H-bridge with Pic

i don't know what you're using for an H-bridge? but if it's a FET type, you most likely are having high side problems. you need to use P and N channel so that you make sure the source is ways directly to a rail. they do make high side fets just for driving motors how ever, there is a boot strap cap in them and your suppose to pulse the signal do that the cap can discharge and be ready for the next pulse. this means you must perform PWM with in the rated spec's for the transistors..

if your doing bipolar outputs, then you must have a sequence problem? P.S. some Pics have flags to force pull up on the outputs, maybe your not enabling this ? if you have a scope, you should be able to see this happening?

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Here is a data sheet for the L293

Does the sample circuit on it that looks like your use of the chip?

yes i am using this one, actually the L293D.

turn ever slowly. Would I burn anything if I hook up dc voltage directly to it? basically there are three input for each motor. I guided myself with tis tutorial

on page 7 and 8

k

I would start by eliminating any possibility that the PIC is involved in the problem, by just jumpering the 3 inputs to either +5 or ground, to check out the bridge driver. Don't forget to include a bypass capacitor between the 12 volt and power ground pins of the 293. You can use a 1k resistor in place of the motor for the first test. You should be able to check out both halves of the bridge with a volt meter.

well I hooked up pin 16,15 and 10, Pin enable 2 was left out and indicated Vcc, enable 2 did not affect the output even conencted with Vcc On the side i connected Pin 2, 7,8 , this time voltage indicated zero until I put enable pin1 to Vcc. Enable pin is not working right ? k

I am trying to getthe same result bu the chip is not giving anything now, Yes it is Dip what i did before was 16,15 and 10, = 12v Pin 12, 13 = GND

On the side i connected Pin 2, 7,8 , = 12v Pin 4,5 = GND

Ken

I am leaving, wont be back til mid week

Okay, the data sheet for the L293D is:

I assume you are using the 16 pin DIP package. So ground goes on some selection of pins 4,5,12,13 (these pins also function as the chip heat sink). The +12 volt motor supply connects to pin 8. The +5 volt logic supply connects to pin 16. Assuming the inputs are TTL type circuits, an open input should act like a logic high signal, but the input 1 and 2 do not have the asymmetrical currents of TTL inputs, so this may not be a safe assumption. I would tie inputs to +5 as a high input.

I am not sure I am interpreting your test results correctly.

Try connecting a pair of 1k (or something similar) resistors in series across the 12 volt supply, and the center node to one output at a time. This will produce about 6 volts if neither driver is on (when the enable is low), about 11 volts if the pull up driver is on (enable and the input for that side high), and about 1 volt is the pull down driver is on (enable high and the input for that side low).

Then connect the divider to the other output and test it.

Can you supply a circuit for me to look at?

lerameur wrote:

HI, I have free internet acces at this hotel. I think i found the problem I was actually putting 12v on both side of the motor, hats why I was not reading anything. I will just need to remove the link to one of the pin. I will try that when i get back home

Also, I think I know the answer but I would like to confirm this with you guys. I am using this dc gear motor,

the one I am looking for is the 12v geared at 1/624

this uses a lot of amp, will it work with the L293D ? (I dont think so). but,then the graphic is hard to read thanks

k

Wrighty wrote:

I think you will hardly be able to run this motor above zero torque (900 mA at zero load). At peak efficiency point (about 65%, around 800 g-cm motor torque) the drive current requirement is about 6 amperes.

If you used the 24 volt motor (with 12 volt drive for something like a quarter of the output power) you would hit the best efficiency point at about 1.6 amps, but you are paying for 4 times the motor you are using.

but my biggest worry is the L293 H-bridge, it can handle only 1.2 amp continuously. its either not going to supply the motor with enough current or heat up with too much current that the motor needs. K

I am agreeing with you.