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View Full Version : 15amp 24V H-Bridge and Pulse width Modulation



Steven
03-02-2005, 01:25 AM
I would like to know if anyone has ever built a H-Bridge that can handle 24V at 15Amps, and then how they contorlled it with the Basic Stamp 2 module? We are converting a 24vDC wheelchair into a robot, and have come into some severe problems. We want·to build the H-Bridge instread of buying it. We were using this h-Bridge:

http://www.bobblick.com/techref/projects/hbridge/hbridge.html

·This is not working correctly for us. If anyone has any good ideas please let me know.

Thanks
Steven

SPENCE
03-02-2005, 02:27 AM
Suggest you contact bob blick and ask hiom if he has deign for a higher current version of the reference item?

73
spence
k4kep

Steven
03-02-2005, 02:55 AM
·I know that the circuit he has built handles the current, but my issue is that I do not know how touse the basic stamp to properly send out the PWM without using his Servo Pulse to PWM circuit. I was hoping that Someone would be able to direct me in the right way to the correct code for the PWM using the Basic Stamp.

Bean
03-02-2005, 03:04 AM
Note that the Basic Stamp version of PWM is geared towards D/A, and not for an H-bridge.

The Stamp PWM is really I guess pulse density modulation.

You want a true PWM signal for an H-bridge.

Bean.

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Check out· the "SX-Video Display Module"

www.sxvm.com (http://www.sxvm.com)
·

SPENCE
03-02-2005, 03:07 AM
CHECK THIS PAGE. MAYBE IT WILL HELP.

http://www.bobblick.com/techref/projects/sv2pwm/sv2pwm.html

I HAVE NOT GOTTEN THAT FAR YET BUT AM HEADING SOMEWHAT PARALLEL WITH YOU. BOUGHT A 7 CHAN FUTABA 75 MHZ FOR MY WIFE TO USE WITH
A MOBILE ROBOTIC BASE. CARRYING A CAMERA AND OTHER STUFF.
SHE CAN RUN IT OUT ON THE DRIVE TO VIEW THE RFD MAILBOX.. SHE IS WHEELCHAIR BOUND. NOW IF I COULD JUST TURN IT INTO A GARDENERS HANDYMAN SHE WOULD BE REAL PLEASED.

73
SPENCE
K4KEP

Tom Walker
03-02-2005, 03:17 AM
In the simplest configuration, your Stamp would use the PULSEOUT command to send pulses to either your "IN A" or "IN B" input. Bob actually mentions this on the page describing his design. (remember, in a typical H-bridge, if you have both A and B high at the same time, you let let some magic smoke out and can even start a pretty fire...Bob's design tries to prevent this from happening, but just in case you try another design...). The Stamp's PWM command is not generally used for this because it does not generate a "regular" PWM signal...it was not really designed for that (this topic is covered elsewhere), but Parallax does make the PWM-PAL for just this purpose.

This looks fairly straightforward but it sounds like some more independent study <g> might be in order.

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XYZZY...PLUGH...*poof*

Rick Brooks
03-02-2005, 09:02 AM
I've built FET H bridges based on the Pololu Dual Serial Motor controller that can handle up to 18 amps continuous at 35 volts. These are good for smaller motors, but would not hold up to a wheelchair motor.

I'd suggest one of the products from http://www.roboteq.com/. I've bought two so far and am using them in a 75 pound and a 150 pound sumo robot. They are easily driven directly from a Stamp (serial out command).

Rick

Beau Schwabe (Parallax)
03-06-2005, 02:15 PM
Bean said...

Note that the Basic Stamp version of PWM is geared towards D/A, and not for an H-bridge.

The Stamp PWM is really I guess pulse density modulation.

You want a true PWM signal for an H-bridge.



Did you say PDM "pulse density modulation"?

here is a solution that I have used in the past, that will convert PDM or straight analog
input into a PWM signal that is a little bit more "motor friendly".


Note: (for reference we will use (PWM) signals from the stamp and PWM for the output of this circuit)
1) The active input range is between 2.2V to 3.7V anything outside of this range will clip to 0% or
100% PWM duty cycle on the output.

2) Using the BS2 (PWM) command, the approximate active range is between 112 and 188 for (PWM) values.

3) With regular (PWM) updates from the Stamp, this circuit will HOLD the output PWM value for several
seconds while other programming tasks within the Stamp can take place.

4) With the component values used, the base PWM frequency runs at about 6kHz.


Forgive the blurry pictures.... I can't quite seem to get the hang of it with the proper distance my camera
should be.

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------------------------------------------------------------------------------------
Beau Schwabe - Mask Designer III

National Semiconductor Corporation (http://www.national.com/)
(Communication Interface Division)
500 Pinnacle Court, Suite 525
Mail Stop GA1
Norcross,GA 30071
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Post Edited (Beau Schwabe) : 3/6/2005 7:22:34 AM GMT