The sensor illumination LEDs are mounted above the track just high enough for the cars to clear, with each LED positioned to shine directly on the sensor below it. The sensor should ideally be mounted recessed below the track so that the light from this LED is the only light hitting it.
Shown below is a detailed diagram of how you would hook up a single LED.
However, instead of using a 100 ohm resistor for each LED, as shown above, you can use just one for the whole string, if you size it appropriately. Use the diagram and chart below to determine the appropriate size.
The +5 volt wire connects to the +5 pin on connector J5 on the main timer board. The Ground connects to the GND pin on connector J5.
| Resistor Size Chart | |
|---|---|
| LEDs | Resistor Size |
| 2 | 27 ohms |
| 3 | 18 to 22 ohms |
| 4 | 15 ohms |
| 5 | 10 ohms |
| 6 | 8 to 10 ohms |
Note that the correct ohms rating depends on the specs of the LED, which may vary. To calculate your own resistor sizes, you can use the Resistor Calculator page. My currently shipping LED's have a voltage of 3.0 to 3.8 with 3.4 typical, and a maximum current of 30mA.
The J5 connector also has the connection for the Ready LED. This LED is hooked up as indicated in the top diagram, except that the current limiting resistor is not used. The appropriate sized current limiting resistor for a standard red LED is included in the circuit on the timer board. Hook the short lead to the same ground pin as the white LEDs, and the long lead directly to the Ready pin on J5.
This is a prewired 4-lane illumination harness with a red ready LED.
This chart is for the older, low voltage white LEDs shipped before Feb 2006. These were rated for 15,000 MCD output, and 20ma at 3.3 volts.
| Resistor Size Chart | |
|---|---|
| LEDs | Resistor Size |
| 2 | 47 ohms |
| 3 | 33 ohms |
| 4 | 22 ohms |
| 5 | 18 ohms |
| 6 | 15 ohms |