View Full Version : l293d problem

11-21-2007, 04:25 PM
i want to interface L293D with uC using MCT2E for protection. However i am slightly confused. According to a 8051 book (by mazidi) , u have to connect 12V to Vcc of L293D. but dont you normally connect +5V? please help.thanks in advance.
The schematic is at


11-21-2007, 04:35 PM
Read the Datasheet!!!

It clearly says VCC1 (the Chip supply) to be 4.5V - 7V max. - that is (recommended. )

But the Absolute maximum rating remains at 36V !! for both VCC1 and VCC2!!

So you can readily connect 5V!

(And it was a bit difficult to read you circuit diagram.) So didnt go though the diagram well.

11-21-2007, 10:16 PM
Thanks allbits... ill read the data sheet next time...

and sorry about the pic... now its better...
here's the link-

thanks again,

11-22-2007, 12:05 AM
It is better to use 5v @ pin 16. This is the logic supply and need not be any greater > than 7v. to keep things in control. Thats a Logic level Vcc and the quiescent current as such is more....

You have to redo your MCT2E connection to the L293d. Connect a pull-down resistor from enable to Gnd.

11-22-2007, 11:47 AM
this might help.....

11-22-2007, 02:01 PM
Thanks a lot docel, saurabh for your replies. by the way what value of pull down resistor should i use? and do i connect the L293D to the same +5V as the uC? because i have read in the previous threads that you have to seperate the power supplies... what do i do?


11-22-2007, 03:00 PM
Some thing like 1k to 4k7 should do. It doesnt really matter, just that there must be a Ov on the enable pin when the MCT2E is off.

The split supply is to differentiate the Logic and Motor voltages. Pin 16 can be tied to the controller.

11-22-2007, 11:00 PM
thanks again....


11-22-2007, 11:39 PM
You're welcome Sinan!
Do let us know how it all worked out.
Good Luck :!: :!:

11-23-2007, 09:42 PM
Sure... I have finished making the PCB design. Will get it made in a week hopefully. But exams coming up now so will have to test it after the exams. Will keep you guys updated. Thanks again everyone.

By the way one guy is charging me 65 paise per sq. cm for high quality single sided design but he needs the gerber file. Is it reasonable? And which software do i use for PCB design. I mean which is accepted by most manufacturers? I am using PCB123 and it does not give gerber file so i cant go that guy anyways... So any better options?

Thanks again

11-24-2007, 10:12 AM
Good Sinan!

The cost is OK. Wonder why only Gerber??
You can try Eagle PCB www.cadsoft.de . Free download and all that if a small pcb.

So, why not try it yourself? It is great to have a self made PCB!!

Just try it. You'll be all the more proud of it!!

Good Luck and best wishes for your Exams and project!!!

11-26-2007, 06:57 PM
Thanks docel... Guess i'll do that...

Had gone to lamington road today. found in one shop (visha electronics) that they do take printouts. Their cost was 50 paise per sq. cm... and they were charging around 150-175 (dont remember the cost exactly) for the postive and negative photo-something... 8O Since i dont need more than one board it wasn't really worth paying that much.

Anyways thanks for all the help. will let you guys know how it goes.


11-27-2007, 03:30 PM
Well, i finally sat down to making the PCB yesteday and guess what! The layout was just a little too big for the copper board. So i decided to draw the layout again by eliminating unnecessary(?) components. but im not sure about it. instead of having four 330 ohm resistors can i have just one like in the schematic below? same for the 1K resistor?


thanks in advance,


11-29-2007, 11:34 PM
:arrow: NO :!: :!:

11-30-2007, 03:25 PM
Thanks docel...


12-01-2007, 12:37 AM
hello, xrayd
Is the pcb pricing you mentioned above is with green mask/ solder mask?

12-02-2007, 12:50 PM
yes... i haven't spoken to the guy firsthand but this is what my college professor told me... i forgot the name of the shop but its in vile parle(E)... if u want i'll find out and let you know the name of the shop....

12-02-2007, 01:39 PM
ya please i am in search of a good economical source.

12-05-2007, 09:15 PM
ok... i got the number...
the guys name is Naveen Shetty and here's his cell phone number-

Do let me know what he says...


12-06-2007, 12:16 AM
This thread is about :!: l293d problem :!:

Now, why is it going off at a tangent about PCB fabrication, etc.,???

There are other similar threads regarding PCBs in the Forum where you can thrash your commercial problems.

These last few posts will be deleted, so shift forums, if you want to continue. Or let me know ; i can splice this topic to a separate thread.

We need to have some discipline in the Forums and you must abide by the Forum rules-- Stick to the Point :!:


12-06-2007, 03:03 AM
sorry!! will remember from next time onward :D :D :D :D

12-06-2007, 01:12 PM
:oops: :oops: :oops: :)

02-22-2008, 12:32 AM
Not a cardinal sin, but...........
Wont you feel nice to see posts connected to a problem in one place? :D
Thing is, people will 'search' for a topic....and find something else!!!