L293D chip not working as expected on Arduino Uno R3

I have two L293D chips which are not behaving as expected. My setup is as in the diagram which is attached. Everything seemed to be working fine till I powered the Arduino Uno R3 through the Jack with a 9v battery. using this setup: http://playground.arduino.cc/Learning/9VBatteryAdapter

Chip 1:
Works as expected for about 30 second then stops
Sometimes makes high pitched ‘squeek’[/li][/list]

Chip 2:
Pretty much normal functionality but can move the motors without their separate battery supply

Can I have damaged these chips in any way? How can I test if the chips are damaged? What damages chips? Is my Setup ok?

Thanks for the help,


Robot2.fzz (6.48 KB)

First check the diagram: I hope all the things wrong are just wrong in the pic, not real life. (Like grounds and live from the chip to the wrong rails on the breadboard.)

So either fix all that in real life, or in the pic.


Just wired that way in diagram. Sorry should have checked that over better! I’ve attached the new one.


You blew up your UNO. the 9V should have been connected to Vin, NOT 5V !

Ok, what is VIN? Is the Uno dead or the L293D chip? Blink program still uploads and works...


Zoom in on you Fritzing and look at the last pin on the end of the header, next to the GND pin. (The one labelled " Vin") That's the pin that is connected to the Ext Dc power barreljack that has nothing connected in your Fritzing. If your Fritzing is not a correct representation of how it is wired then please post something that is. According to your Fritzing, the only POWER pins on the arduino that have anything connected are the 5V and GND. I shows the 9V battery pack connected to the 5V L293-16 is the LOGIC SUPPLY INPUT (SEE PAGE 5 of datasheet for Recommended Operating Voltage Vcc1=5V, L293-8 is the Motor Supply input pin . You have 9V connected to L293-pin-16 AND 5V of arduino. You blew the L293 and maybe if your lucky your arduino is still ok but I don't know how.

I don’t think the whole UNO is blown, because it will run blink. How else should I test?
There was a 9v into the jack as in this image. Where can I find out how to correctly wire this?


Arduino seems to be fine when not using the L293D chip. I still don't understand what I did wrong? I have wired it like this (but using the 9v jack not the USB): http://www.instructables.com/id/Control-your-motors-with-L293D-and-Arduino/

Thanks for the help,


Your last Fritzing was wrong and that's all I had to go on until you posted the latest one.

So its its wired as in my last Fritzing it should be fine?

If the last Fritzing is correct and the L293-pin-16 was actually connected to 5V and not 9V and the arduino had the 9V plugged into the barreljack and not connected to 5V then it should be ok.

Thanks for the help. How do I check if my L293D chips are blown? They seem to partially function i.e. work unpredictably.

Thanks, Alex

Those Fritzings are well-nigh impossible to follow. So let me swing it back on you. The attached is a circuit which afaik is good: you compare your circuit to this (the Arduino i/o pins will probably be different).

Your pins 1 and 9, the ENable pins, might not be on i/o pins like I have it; they can be straight to 5V. And of course the motor battery voltage might not be 9 like I show.

Thanks for the diagram, really helpful. I will order a new chip and try again.


alpeace89: Thanks for the diagram, really helpful. I will order a new chip and try again.


You're welcome, but why bother? L293 is old inefficient technology, rather have a look at something better here, for example.

Ok will do, so what attributes should I be looking for in a H bridge?

L293D is perfect for beginners and its about as simple as it gets with a fairly good current rating per channel (1A), meaning it should work on almost all small motors.

Look for the pinout of the l293D, is all over the place on google. Understand what each pin is for and how it works, then wiring carefully without the arduino.

Use 5V or ground signals in place of the arduino on the inputs. You won't be able to change stuff like direction quickly but it sets the foundation that you know the chip works.