Question

Simple PIC circuit. LED Flash program

Asked by: ross13

I am trying to set up a simple circuit that flashes a light using a PIC16F627 (print screen 1). This is my first project and is really my hello world program.
The program itself runs ok on my velleman test board but I have tried to set up my own circuit and believe that is where I am failing .
I have tried removing the led from the circuit and replacing it with a multimeter which shows the voltage go from 4.5v down to zero but as soon as I replace this with the led it stays on constantly.
Please see print screen 3 for the set up of my circuit.
I would be very grateful if someone could provide some assistance as there is probably something that I am fundamentally doing wrong.
I was going to upload a photo of my circuit but its too big. Please let me know if this would be useful.



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Asked On
2009-03-07 at 15:22:35ID24209340
Topics

Embedded Hardware

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Hardware Components

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Programming Languages

Participating Experts
2
Points
500
Comments
2

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Answers

 

by: nobusPosted on 2009-03-08 at 04:13:36ID: 23828806

i think you should put a driver transistor on the output of the chip, to supply the current for the LED

 

by: gallymimusPosted on 2009-03-29 at 12:38:56ID: 24014161

You don't need a drive transistor.  Depending on how your code is written the output might not be toggling when you have the LED hooked up because it is going to limit your output voltage of RB0 to approximately 0.7 to 2V depending on the LED.  Remember an LED is a diode and after your reach the threshold voltage it looks like a short circuit.  What you need to do it to put a resistor in series with the LED to limit the current and allow RB0 to rise to it's full voltage.  Try a 1k resistor to start.

Also, you should always have a 10k resistor from MCLR to +5V to prevent any issues or spurious resets

20120131-EE-VQP-002

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