Control 12VDC motors (H bridge plans)

glaso

Hello:

I need to control two 80RPM 12 VDC motors. My budget is reduced so I want to use things that I have to control it. Now I have a Pololu dual motor controller which drive 1A per motor at 12VDC. I was thinking about using this controller as a PWM driver to drive a H-Bridge (if I can build it is better).

Does anyone have some good plans of an H-bridge to drive about 3A or maybe more?

Is it possible to do what I'm thinking?

THANKS!!

Jon Williams

Have you tried Google? I'll bet a quick web search will turn up all sorts of good ideas for your project.

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Jon Williams
Applications Engineer, Parallax
Dallas Office

glaso

Yes I tried and a found some plans but I need to know if the configuration proposed (with the Pololu microcontroller a the source of PWM pulses) is correct and if any H Bridge will be usefull for that.

Jon Williams

The Pololu has its own (low current) H-Bridge build on the board, so I don't think you're going to have much luck connecting it to an external circuit.

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Jon Williams
Applications Engineer, Parallax
Dallas Office

glaso

I was thinking on using the outputs of the Pololu Motor Controller to drive the H-Bridge as if they where the outputs of the stamp.
I don't know much how to do that but I think it can be done with some kind of H-Bridge design.

Dave Paton

Which Pololu controller are you using? From what I can see, they both revolve around the 754410 which is connected in a hard-H-bridge design. If you have the DIP version, you may be able to reverse-engineer the pinouts and set up your own output stage in place of the '4410, but it'lll be iffy. Is the only reason you want to do it is the serial interface and PWM? You can acomplish the same thing with a 74HC595 and a pair of LMD18245s I think, and not only would you get the benefits of PWM, but you get a much more capable and durable motor driver.

-dave

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glaso

Yes, I want to use the Pololu motor controller as a serial interface and PWM source, but if it is another way to acomplish that it will be great. How can I do this with the 74HC595 and the LMD18245 ????

Thanks!!!

Dave Paton

glaso said...
Yes, I want to use the Pololu motor controller as a serial interface and PWM source, but if it is another way to acomplish that it will be great. How can I do this with the 74HC595 and the LMD18245 ????

Thanks!!!

The '595 is an 8 bit·serial to parallel shift register with a cascade output so multiple chips can be put in series for looooooooong shift register construction. The '245s use·6 control bits to set direction, braking, and a 4 bit PWM speed. If you use 2 '565s in series (for a 16 bit shift register) and used one '245 on each, you could shiftout() your two 8 bit control byts in series with only 2 pins (a clock and a data). The apropriate datasheets are here:

http://cache.national.com/ds/LM/LMD18245.pdf

http://www.fairchildsemi.com/ds/MM/MM74HC595.pdf

There are a couple of good app notes on the 595 floating around the Parallax download site as I recall (anyone remember the AN# or the N&V column?), and the datasheet for the '245 is quite good at explaning things like the current sensing and the PWM. They also have some very useful notes on microstepping a bipolar motor with a pair of '295s in half-, quarter- and eighth-step modes using the PWM stuff. Very slick.

-dave

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Rick Brooks

I have used the Pololu dual motor controller to drive MOSFET H-bridges. Go to:

http://mysite.verizon.net/res0z5qw/Brooksbots

and click on the link to "Excuse II" for schematics. Just make sure that you add the 10K pull down resistors to the leads from the PIC to the SN754410. If you don't, when the reset is held low for any length of time, the output from the SN754410 tends to wander high which turns on all of the bridge legs (this is a bad thing!).

Choose the MOSFETs that deliver the current necessary.

Rick

David M. H.

I am new here but could not help noticing your posting about your motor drive woes. I am experimenting with H-bridges to drive small motors. My source of information is a book called Building Robot Drive Trains. In the book the authors describe several H-Bridges from a simple 4 transistor design using complementary pairs and a 74LS06 OC buffer as a direction·enable up to some single chip high current drivers such as a UNC2998 or a··UNC3951 which can drive 2 motors at 2 amps with a 3 amp peak.

I·bought my copy on-line at the Servo magazine bookstore. The book also talks about using these H-bridges and drivers with your BASIC Stamp and other processors.