There is no USPS pickup on Monday Feb 15th, 2016 because of President's Day. USPS orders placed after 11am EST Fri February 12th will go out Tuesday February 16. UPS orders will ship as normal.

Doubt about the pnp transistor
Moderators: adafruit_support_bill, adafruit

Please be positive and constructive with your questions and comments.

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?
exapod
 
Posts: 15
Joined: Tue Jul 12, 2011 1:58 pm

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.
User avatar
stephanie
 
Posts: 295
Joined: Sat Dec 11, 2010 1:17 am
Location: Canada

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??
exapod
 
Posts: 15
Joined: Tue Jul 12, 2011 1:58 pm

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.
User avatar
stephanie
 
Posts: 295
Joined: Sat Dec 11, 2010 1:17 am
Location: Canada

Re: Doubt about the pnp transistor

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

Thank you for the help.
exapod
 
Posts: 15
Joined: Tue Jul 12, 2011 1:58 pm

Please be positive and constructive with your questions and comments.