Let's Make Robots!

More L293 Problems-Any Ideas?

Here's the idea-to use the L293 as a one direction speed control with PWM on the enable.  Theoretically I could do something like this:

With a pull-up and a pull-down to the logic pins respectively to keep one high and one low.  The problem is when I tried it, this happened:

The motor never moved and the chip and the board are one now, I'm afraid.  Luckilly I bought about 8 of these.

I tried a more conventional circuit with digitalWrites high and low on pins 2 and 7 and it's getting hot again, so I'm beginning to wonder if I have a slew of bad chips or if it's more of a misunderstanding of the chip itself.

So the question is, is my logic incorrect or is there another problem here?

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...and why did it get so much hotter at the "south" end of the chip?

That could be as simple as the fact that the more melted end was smaller, closer the end, while the other direction still has the internal metal strips and a bigger mass of plastic to help conduct away some of the heat. I am still looking at the major heat being in the middle of the chip, which is not just the grounds, but the actual location of the chip itself inside. The wire traces spread out to the various pins from there.

The ground pins in the middle of the chip are intentionally made heavier (inside the chip) to help conduct away heat, so the more severe melting around the ground pins, just says to me the integrated circuit inside probably got quite hot, -so hot it started to melt things.

I gotta say, there are very few things one could do to cause this and I would be surprised if Max would have done any of them. I mean, he (you) went as far as to do the pulling up and down of the dir pins with resistors. The schematic is as simple as it gets, the breadboarding is as simple as it gets and we are using the "standard" PWM from the Arduino (no screwing around with timers and PWM freqs). Beyond that, I could not imagine a super-huge motor being plugged into this.

If I were putting down money, I would say that we are looking at a plain-ol' bad chip or some kinda litte-bit-of-metal or something that is bridging some strips on the breadboard.

Thanks for posting this ..... looks like the toast burnt the breadboard ;-)

What i don't understand is these chips have a "Thermal Shutdown" circuit....... i have on many occasion invoked this part of the circuit ........ it gives a stop start effect......ie chip works, motors run, motor takes a tad too much current heats the chip up and the thermal shutdown circuitry trips and shuts power off to the motors......until it cools down enough and switches back on again....... Quite a useless mechanism actually.

Questions about your picture :-

  1. Did it vaporize the resistors too....
  2. Pin 1 of your chips are not in the same direction on the circuit board
  3. Did you use Lipos or recharge batteries
I'm thinking of making a piece of jewelry out of this breadboard. Here are the answers to your questions: 1. Nope-the resistors survived and went on to another breadboard. They were 1/4 W 10 K Ω carbon film. 2. The AT Tiny 45 in the photo never got hooked up. I was testing the motor side of the circuit with an Arduino UNO and had only seated that chip in anticipation of smooth runnings. The enable pin going to the Arduino was the one in the lower left corner of the chip as it appears in the photo. I cleared the wires for the shot half so you could see it and half in disbelief. 3. I used 4 AAA for the motor and USB line for the Arduino.

Wow, that's a lot of current to melt that from just triple-A batteries...  Actually, the chips being backwards to each other, (even though the one never got powered up,) does still make me wonder if the 6 volts for the motor got hooked up to where the +5 should have been. Not sure even that would have caused so much heating, though.

Next time put your finger on the chip and be ready to disconnect the power if it starts to get hot.

If your a techie then use a multi-meter to monitor the current.

LOL, good advise. I am using my fingers all the time...never trust a technical device ;-)

Quit showing off your mad Photoshop skillz. I know anyone can deform a whole image, but, you learned to distort only half the image while leaving the other half unmolested. :P

I wish I could fix the problem in Photoshop!