This project came about because I got roped into helping to organise a charity running event. The intention was to have a number of people with stop watches and recording times and positions manually as the runners crossed the finishing line. It seemed like a task for a simple timer, one person could hit a button as each runner crossed the line and the time would be recorded and transmitted to a laptop, of course once the idea was in place it seemed to me that a natural evolution would be to display the time.
A reasonably large display was required, the time I have for this project is limited and the cost of large LEDs soon adds up so I bought a cheap LED clock to hack. This clock is branded Kosda and each segment is made up from 13 LEDS, when I opened it for the first time I was pleased to see that the display is mounted on its own PCB and is connected to a controller using a ribbon cable so its a simple task to wire in a custom controller. This is what I have to work with:
I will use a Microchip PIC microcontroller for this project because I'm familiar with them and I have a copius supply of them. The Kosda display has 23 connections to it, these need
to be reverse engineered but its a fairly safe bet that they are all signal lines, common anode/cathode strobes and segment drives. The micro will therefore need to support the following connections:
- 23 data lines
- 1 serial port Tx
- 1 serial port Rx
- 1 reset button
- 1 start button
- 1 'collect time' button
- External crystal 1
- External crystal 2
A 40-pin device should cover the requirements OK, I have plenty of 18F452 devices, these are an old device but will be more than adequate for the task. I may even be able to use an old PICDEM board for the project.
For the data link to the laptop I will use an FTDI based serial/USB converter cable that was acquired for a different project a few years back.