I mentioned in this thread a custom power switch board that I designed for controlling smoke units and electrocouplers with a DCC decoder. I threatened to post some details eventually, so here goes.
The board is a simple 2-channel MOSFET power switch board. It has two independent control channels, so it can be used for heater/fan control for a smoke unit, or for powering a pair of front/rear electrocouplers. It uses a p-channel MOSFET, so it is naturally 'logic compatible' with decoder outputs (see the linked thread for some discussion on that). It is very fast, so it's PWM compatible, and incorporates freewheel diodes for use with inductive loads.
Here is the schematic for the board:
Here are the parts I used:
The connections to the board are as follows:
- In1/In2: Input signals from the decoder. One or both may be used.
- Out1/Out2: Outputs to the heater, motor, or coupler coil.
- Vdd: Regulated DC supply, typically 5-6V. (Not DCC from the track - see the other thread for discussion of rectifiers and regulators.)
- Gnd: Return to the regulator ground. Returns from the loads also get wired up here.
Here's a pic of a couple of the assembled boards:
And here's one wired up for a smoke unit for recent install I did:
The red/black leads are the 5V power and return from the regulator. Pink and yellow are the signal lines from the decoder. The red and yellow connectorized harnesses are for the smoke unit heater and fan. I reused these from the original harnesses.
The same board and wiring can be used to power a pair of electrocouplers as well. The physical assembly would be identical. The only difference would be in the configuration of the decoder, which I discuss here.