L293D Motor driver issue - please help!!

Hi all,

I have designed this L293d motor driver for my Arduino and I’m having big problem with the circuit. Well, problem is that my motor (connected to M1) works even without motors power supply which is supposed to come through Pin 8 of L293D and GND, it seems to me that the IC is drawing all the power through the regulator. Because the LM7805 regulator is getting hot after few seconds. Well, I guess that is the only problem I am facing right now. I hope one you guys can help me. By the way, I am driving Pin1 (Enable) using PWM and other two inputs as just digital logic on and off.

Thanks.

Just a wild guess and please don't take offense but since the L298D is somewhat symetrical except for the Vcc1 and Vcc2 pins maybe the chip is backwards and those pins are switched.

Hi , I am 100% sure the IC is in correct orientation. I have checked it many times. all my resistors are 10K and I have 2X 100nF capacitors and one 100uF electrolytic capacitor in place, when I breadboard the circuit using just the IC everything works well,and motor doesn't run without its power supply. I am still scratching my head, but no clue.

when I breadboard the circuit using just the IC everything works well,

So you have answered your own question. The circuit design is fine, you have just wired it up wrong.

Have you tried measuring the voltages directly on the pins of the IC? Is the IC plugged into a socket - and if so is it fully in?

I think that chip will source all its power from VCC1 if VCC2 is disconnected or below the Vcc1 voltage, I seem to recall someone else having a similar problem.

It is always wise to test continuity in a circuit before applying power.

It is always wise to test continuity in a circuit before applying power.

Or apply the sniff test after applying power.

Sniff. Sniff. What's that smell? Where's that smoke coming from?

Except when its an LED burning, they give off poisonous fumes containing arsenic.

Except when its an LED burning, they give off poisonous fumes containing arsenic.

Well, there is that downside.

I have an L293D hooked up and the motor will not run if Vcc2 is not connected. It does run if Vcc2 is less than Vcc1.

If just Vcc2 is hooked up still no rotation.

You did have a common ground between them?

For now I would just bypass the regulator setup and just use the 5volt from the board.

So you have answered your own question. The circuit design is fine, you have just wired it up wrong.

Well, I did make a PCB for this (stupid me :frowning: ).

Have you tried measuring the voltages directly on the pins of the IC?

Not yet, but I'll do that continuity test and sniff test first :slight_smile: anyway I'll do it tonight.

For now I would just bypass the regulator setup and just use the 5volt from the board.

I did that, but the same result, I power the logic input from Arduino 5V and I didn't do that for long time, because I was afraid it will kill my Arduino board.

Thanks again for all the help.

So a PCB layout and maybe a photo of what you have would help us to see what is wrong.

So a PCB layout and maybe a photo of what you have would help us to see what is wrong.

Here it is.

And the photo to see how you built up the PCB?

I think the reason the 7805 is getting hot right away is that it maybe mounted backwards .

See if you are indeed getting 5 volts out of it.

If so you can unsolder it and flip it if it is a commom 7805.

Well its the right way round on the PCB graphic.... A photo would be helpful.

But where are the free-wheeling diodes? The L293 datasheet says external clamp diodes are required for inductive loads...

The L293D has inbuilt diodes. I'm still trying to figure out how he got the motor to work with just the logic hooked up but if the logic supply was also supplying the motor then that and the voltage drop thru the regulator would make it a little toasty. I like to put weak pulldowns on the enables and also run a ground wire (like a servo) with the wires for the control signals so as to form the common ground.

About the only reason to have the 7805 would be to use the motor voltage for the logic without having to supply another voltage that needs to be regulated. The arduino should easily supply the +5 for the L293D.

The L293 datasheet says external clamp diodes are required for inductive loads...

Datasheet states that it has internal clamp diodes.

I have tested the voltage levels on the pins today and I seems to me there is something wrong with the regulator. Because for a 5V regulator its output is about 6.11V without any loads. I have to replace it with a new one and I will let you know about the progress,


update: I just did a voltage test on IC pins and found out that VCC2 has 2.8V across its terminals with 5V logic supply signal inputs connected to the board. I am clueless... :roll_eyes:

The L293D is plugged in backwards. Look at the notch orientation on the board file (to the right) and look at it on your board (to the left).

justone:
The L293D has inbuilt diodes. I'm still trying to figure out how he got the motor to work with just the logic hooked up but if the logic supply was also supplying the motor then that and the voltage drop thru the regulator would make it a little toasty. I like to put weak pulldowns on the enables and also run a ground wire (like a servo) with the wires for the control signals so as to form the common ground.

About the only reason to have the 7805 would be to use the motor voltage for the logic without having to supply another voltage that needs to be regulated. The arduino should easily supply the +5 for the L293D.

Ah, I think I was looking at a datasheet for both the L293 and the L293D - its text wasn't careful to explain the difference!

The L293D is plugged in backwards. Look at the notch orientation on the board file (to the right) and look at it on your board (to the left).

How can be so blind :blush:, I would like to apologize from all the forum members who has contributed to this topic. I think I finally know what happened. I did the layout for this board and gave it to one of my good friends to develop it, he said he has altered the design a bit and I really thought that the IC was is in its original position. Well, really sorry guys, and thank you all for your valuable contribution. :slight_smile: