View Full Version : A weird Problem with L293D

09-12-2012, 01:00 PM
Hi All i was trying to make a simple robot. I am just a hobbyist but not novice so I Used 4 small DC motors for differential driving (I couldn't find suitable castor so using 4 motors instead of 2 also motors on each side are in parallel).(Motor details : free running current = 100 mA Stall Current 600 mA)
Here is my circuit explained.
I have a 12 v 1.25 A power source (SMPS). Now i use a 7805 to get me 5 v for all the logic pins of L293D. and i put 12 V to its VCC2.
Now i simply wanted to test if my bot is running straight, so i programmed Arduino borard with 4 pins as output keeping 1high 2low 3 high 4 low. This i connected to L293D's input pins
I have connected all the grounds together. And i have done no mistakes in Circuit.
Now when i try to power this automaton it jerks and stops (wheels are not touching the ground i.e bot was suspended in Air). I mean i had given 5 second delay from when the code starts to output. but as soon as motors start my entire circuit seems to flicker and my Arduino board restarts.
Also i had a 10 micro farad capacitor at 5 V 7805 to act as bank.

Few deliberate mistakes from my side
1. L293D --- ok i have 2 motors at each channel so net stall draw could be more than 1 A. but i was just testing its not final design also motors were Geared so they would be on stall for very very less time.

Now what I conclude from this and possible solution from my side :
1. I think i got poor 12 v supply its not able to provide instant energy required for motor.

Either change SMPS (say 12 v 3-4 A ) or use bigger capacitor say in milli farads to store more energy as Bank.

I had checked only voltages in my circuit while trying yesterday and couldn't continue with current as i had office today :(

So if you can find any other fault please reply also add your suggestions.

09-12-2012, 02:57 PM
Get a proper Multimeter and check current and voltages , your power supply seems insufficient.

If you have a Osciloscope lying around hook it up and set some triggers , you will see if voltage is falling causing brownout etc.

09-12-2012, 03:08 PM
Sadly i don't have Oscilloscope, my college days are over :( ... I have my trusty multimeter though. Ya i too thought i am getting a brown out. and as this is not laboratory power supply I am going to get a more powerful supply.
Will post what happens.

09-14-2012, 03:59 AM
Yep it was faulty power supply. Got a new one working like a charm... :)

02-21-2013, 12:50 AM
Yep it was faulty power supply. Got a new one working like a charm... :)

Dude can u plz upload the circuit diagram, i'm having the same problem !!! 've connected L293d to ATmega16. I'm using 12v 1A adaptor to power up L293d...do i need to change the adaptor ?