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AD5PE
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Posts: 66




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« on: August 26, 2004, 04:08:52 PM »

I'm working on a friend's IC-211 2m all mode.  It has (among other things) a backlight out behind the s-meter.

Two questions:
Does anyone know of a source for the correct bulb?

Alternatively, does anyone know how to mod it to use a white LED in place of the bulb?

Thanks,
Jay
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KB1LKR
Member

Posts: 1898




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« Reply #1 on: August 26, 2004, 11:44:16 PM »

What's the voltage applied to the bulb? With that (and assuming it's at least 5V) you should be able to calculate the required resistance of current limiting resistor to deliver rated (desired) current thru the LED. Don't forget a white LED has perhaps a 3V junction drop -- check the data sheet for the desired LED.

For example if you have 12V, an LED that requires 20mA w/ a junction drop of 3.0V then you need to get 20mA at 12V-3V=9V of drop across your current limiter so you need a 9V/0.02A = 450 ohm, 1/4W or 1/2W(9V*0.02A=0.18W) limiting resistor. A 470 ohm would be close enough.

http://www.icom.co.jp/manual/external/transceivers/IC-211.pdf  indicates that the meter lamps *are* LED's however.
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AD5PE
Member

Posts: 66




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« Reply #2 on: August 27, 2004, 10:48:51 AM »

KB1LKR,

you said:
For example if you have 12V, an LED that requires 20mA w/ a junction drop of 3.0V then you need to get 20mA at 12V-3V=9V of drop across your current limiter so you need a 9V/0.02A = 450 ohm, 1/4W or 1/2W(9V*0.02A=0.18W) limiting resistor. A 470 ohm would be close enough.

Thanks - that's exactly what I needed!  It is indeed a 12V bulb in there now, at 60mA, but the white LED's from R$ are 3.6V @ 20mA

Much appreciated.
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