breadboarding

Hello all
I am working with a Pic 16f628A, and can program it ( albeit I am primitive). I have a problem now where I am using the development board and writing a simple "Blink" program to flash an LED on Port RB0 and it works perfectly, until I breadboard it. When I put it on a breadboard, the LED will flash for about 15 to 20 seconds and then stop. When I turn the power off to the breadboard, the LED resumes flashing for about three seconds as the unit powers down, and then ceases. Then I can power up the breadboard again, and the LED flashes again for 15 to 20 seconds before stopping. Anyone have any thoughts on why the LED stops? The only hardware in my circuit is the PIC, an LED, and a 470 ohm resistor.

reset/mclr pin no pullup?

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Originally Posted by richard

reset/mclr pin no pullup?

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...or possibly Watchdog Timer nipping your butt. Somehow it sounds like you are getting a Reset condition, or maybe a Brown-Out. Check your VDD supply voltage when it quits. If it isn't what you want (especially if it's below about 2.5 volts), you are getting a Brown-Out Reset Hold condition.

You should have a 4.7k (up to 10k) pull-up resistor on MCLR to prevent inadvertent hardware Reset. In your CONFIGs, turn WDT (Watchdog Timer) off. You can do this at program time with PBP.

Since it works on the Dev Board, you have something (or lack something) not the same as the Dev Board. Do you have a capacitor on the power supply to your PIC? Data sheets suggest a 0.1 uF cap RIGHT AT your VDD-to-VSS pins.

Hope this points you in the right direction.

I agree to all of the above responses.
And I do very carefully ohm out all of the connections on a bread board before inserting a chip and before power-up.
Its not uncommon to forget something or get something wired wrong.

Plugin breadboards suck, they are more trouble than the time they save. Make a PCB (or stripboard) with your goto PIC device and add stuff you want to try out on daughter boards, kinda like the boards Mikro Click boards. Often you'll find if your using things on breakout boards (thank you again Arduino for the super cheap modules) you just need a bit of stripboard and a connector.

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The only hardware in my circuit is the PIC, an LED, and a 470 ohm resistor.

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decoupling capacitors are missing !!!

the " magic " one : 0.1/0.22 µF as close as possible to the supply pins of the Pic , and a " reservoir " one say 100/220 µF in the vicinity ...
add to that ... be sure of your MCLR pin ... ( or to have disabled it ! )

But it's right : These chinese breadboards are pure crap ... ( MCP 47 ... i.e. )

the only one I found quite acceptable is a 40 ( 50 ? ) years old genuine " Lab 500 " one. but not exactly cheap. :rolleyes:

Alain