Boiling PIC

[GatorGnet]

I setup one of my breadboards with a LED, 7805, and a 16F628a. I wrote a quick blinking program(random patterns) and programmed the pic. Verified the code then installed the pic on the board. When I apply current(12v-->7805) the led starts to run its pattern but with a very slow rate and the pic becomes boiling hot. What could be causing this?

Schematic:
**broken link removed**

PM_USED			EQU	1

	INCLUDE	"16F628A.INC"

RAM_START       		EQU	00020h
RAM_END         		EQU	0014Fh
RAM_BANKS       		EQU	00003h
BANK0_START     		EQU	00020h
BANK0_END       		EQU	0007Fh
BANK1_START     		EQU	000A0h
BANK1_END       		EQU	000EFh
BANK2_START     		EQU	00120h
BANK2_END       		EQU	0014Fh
EEPROM_START    		EQU	02100h
EEPROM_END      		EQU	0217Fh

R0              		EQU	RAM_START + 000h
R1              		EQU	RAM_START + 002h
R2              		EQU	RAM_START + 004h
R3              		EQU	RAM_START + 006h
R4              		EQU	RAM_START + 008h
R5              		EQU	RAM_START + 00Ah
R6              		EQU	RAM_START + 00Ch
R7              		EQU	RAM_START + 00Eh
R8              		EQU	RAM_START + 010h
FLAGS           		EQU	RAM_START + 012h
GOP             		EQU	RAM_START + 013h
RM1             		EQU	RAM_START + 014h
RM2             		EQU	RAM_START + 015h
RR1             		EQU	RAM_START + 016h
RR2             		EQU	RAM_START + 017h
_PORTL           		EQU	 PORTB
_PORTH           		EQU	 PORTA
_TRISL           		EQU	 TRISB
_TRISH           		EQU	 TRISA
#define _l1              	_PORTB_4
#define _l2              	_PORTB_5
#define _PORTB_4         	 PORTB, 004h
#define _PORTB_5         	 PORTB, 005h
	INCLUDE	"TEST.MAC"
	INCLUDE	"PBPPIC14.LIB"


	LABEL?L	_go	
	HIGH?T	_l1
	PAUSE?C	0012Ch
	LOW?T	_l1
	PAUSE?C	0012Ch
	HIGH?T	_l2
	PAUSE?C	0012Ch
	LOW?T	_l2
	PAUSE?C	0012Ch
	HIGH?T	_l1
	PAUSE?C	0012Ch
	LOW?T	_l1
	PAUSE?C	0012Ch
	HIGH?T	_l2
	PAUSE?C	0012Ch
	LOW?T	_l2
	PAUSE?C	0012Ch
	HIGH?T	_l1
	PAUSE?C	0012Ch
	LOW?T	_l1
	PAUSE?C	0012Ch
	HIGH?T	_l2
	PAUSE?C	0012Ch
	LOW?T	_l2
	PAUSE?C	0012Ch
	HIGH?T	_l1
	HIGH?T	_l2
	PAUSE?C	0C8h
	LOW?T	_l1
	LOW?T	_l2
	PAUSE?C	0C8h
	HIGH?T	_l1
	HIGH?T	_l2
	PAUSE?C	0C8h
	LOW?T	_l1
	LOW?T	_l2
	PAUSE?C	0C8h
	HIGH?T	_l1
	HIGH?T	_l2
	PAUSE?C	0C8h
	LOW?T	_l1
	LOW?T	_l2
	PAUSE?C	0C8h
	HIGH?T	_l1
	HIGH?T	_l2
	PAUSE?C	0C8h
	LOW?T	_l1
	LOW?T	_l2
	PAUSE?C	0C8h
	HIGH?T	_l1
	HIGH?T	_l2
	PAUSE?C	0C8h
	LOW?T	_l1
	LOW?T	_l2
	PAUSE?C	0C8h
	GOTO?L	_go

	END

 

[Hero999]

What's the value or R?

