speedometer

A reliable speedometer is without question very important for model racing cars. They do cost a pretty penny, after all. This article describes how an ordinary bicycle computer can be used as a speedometer that is convenient, accurate and inexpensive.Avid model car fans are naturally enough always interested in the technology and performance of their cars. They would like to know as exactly as possible how fast their model cars actually go, for example so that they can select the final gear ratio for the best performance. Other factors can also be of interest, such as the total distance that the car has travelled, since it is worth knowing how long a car can run on one battery charge or one tank of gas.

Resistors:
R1 = 220kΩ
R2 = 120kΩ
R3.R9 = 10kΩ
R4,R14,R15,R16 = 1kΩ
R5 = 33kΩ
R6 = 3kΩ9
R7 = 270kΩ
R8 = 100Ω
R10 = 470Ω
R11 = 8kΩ2
R12 = 180Ω
R13 = 1kΩ8
Capacitors:
C1 = 100µF 16V
C2 = 100 µF 10V
C3,C4 = 100nF
C5 = 1nF
C6 = 10nF
C7 = 22nF
C8 = 1µF 10V
Semiconductors:
D1 = zener diode 5V6 1W3
D2 = 1N4148
T1,T2,T3 = BC547B
T4 = BC557B
IC1 = 74HC132SO
IC2 = 4017SO
OPTO1 = SFH9201 (Siemens)