Doubt about the pnp transistor
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Doubt about the pnp transistor

by exapod on Wed Feb 08, 2012 11:55 am

If you use a pnp transistor for switch the npn that drives the leds is the pwm signal inverted? i mean if the pwm of the uc pin is high for 20us the led will be off for 20 us or i am wrong?
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Re: Doubt about the pnp transistor

by stephanie on Wed Feb 08, 2012 2:29 pm

You are correct, when pin 5 is high, the IR leds are off, and when pin 5 is low, the IR leds are on.
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Re: Doubt about the pnp transistor

by exapod on Thu Feb 09, 2012 7:55 am

So if i use the v1,2 software but control only one led with a npn it will not work??
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Re: Doubt about the pnp transistor

by stephanie on Thu Feb 09, 2012 8:42 am

If you want to do that then you'd have to modify the software to invert the signal on that pin. It's not too difficult, just changing a few lines in the main file.

I actually had to do this on my most-recent TV-B-Gone build, not for the IR LEDs but for the visible LED as my build had the visible LED wired to ground instead of Vcc.
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Re: Doubt about the pnp transistor

by exapod on Thu Feb 09, 2012 5:14 pm

Thank you for the help.
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