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power led from uC pin, opamp or BJT?

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danjel

Member
I have an atmega168 driving 4 different buffered outputs (voltage follower opamp with single rail supply powered from gnd and +5).

I also want to put leds on these four outputs to show their logic status.

Should I put the leds+current limit resistor to the uC pin (before the opamp buffer?

OR connect it to the opamp buffer output?

OR connect it to the uC output via a BJT?
 

kchriste

New Member
Forum Supporter
If the outputs are digital, then you should use a digital logic buffer and not an OpAmp. The outputs may not need any buffering at all if they can supply enough current for the LEDs and whatever else they are driving. Whatever method you use, resistors should be added to limit the LED current.
 

danjel

Member
The digital outs are actually 5V gate outputs for an analog synth. They should be relatively low impedence sources as a result. Would a normal logic buffer do the same thing?

I thought using an opamp as a voltage follower and powered by the analog supply rail would help remove noise being sent out the gate outputs. It also makes sure there is no direct connection to the uC controller in case someone patches the wrong thing into the gate outputs.
Maybe this is the wrong strategy?


Also the leds I am using are very low current so I guess and led + current limiting resistor would be fine.
 

kchriste

New Member
Forum Supporter
Yes, a normal logic buffer would be OK. If you really want to isolate the analog supply, including the ground for noise & safety purposes, then you could use optoisolators. With good circuit design, optos can be avoided.
 
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