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Scarr said:Hi,
Is there any issues with driving a OPB710F LED directly from a I/O PIN of the Atmega168 without a limiting resistor? I want to drive it at it's MAX power (50ma)
Thx
shaneshane1 said:the LED would probably have a voltage drop of 2.6 to 3.6V and the output is likely to produce more than that
Brian Hoskins said:The OPB710 is an infra-red LED and phototransistor housed inside one package. The IR LED has a max forward voltage drop of 1.5V so a resistor will be required for that reason, if not to limit current as well. 50mA is a lot to draw from a Microcontroller so a driver will be required anyway.
My feeling is that if you connected the IR LED directly to the output pin of a Microcontroller, it probably wouldn't light at all. It would try to draw too much current, which would drop the output voltage below the required forward voltage drop of the LED. It might even destroy the Micro.
Brian
shaneshane1 said:didnt know it was infra-red LED, as for the 50mA been alot for a microcontroller is that common for all?
my PIC can draw 800mA at any given output X8 is that common among PIC's?
Brian Hoskins said:800mA per output? At 5V, that's 4W per output pin. Are you sure??
Brian
Brian Hoskins said:Ahhhh, so now it is clear where your confusion is coming from. Your project board does indeed supply 800mA per output - via a darlington driver IC. The PIC itself is probably rated at 25mA per output.
Brian
Ya shaneshane1, your Picaxe PIC is a 16F88. Standard max output per pin is 25ma.shaneshane1 said:yes i just confused the hell out of myself then, for a second there i was thinking that the PIC was outputing 500mA to my servo motor, but the power for the servo comes from a different supply, and i just use the output for the signal.
Scarr said:Hi, just thought I'd re-post this as my post had a mind of it's own) and I didn't get a reply to my last post.
I was thinking about using a PIN to "sink" the current, put 5v on Anode and sink cathode via AVR PIN, as it can only sink XXma I thought I would not need a resistor or if I put a resistor on it would note drive it sufficiently?
Scarr said:OK get the message, your saying use one anyway
But I don't understand if the PIN can only sink 40ma then is this not just like a limiting resistor, how can it possibly damage the LED unless it was a fauly PIN/MCU, if you still say "use a resistor" what size should it be? bearing in mind my I want to drive it at 50ma? 82R (43ma) or can I get away with 68R (52ma)