I am mystified on powering a LED strip w/pwm

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ckigar
 
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I am mystified on powering a LED strip w/pwm

Post by ckigar »

I built this:

http://www.adafruit.com/blog/2013/03/29 ... pberry_pi/
on a Perma-Proto Raspberry Pi Breadboard PCB.. and it sure looks to me that everything is properly wired up. I added MOSFETS for a total of 8, with the intent of controlling 8 separate LED strips (single color) via PWM (using the Adafruit 16-Channel 12-bit PWM/Servo Driver - I2C interface)
When I attached a LED strip.. nothing. I touched the contact to the PWM output 0 and got a blink, dim but definitely output from the PWM servo_demo.py.. I touched the end to the ground side of the MOSFET and got bright LED (apparently all 12v).. but the center pin.. nothing. It's like the MOSFETS are not switching. This is the case over several channels. I realize I may not have included some key piece of information, but I have examined this guy until going cross eyed and it looks correct.
I could have laid this out better, live & learn.
I could have laid this out better, live & learn.
small.png (1014.67 KiB) Viewed 235 times
Any tips on trouble shooting? My LED strips are cut pretty short, so do not draw much but I wouldn't have figured a resistor would be required for the output of a transistor

Chip Kigar

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adafruit_support_mike
 
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Re: I am mystified on powering a LED strip w/pwm

Post by adafruit_support_mike »

I can't quite tell from the photo: do you have power connected to the VCC pin or the V+ pin?

VCC provides power to the chip itself, and by extension the PWM row of output pins.

V+ connects to the terminal block at the top of the breakout and the V+ row of output pins. It doesn't connect to the chip though.

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ckigar
 
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Re: I am mystified on powering a LED strip w/pwm

Post by ckigar »

Thank you, that was EXACTLY the issue!

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adafruit_support_mike
 
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Re: I am mystified on powering a LED strip w/pwm

Post by adafruit_support_mike »

Glad to hear it's working for you. Happy hacking! ;-)

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