Last month, we published the circuit details for the Programmable Ignition Timing Module and its companion Ignition Coil Driver Module and described their operation in some detail. The various input trigger circuits (points, reluctor, Hall sensor, optical, etc) were also described.

LCD Hand Controller

That just leaves the LCD Hand Controller Module. Its circuit is shown in Fig.7. It comprises an LCD module, a 4017 decade counter (IC1), a DB25 socket and several pushbutton switches. This unit connects to the main circuit via a standard DB25 RS-232 cable.

Signals from the microcontroller in the Programmable Ignition Timing Module drive both the LCD module and IC1. IC1 has 10 outputs and each output independently goes high in sequence as it is clocked at its pin 14 input. A high at the reset (MR, pin 15) sets the "0" output at pin 3 high.

Each output connects to a switch. When a switch is closed, it pulls pin 9 of the DB25 socket high whenever its corresponding output on IC1 is high. This allows the microcontroller (in the Ignition Timing Module) to recognise which switch is closed.

The LCD is driven using data lines DB7-DB4. The display readings are entered via the data lines and are controlled via the EN and RS (Enable and Register Select) inputs.

Note that the data lines and the EN & RS lines are all connected to ground via 330W resistors. These resistors allow the LCD module to be driven without the signals being corrupted by interference from the car’s ignition.

Finally, trimpot VR1 is used to adjust the display contrast.