LEDs
Most LEDs work pretty much the same way. Standard package is the T1-3/4. LEDs
want 5-20 mA of current (If) running through them. Current runs through the LED
from anode to cathode. Cathode is marked by the short lead and/or a notch or flat
on the case. Always place a resistor in series. When active, LEDs have a forward
voltage drop (Vf). Here's some Vf/If data for an ordinary LED connected to a 5
V supply through a series resistor. The 330 ohm configuration is recommended.
| Series Resistor
| Vf
| If
|
| 100 ohm
| 2.2 V
| 27 mA
|
| 150 ohm
| 2.0 V
| 20 mA
|
| 330 ohm
| 1.9 V
| 9 mA
|
You can run two LEDs straight off a single Stamp pin. Wire the LEDs in series
and add a series resistance. Two 330 ohm resistors wired in parallel work nicely.
To drive more LEDs off a single Stamp pin, wire in parallel and turn on and
off via a transistor. For more than 4 LEDs, use a separate battery supply.