Doubt about the pnp transistor

Get help and show off your TV-B-Gone kit!

Moderators: adafruit_support_bill, adafruit

Please be positive and constructive with your questions and comments.
Locked
User avatar
exapod
 
Posts: 15
Joined: Tue Jul 12, 2011 1:58 pm

Doubt about the pnp transistor

Post by exapod »

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?

stephanie
 
Posts: 295
Joined: Sat Dec 11, 2010 1:17 am

Re: Doubt about the pnp transistor

Post by stephanie »

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

Re: Doubt about the pnp transistor

Post by exapod »

So if i use the v1,2 software but control only one led with a npn it will not work??

stephanie
 
Posts: 295
Joined: Sat Dec 11, 2010 1:17 am

Re: Doubt about the pnp transistor

Post by stephanie »

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

Re: Doubt about the pnp transistor

Post by exapod »

Thank you for the help.

Locked
Please be positive and constructive with your questions and comments.

Return to “TV-B-Gone Kit”