The circuit uses a PIC micro-controller and runs off 5v. The circuit contains a voltage regulator to accomodate this.
Download circuit diagram and PCB details
The following table shows the frequency of pulses produced against speed based upon a 26" diameter wheel, (2metres per rev.)
|
SPEED m/s
|
SPEED km/h
|
MPH
|
FREQUENCY Hz
|
|
2
|
7.2
|
4.5
|
4
|
|
4
|
14.4
|
8.9
|
8
|
|
6
|
21.6
|
13.4
|
12
|
|
8
|
28.8
|
17.9
|
16
|
|
10
|
36
|
22.4
|
20
|
|
12
|
43.2
|
26.8
|
24
|
|
14
|
50.4
|
31.3
|
28
|
|
16
|
57.6
|
35.8
|
32
|
|
18
|
64.8
|
40.3
|
36
|
|
20
|
72
|
44.7
|
40
|
|
Reed connection details:
|
The case was vacuum formed from 2mm polystyrene and the legend produced from acetate. Connection to reed switch used a 3.5mm jack plug/socket.
The reed switch was secured using cable ties to the front forks. The magnets were purchased from a cycle shop and were the screw on type to the spokes. When connecting the wires to the reed switch take care as the connections protruding from the reed switch are easily broken off fracturing the reed. A suggested way of connecting to the reed is shown left. Cover the reed and wires with heatshring sleeving, a couple of times over to help protect it. When securing it to the front forks take care not to put cable ties around the glass body of the reed or its connections.
|
