Loco Controller PCB Design

By Iain MacDonald 2020-05-21•

It’s a task I’ve been putting off for a while. I’d designed the schematic a few weeks ago with the general sense of the different modules and feature I’d like on the control board that will go inside the locomotives to control the motor and lights. I have a couple of prototypes running around the layout so I’m confident in the overall design but the task of squeezing everything into such a tight space was quite daunting.

I pleased to say that I’ve finally got it to a state I’m reasonably happy with. There were a couple of design iterations but this is the one I’ve ended up with so far.

The ESP8266 is mounted on the underside. The three pins top-left are temporary and only needed once to flash the Micropython OS onto the chip. Updates to the running code can be provided over-the-air. The big round capacitor on the left and the chip directly below it are for motor control. The tiny 6 pin chip below that is a pair of NPN transistors for controlling accessories such as lights. The large 4 pin chip to the right is a bridge rectifier ensure the board gets the correct polarity from the track. the 8 pin chip to the right of the capacitor and large inductor to the right of it is to derive a 3.3 V power supply for the ESP8266. The board connects to the loco through the 8 pins at the bottom which follow the DCC NRMA 8 pin plug layout. The pads at the top of the board are power and and i2c bus for future expansion.

I’ll send these boards off for manufacture and let you know when they arrive.

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