View Full Version : ATmega8 pin burnout!!

02-07-2006, 09:45 AM
We are using ATmega8 and L293D to make a bot. The problem we are facing is as follows:
ATmega8 pin15(PB1) pin17(PB3):motor1 input
ATmega8 pin16(PB2) pin18(PB4):motor2 input
there is a 74HC244 buffer in between the microcontroller and the L293DNE
first, we tested if the microcontroller was working according to the code on a breadboard and it was.
when we put it into the circuit, it(uC) works fine so far as the motor supply is not given on pin 8 of L293D.
as soon as the supply is given, the microcontroller pins 15-18 start giving values like 2.7V, 3.1V and stuff like that.
A while later, the pins stop responding totally.
now, when the supply to the motor is removed also, these pins have stopped responding totally to any code whatsoever.
another problem is that when the buffer input is something like 0.63V(due to the erratic functioning of the uC), the output is 2.7V. Why?
Full Schema:
1,9,16 -->> 5V
8 -->> 12 V
2 -->> 74HC244 pin18
7 -->> 74HC244 pin16
15 -->>74HC244 pin14
10 -->> 74HC244 pin12
4,5,12,13 -->> GND
3,6 -->>M1
11,14 -->> M2
1,10 -->> GND
2-->> ATmega8 pin 15
4-->>ATmega8 pin 17
6-->>ATmega8 pin 16
8-->>ATmega8 pin 18
1: VCC via 1Kohm
that describes the ckt.
Please help.

02-07-2006, 01:26 PM
I think u r using same power supply, might be an adapter of 500mA capacity.
Tell about the ratings of the motor.
I think motor is drawing too much current, which cause uC to stop running.
This is due to brown out detection of automatic reset.

I had done same. I used two motors of 250mA,12V. But the uC which i used was atmega8515L which can work from 2.7-5.5V, that created no probs to me and ur uC is atmega8 which won't work at low voltage. I advice u better to use separate power supply for motor and uC,even if u r using battery.
Think if an adapter of 500mA current driving capacity, how can it drive two 250mA(mostly available dc geared motor rating, that to at 12V). If u want u can try for a low voltage by working motor at 9V(7809), but depends on ur application. When i had done the same before, the voltage on motor was about 9.6V(eventhough i used 12V) and uC was around 3.84V(some approx memory). But in that i used one IR LED, Photo Diode, LM324 also with L293D and two DC motor.

Bibin John

02-07-2006, 04:48 PM
the power supply is 2 A 16V... tried common for both ckt and motor and separate also...
the motors are 380 mA stalling current each...
and the uC doesnt stop working, the pin burns out... it stops responding to any program whatsoever later on...
awaiting help

02-07-2006, 04:53 PM
btw we are using ATmega8L whose operating voltage is 2.7 - 5.5V

02-08-2006, 03:34 AM
I bought atmega32l from sunrom.com through online buying. That was my first uC. But PORT C is not working on tht atmega32l. I think same probs with u. Voltage and current ratings are enough. Try to write a simple program to write a value(except 0x00,0xff). Put DDRX=0xff and PortX=0x45. See if the value is reaching on ur port. If not, then that port had burn out.

Bibin John

02-08-2006, 11:32 AM
Yogi you might be having the prob which I had. For my Mega32 also the Port C wasn't working.

Then i went through the datasheet and found that the PORT C is also used for JTAG interface.

So i reprogrammed the higher fuse bits from 0x99 to 0xd9 and turned off the JTAG interface.

Now my PORT C is working !

The prob which Dhruv is facing, I have faced that one too ! And you would be surprised to know my solution. After checking all the connections and finding no one faulty. I simply resoldered the whole circuit on a new board and now the same components worked.

So for this prob I myself never found out what the prob was !