|Circuit and PCB designed by Phil Townshend c. 2002
The function of this circuit is very simple. As a car passes or an LDR sensor, it starts a timer in 1/100ths of a second. The next time it passes the sensor, the display freezes displaying the lap time. the following lap the timer resets and the process is repeated so the timer times alternate laps.
In this model, there were two identical timers, one for each track.
There are 2 versions avaiable, a 3-digit and 4-digit version. Since the displays are not multiplexed and are on all the time, a considerable amount of current is drawn. If all displays were on, displaying 88.88seconds, the following current would be drawn:
4 displays x 7 segments @ 20mA per segment = 4 x 7 x 0.02 = 0.56Amps.
So with the 2 displays combined, this model draws a maximum current of over 1.1Amps!