2.0.