Pin and controls of hbridge (h293d)

[anilg]

I'm buling a car and using a hbridge IC to control the car. The IC pins are as follows

http://www.tigoe.net/pcomp/img/stepper-bipolar-hbridge.jpg

A couple of questions about this IC..

*What is the enable pin(top left)  for? The motor runs fine with or without this connected.

*Also I understand that sending the following signals does the following

00 = nothing (break)
01 = clockwise rotation
10 = anticlockwise

What is 11 for? I understand it is also used to break, but is it recommended over 00.. Also I recollect reading that a 11 connection can harm the IC.. is this true?

[Maltaeron]

Don't really understand it all myself, but this is admin's tutorial on h-bridges:

http://www.societyofrobots.com/schematics_h-bridgedes.shtml

I guess 1 1 is "break" too, then,  (Muffled laughter)

[robonoob]

well thats what admin says in his tutorial

A=1 B=1 : Your circuit explodes into pretty sparks

[Ro-Bot-X]

Enable pin connects or disconnects the motor to the H-bridge. When connected, the motor will spin clockwise or counterclockwise or will be braked. When disconnected, the motor can freely spin. Also the Enable pin may be used for PWM.

00 or 11 connects both ends of a coil to the same potential, eighter GND or Vcc. It does not matter which one of them are you using, they both do the same thing: shorting the coil. So, when the motor is spinning and you short the coils, the motor becames a generator and the voltage generated will go back to the motor and tend to generate a rotation in the motor but in the opposite way the motor is spinning, thus rapidly slowing it down. Never used this for steppers. To slow down a stepper, just give it steps at a slower rate until it stops. Then, if you keep the coils energised (01 or 10), the stepper will hold it's position. Depending on the force needed to hold that position, you can short both coils, energise one coil and short the other, or energize both coils.

[gmatkins]

I've heard inputs of 11 and 00 referred to as "braking high" and "braking low" respectively. Like the last poster said they both connect the two terminals of the motor together and in doing so use induced current to slow the motor. Neither one will harm the H-bridge, but since H-bridges are implemented using both P and N type transistors, one or the other tends to bleed a little bit more current. Buggered if I can remember which is which though.

[anilg]

Thanks for the detailed reply..

Enable pin connects or disconnects the motor to the H-bridge. When connected, the motor will spin clockwise or counterclockwise or will be braked. When disconnected, the motor can freely spin. Also the Enable pin may be used for PWM.

Hmm.. I still dont get it.. I was able to rotate the motor both ways with or without enable connected.. As far was working with the motor it behaved exactly the same whether enable was connected or not.

00 or 11 connects both ends of a coil to the same potential, eighter GND or Vcc. It does not matter which one of them are you using, they both do the same thing: shorting the coil. So, when the motor is spinning and you short the coils, the motor becames a generator and the voltage generated will go back to the motor and tend to generate a rotation in the motor but in the opposite way the motor is spinning, thus rapidly slowing it down. Never used this for steppers. To slow down a stepper, just give it steps at a slower rate until it stops. Then, if you keep the coils energised (01 or 10), the stepper will hold it's position. Depending on the force needed to hold that position, you can short both coils, energise one coil and short the other, or energize both coils.

I'm using a geared DC motor and not a stepper .. but thanks for your explaination. How are these positions (00 and 11) different for a DC.

[Ro-Bot-X]

The picture you posted shows a stepper motor. So, I supposed you are using steppers.
The H-bridge can drive ONE stepper motor (2 coils) or TWO DC motors (one coil each).
00 and 11 do the same thing: short the coil (connects the 2 leads of the coil together). It does not matter which one you use to slow down your motor.

Motors come in different qualities. A good quality motor is also a good generator. Try this: connect your motors in paralel and spin one motor (no batteries) with your hand. If the other motor spins at the same speed, the motors are high quality. Now short the leads and spin it again. It should be a lot harder to spin. This is the bracking effect. Connect the motor to the batteries and let it spin a while, then quickly take one lead and put it over the other lead (short the leads). You will see the motor quickly slowing down to stop. Connect it back to the batteries and after a while just disconnect one lead. Now the motor will continue spinning, slowly slowing down to stop. If the motor does not behave like I just described here, it is a low quality (and efficiency) motor, don't use it.

About the Enable pin. Try this: have the Enable connected to positive (5V), and connect the 2 input pins together (short them). Spin the motor by hand. Try to see how hard it is to spin. Now disconnect the Enable from positive and connect it to ground. Leave the input pins shorted. Spin the motor. It should be a lot easier to spin. If it doesn't behave like this, you have something wrong there.

[anilg]

thanks for that great reply. Answered my questions perfectly...

Usually one gets the physics of what is doing, but watching one motor power the other was very cool A great prop for some hands on talk on magnetism

[Admin]

The reason for the enable pin setup, instead of what you see in my H-bridge tutorial, is that it is much easier for a programmer to control a motor driver without having to bother learning/understanding how an H-bridge actually works. It also prevents the pretty sparks command