The LED is connected backwards so it won't light.

There should be a 100nF capacitor across the supply pins of the IC.

 

[GatorGnet]

R1 is 100k, only one I have at my desk tonight. The schematic is a little off, I just did it to show what I have done. The led lights okay(a little dim due to the 100k though).

 

[ericgibbs]

hi gator,
The LED is drawn the wrong way around, this will not cause the over heating.

Measure the +5V on the PIC.

Also whats the rest of the circuit.?

 

[GatorGnet]

I wasn't paying attention when placing the led on the schematic. It even does it when I just apply the current to the pic with nothing hooked to the pins.

And my multimeter is fried!(some user had it on the wrong setting when testing some high voltage...) My new one is in the air from Hong Kong. Could the 7805 be faulty and over powering it? Would that throw the timing off too?

 

[Hero999]

100k is much to large for an LED, I'm surprised you can see it.

It could be the LM7805 but you won't know until you measure the output voltage. If the 0V pin on the LM7805 isn't connected then the output voltage might be much higher than 5V (possibly 10V) which could damage the PIC.

 

[Nigel Goodwin]

You also have the absolutely essential capacitors missing around the 7805 - so you've no idea what voltage might be coming out of it, or how big the oscillations from it are.

But even more likely is that you've connected the PIC the wrong way round, when they get absolutely red hot - I've got one with my fingerprint burnt in the top! .

 

[Vizier87]

whoa nigel.. PICs with your natural sig on it.. I'd like to buy that!

 

[Gayan Soyza]

See my one..........

 

[Nigel Goodwin]

whoa nigel.. PICs with your natural sig on it.. I'd like to buy that!

And it still works fine!

 

[GatorGnet]

I've done this test before without caps and it worked okay. I know its not right though.

I replaced the 7805 with another one and the overheating stopped but the pic didn't do anything this time(led isn't lighting up).

 

[Gayan Soyza]

Did you measure regs output voltage before plugin?
Did you connect regs +5V terminal to the 14th pin?
Did you connect GND terminal to the 5th pin?
Did you check whether your LEDs working good?
Did you change your resistors?
Did you program the PIC?

 

[Hero999]

Perhaps the PIC is fried?

Anyway, the other LM7805 was clearly not working I recommend you chop all the leads off and throw it away so you can never use it again.

 

[Gayan Soyza]

Perhaps the PIC is fried?

Anyway, the other LM7805 was clearly not working I recommend you chop all the leads off and throw it away so you can never use it again.

You must throw far away

 

[GatorGnet]

Did you measure regs output voltage before plugin?
Did you connect regs +5V terminal to the 14th pin?
Did you connect GND terminal to the 5th pin?
Did you check whether your LEDs working good?
Did you change your resistors?
Did you program the PIC?

Yes
Yes
Yes
No - only one at hand. All my supplies are someone else.
Yes, even reprogrammed it just to check.

I will see whats up when my new meter gets in. The first 7805 must have issues.

 

[Hero999]

Bad components and meters aren't worh the grief, throw them out!

I think you should at least mark the LM7805 as bad before you test it - stick a label on it or put a cross on its back using a marker pen.

I've kept bad components before and wish I hadn't because they destroyed other components or I've wasted time fault finding. As in this case an LM7805 is much cheaper than an MCU, it's certainly not worth the risk.

I also recommend discarding your old meter or at least marking the settings which don't work. I had an old meter which wouldn't work on AC voltage so I marked it, that way I didn't forget if I wanted to measure the mains for example. I don't have the meter any more, I gave it to a friend who needed a meter for measuring the voltage of a lead acid battery he'd hooked up to some solar panels.

 

[Vizier87]

You must throw far away

I always did that but it always rebounded into toolbox. then I have to extricate it again? Pur-lease. So then the vicious circle keeps on perpetuating itself until I do a spring cleaning of my toolbox!!