# IR LED circuit

Discussion in 'The Projects Forum' started by shapirotechnics, Jul 14, 2008.

1. ### shapirotechnics Thread Starter New Member

Jul 14, 2008
3
0
I am beginning a simple project, it's basically a circuit containing an infrared LED and a momentary switch. Optimally, I would like to use a AAA battery as the power supply.
I have a very limited knowledge of electronics, so I need help determining how the circuit will work.

These are the specs on the parts I purchased.
--IR LED--
Forward Voltage: 1.2 V
Forward Current: 100 mA

--Switch--
Contacts rated 0.5A at 125VAC/250VAC

Will this work in a circuit with a AAA battery? What resistors will I need (if any)?

Thanks in advance for any and all help (and if anyone has the time/desire, I wouldn't mind knowing what all this information means)

2. ### Audioguru Expert

Dec 20, 2007
11,217
1,331
The LED needs a resistor in series to limit the current to below 100mA. The AAA alkaline cell will have a voltage that is 1.5V when it is new but its voltage will drop to below 1.2V quickly (about 4 hours) then the LED will not work.
If the resistor is 3.9 ohms then the current is about 70mA when the battery cell is brand new. Then it will dim for 4 hours.

3. ### shapirotechnics Thread Starter New Member

Jul 14, 2008
3
0
Thanks for the quick response. So for the LED to work the voltage has to be ABOVE 1.2V and the current has to be BELOW 100mA? That's very helpful, so what about the switch?

4. ### Audioguru Expert

Dec 20, 2007
11,217
1,331
Yes for that LED, the voltage must be above 1.2V and the resistor limits the current to below 100mA.

Just about any switch will work with less than 100mA.

5. ### shapirotechnics Thread Starter New Member

Jul 14, 2008
3
0
Awesome! Thanks for all the help... this was one of the quickest, most helpful and most friendly forums I have ever posted on!