LED Issue
LED Issue
(OP)
I have a micro and sinks the current to a 3.3 V LED via 220 ohms to turn it on. It works but as soon as I put my scope probe on the LED (micro side) the LED doesnt turn on. What can cause that?
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RE: LED Issue
RE: LED Issue
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RE: LED Issue
-AK2DM
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"It's the questions that drive us"
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RE: LED Issue
Dan - Owner

http://www.Hi-TecDesigns.com
RE: LED Issue
put a .1uf cap on the output and micro was not able to drive the led circuit. It tried to...drove it low for 200ns but went back up.
The ckt:
3.3VCC -----R----led----Micro (PIC16F724 port D)
RE: LED Issue
Dan - Owner

http://www.Hi-TecDesigns.com
RE: LED Issue
Gunnar Englund
www.gke.org
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Half full - Half empty? I don't mind. It's what in it that counts.
RE: LED Issue
Your reported symptom seems to be directly opposite of what one might expect, since most micros have fairly robust sinking capability, so loading the output should simply make it harder to rise (turn off).
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RE: LED Issue
Keith Cress
kcress - http://www.flaminsystems.com
RE: LED Issue
Glenn
RE: LED Issue
itsmoked-- what can be causing it in the software?
RE: LED Issue
Mike Halloran
Pembroke Pines, FL, USA
RE: LED Issue
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RE: LED Issue
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: LED Issue
TTFN

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RE: LED Issue
A most common one is this:
The pins DEFAULT to being AIN pins. You may think this doesn't matter because they also state that when set to an OUTPUT it will BE AN OUTPUT. But then PIC's crappy read>modify>write system means that a subsequent 'read' can screw up the 'modify>write' which happens every time you write the pin (every second in your case).
See here:
If you've correctly de-AIN'd your pin then I offer this as a possible problem.
Keith Cress
kcress - http://www.flaminsystems.com
RE: LED Issue
Earth calling perts. Come in perts!
What did you find?
Keith Cress
kcress - http://www.flaminsystems.com
RE: LED Issue
still trying to figure it out. We have 6 leds that get driven from that port on the mico. We noticed that when we drive all the leds on that port to 0 and then turn on the ones we want, it works.
RE: LED Issue
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RE: LED Issue
How is a schematic going to help with a firmware issue?
Keith Cress
kcress - http://www.flaminsystems.com
RE: LED Issue
TTFN

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RE: LED Issue
PICs are pretty funky..
Keith Cress
kcress - http://www.flaminsystems.com