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Author Topic: L293D Motor driver issue - please help!!  (Read 2798 times)
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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.

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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.

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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.
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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.
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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.
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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?
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Except when its an LED burning, they give off poisonous fumes containing arsenic.
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Except when its an LED burning, they give off poisonous fumes containing arsenic.
Well, there is that downside.
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 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.
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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 smiley-sad ).

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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 smiley anyway I'll do it tonight.

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

Here it is.

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And the photo to see how you built up the PCB?
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 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.
« Last Edit: October 16, 2011, 11:42:39 am by justone » Logged

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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...
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