This is the C revision of my model speed control project and its current state is work in progress.

Model Railroad Speed Control (Revision C)

At this point in time, the revision C schematic consists of a scanned in schematic:

If you can read and understand the scanned in schematic -- more power to you. Over time the scanned in schematic will be transfered over to on-line schematics below. For now these are just the revision B schematics.

The following diagrams exist:

Block Diagram

The block diagram of the entire circuit (no change from revision B):

Timing Circuit

The timing pulse generator (no change from revision B):

Power Drive

The power driver circuitry:

Only minor changes are coming here. We're switch from TIP41 and TIP42 transistors to TIP31 and TIP32 transistors. One of the traces is being rerouted to simplify the PCB layout. The fuse is being moved next to the power input. Also, we're ditching the relay because we figure people who really want to control the direction with a relay will put the relay off board. Lastly, we'll be adding a capacitor to smooth out the signal a little and a diode to clamp the negative voltage spikes.

Control Amplifier

The control amplifier circuitry:

There are two major changes here. First, we're going to switch over to a cheaper analog switch -- the CD14016. The CD14016 is not as good as the AD7510, but it is much more available. We will compensate for the poorer quality of the CD14016 by putting three of them is series to reduce resistive losses.

The next major change is that we are replacing the CLM50 with an opto-isolated MOSFET -- something like the H11F1QT (that may just be a Digikey part number.) The CLM50 works fine, but it is difficult to obtain. We wanted something that is likely to be available for a while.

Linear Momentum

The linear momentum control:

The linear momentum circuit is getting a simple switch to enable and disable momentum. The amount of momentum will be settable via a potentiometer. We're giving up on the standard brake for now. The emergency brake will remain for a while.

Manual Setting

The manual setting stuff has been removed for revision C.

Power Supply

The power supply:

The power supply is getting more room for the filter capacitor. The protection fuse is going right after the diode bridge.

There is no PCB artwork yet.