data loss, PIC get crazy!?

[bananasiong]

Hi,
I'm using two PIC12F629A with two receivers of my RF module and they worked fine a few days ago. Yesterday, I tested them again (without reprogramming them) with the RF module, they didn't work, both the PIC's!!! That IC has only 8 pins, so I'm sure the connection is correct. And I found that the PIC is getting hot.
Then I remove from the breadboard and reprogrammed it (with the same .hex file) and plug into the same hole of the breadboard, then one worked and the other PIC is burned.
How come this can happen? Has anyone had this problem too?

EDIT: Before they're reprogrammed, the ammeter from the PSU showed 1 A when it is turned on, then I quickly turned it off and removed the RF module, turned it on again, the current was still 1 A. So that must be the PIC's problem. It is okay after being reprogrammed.

Thanks

 

[Sceadwian]

Sounds like you didn't put a current limiting resistor on an I/O that needs it and shorted the supply to an I/O pin.
In order to figure out where the fault is you're going to have to post a complete schematic of the entire circuit you have so far.

 

[bananasiong]

Sounds like you didn't put a current limiting resistor on an I/O that needs it and shorted the supply to an I/O pin.
In order to figure out where the fault is you're going to have to post a complete schematic of the entire circuit you have so far.

I didn't include the current limiting resistor for the LED, is it the main reason? If it is, now only I realize how important it is. Then I should always put the resistor for good practice.

Thanks

 

[Sceadwian]

Oh yeah, you HAVE to use a current limiting resistor on an LED, and many other components and data interfaces. It is just a diode after all, there's no limit to how much current it will let through, there is however a limit to how much current the I/O pin and the LED itself will let through before burning up.

 

[bananasiong]

Thanks for that, I'll use a 220 hm: for that.
In my college, we have done a lot digital experiment which LED is being used. But we never use resistor with the LED, even from the output of 555 timer as well (not CMOS type).
If this didn't happen to me, I won't realize how important it is.

Thanks

 

[Sceadwian]

If you're in college for digital electronics and you don't know why a resistor needs to be used on an LED to limit current something is seriously wrong with your college, or you've not been paying attention.

 

[bananasiong]

If you're in college for digital electronics and you don't know why a resistor needs to be used on an LED to limit current something is seriously wrong with your college, or you've not been paying attention.

No way, I pay attention all the time. The schematic given in our study material don't have the current limiting resistor, for example egg timer circuit. There is no even a bypass capacitor at pin 5 of the 555 timer. I think I learn more from here

 

[Sceadwian]

Simple knowledge of a diode's V/I curve will easily tell you that you need a current limiting resistor. If this isn't taught in school....

 

[blueroomelectronics]

The 12F629 has a built in 4MHz osc, it's accurate enough for flashing an LED.

You'll also need a 0.1uf decoupling cap across VSS & VDD

Lots of 12F629 info here.

**broken link removed**

 

[Pommie]

Maybe the LEDs used in college are the 5V ones - IE with the current limiting resistor built in.

Mike.

 

[Hero999]

Some LEDs even have a built constant current IC and will work from 4.5V to 15V.

 

[Ayne]

Oh it means a simple LED can burn a PIC!!!

I think the problem is not LED cuz if LED is the problem then it should be demaged one I/O port, not the whole PIC...

I think the problem is, u have applied more than 5 volts to PIC VCC...

 

[bananasiong]

The 12F629 has a built in 4MHz osc, it's accurate enough for flashing an LED.

You'll also need a 0.1uf decoupling cap across VSS & VDD

Lots of 12F629 info here.

**broken link removed**

Yes I have.

Maybe the LEDs used in college are the 5V ones - IE with the current limiting resistor built in.

Some LEDs even have a built constant current IC and will work from 4.5V to 15V.

Is this kind of LED existing? I mean with the resistor built in? I don't think we have this in our college.

I think the problem is, u have applied more than 5 volts to PIC VCC...

No, I'm sure. Definitely not more than 5.1 V

 

[mas]

For the Input ports ..

should the input voltage be connected across a resistor ???

I don't use a resistor for inputs !!!! .. Will this make mt pic burn or damage ??

 

[Nigel Goodwin]

For the Input ports ..

should the input voltage be connected across a resistor ???

I don't use a resistor for inputs !!!! .. Will this make mt pic burn or damage ??

As you don't give any idea what you're trying to do it's impossible to say, but the inputs are normal CMOS inputs. PIC's are very hardy devices, you have to do pretty stupid things to damage them (and even then they often survive).

 

[Hero999]

Is this kind of LED existing? I mean with the resistor built in?

Yes, some LEDs have resistors built in, some even have a constant current IC so the LED draws the same current regardless of the voltage across it.

I don't think we have this in our college.

I don't know, ask the lecturer.

 

[bananasiong]

Yes, some LEDs have resistors built in, some even have a constant current IC so the LED draws the same current regardless of the voltage across it.

I don't know, ask the lecturer.

They don't know much about the lab, I should ask the lab technician. But he has resigned recently, so nobody take care of the lab anymore
But I'm sure that normal cheap LED's are used over here. I've experienced once, the polarity is opposite

 

[Souper man]

I suggest you use a 16 DIP resistor package to limit the current going through the curcuit. They work pretty good.

 

[bananasiong]

I suggest you use a 16 DIP resistor package to limit the current going through the curcuit. They work pretty good.

16? PIC12F629 has only 6 IO pins and I'm using only one pin for the LED

 

[Souper man]

I was reffering to when i used 2 of them for a BS2 project