strange breadboard/power probelm

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v1r05

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hi

ive been using my breadboard for a long time now but in the last two days i couldnt get any learning done because of a strange problem in the power or the breadboard i dont know how to tell you all this, the circuit is simple just a microprocessor 16f628a set to blink all leds on portb and thats it ive done this before on that same breadboard and it works good but this time it dosent the problem is that the circuit dosent run unless you touch any of the positive potential lines !

ive also done the circuit on an old breadboard ive had, i even fabricated the power supply circuit(7805 +3 cap) in a stripboard with no luck just getting an led that turns on and off very fast i dont think you can notice that on the clip

to understand better take a look at the video ive shot to see for yourself and try to explain or suggest a soultion

here is the link for a photo of the breadboard

and here is the video
 

You only have but a few parts there... why dont you solder them together so you aren't worrying about intermittent connections with those lousy breadboards. That's my suggestion.
 
i did atleast some of them ive soldered the power supply circuit on a stripboard with just the micro and two resistors and an led in the bread board.

also ive used that breadboard before and it works perfectly.

what do you think the problem is ?
 
v1r05 said:
i did atleast some of them ive soldered the power supply circuit on a stripboard with just the micro and two resistors and an led in the bread board.

also ive used that breadboard before and it works perfectly.

what do you think the problem is ?
Click to expand...

Since the power supply is presumably a low impedance, touching it should not cause malfunction of the circuit behavior. Therefore, it is something else. #1 on my list would be intermittent connection. When you touch a wire, you may be briefly disconnecting it from the conductor buried in that plastic breadboard. When the holes on those things get used alot, they tend to "loosen" up and start causing intermittent connections. Try re-wiring all your power supplies to different holes and see if it fixes it. If that ends up being the problem, throw that thing out and spend your money on a soldering iron & solder.

let us know how it goes.
 
Are you using the internal oscillator because i cant see an xtal in the photo?

Have you missed any connections out?
 
A few things:
1. Is MCLR enabled? It should be tied high with a 10K resistor.
2. What are you using that 10uF cap for? It looks like it's tied to pin 1. If you want a decoupling capacitor try 0.1uF and connect it from Vdd to GND.
3. Unused pins are set as outputs?

Mike
 
@Optikon: ok just tried moving the components arround and to another breadboard(which sucks) and still the problem remains, am not a big fan of stripboards although i liked the pic-pc rs232 interface i created on a stripboard works smoothly.

@ziggy_dan: no, not using an oscillator and no havent missed any connection.

thanks a lot for trying help guys
 
thanks mike

yes MCLR is enabled and getting high through a resistor (not 10k dosent matter or does it ?)

yes its tied to MCLR pin just thought if it would help but nothing happened.

what do you mean, should i connect "all" unused pins to GND ?

the thing that i dont get is these two boards were functioning absolutely fine a few days ago and then they just dont want to work anymore !! really really frustrating
 

Did you check all your wiring again? I distrust those stripboards so much (can you tell?) that I would pull each wire out and re-seat it again.

*IF* after that, you are sure of the electrical connections, then perhaps one of them is still wrong. If you have re-wired it recently and then it stopped working, go back to the point where it stopped and check the connections you recently made to make sure you didnt plug one into a close but wrong hole. A schematic can be correct but the wiring job may not reflect the electrical connections.

Is there a blinking signal on the output of your PIC? Whats the value of the LED current limit resistor? Just make sure its not something goofy like that (burned out LED)

Did you change something in the PIC code? Maybe there is a bug there..
 
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Hi,
Last time I was having this problem too, just a 8 pins PIC. I checked everything I found that the PIC was not working and it was working previously. Just because I didn't add current limiting resistor in series with the LED, so I burned 2 PICs
 
yes its tied to MCLR pin just thought if it would help but nothing happened.
Click to expand...
If you are talking about the 10uF cap, then you are on the wrong pin. MCLR is on pin 4 and NOT on pin 1!!!!
As noted by Blue and Up, you need to straddle the 16F628 with a 0.1uF cap so that the cap is as close to the PICs power pins as possible:
 

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I've seen similar behavior when I've accidently left LVP (low voltage programming) enabled

Make sure it is off in the config word, something like this

__CONFIG _CP_OFF & _WDT_OFF & _BOREN_OFF & _PWRTE_ON & _INTOSC_OSC_NOCLKOUT & _MCLRE_ON & _LVP_OFF
 
@kchriste : spot on !!! works perfectly now, i cant belive how stupid i am i was sooo confidant that i didnt do any wiring error but yet i did ? !!! 40pin pics messed my mind up they are the ones with MCLR on pin1.

not gona do that mistake ever again.

thanks all for your help.
 

Wiring errors happen ALL the time! You will make that mistake again so get used to checking & double checking your work. It happens to everybody. You will get better over time though. While you are improving your wiring skills, ditch that lousy stripboard.
 
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