Author Topic: Help with H bridge!  (Read 3536 times)

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Offline Half ShellTopic starter

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Help with H bridge!
« on: November 09, 2007, 07:46:35 PM »
I am having a nightmare with this damned circuit.

I am using a Texas Instruments SN7544 0NE (thats a zero, not an o) integrated circuit. It has two h bridges.

Here is the spec sheet:
http://focus.ti.com/lit/ds/symlink/sn754410.pdf

Here is a tutorial using the same chip and the microcontroller I am using:
http://itp.nyu.edu/physcomp/Labs/DCMotorControl

I have checked 30 times, everything is wired correctly. I have the chip properly grounded across the bread board. Here's the problem -

Whenever I turn on the microcontroller and tell the h bridge to go, I hear the motors whining ever so slightly - they are running on a 9 volt battery as opposed to my controller's 5 volt power supply (from the computer right now). I remove the negative lead of the motor and place it directly into ground, leaving the positive lead in the h bridge circuit. Sure enough the motor runs, at the speed I wanted it to as well! I even tested it - changing the PWM value when doing this does indeed change the speed of the motor.

This would be great IF I wanted to run the motor in one direction. Telling the H bridge to reverse directions this fails miserably as I have to plug the negative lead in and put the positive lead to ground!

Why is it when I have the chip wired correctly it is whining ever so slightly and refusing to move?

Any help would be GREATLY appreciated. This problem is holding back two projects and maybe soon to be three!

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Re: Help with H bridge!
« Reply #1 on: November 09, 2007, 07:59:20 PM »
Hmmmm I suspect that the circuit isn't doing what you think it is doing . . . use a multimeter and check the pin voltages to see if they are correct. This way you can narrow the problem down to a specific pin.

Quote
I hear the motors whining ever so slightly - they are running on a 9 volt battery
Im not sure what motors you are using, but 9V batteries can't supply very much current. You should get some better batteries :P

Some battery tutorials that might help you:
http://www.societyofrobots.com/batteries.shtml
http://www.societyofrobots.com/battery_calculator.shtml

Places to buy batteries:
http://www.societyofrobots.com/robot_parts_list_battery.shtml

Offline Half ShellTopic starter

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Re: Help with H bridge!
« Reply #2 on: November 09, 2007, 10:48:07 PM »
They're 9 volt motors - I'm trying to build smaller robots that navigate the home and allows me to easily play with new stuff I don't know about like mapping.

I got it to work - I had to ground the 5 Volts going into VCC2 as well into the microcontroller. That was what the problem was.

Thanks for the help!

Quick question though - if I use one voltage regulator and force 5 volts to those 9 volt motors there isn't really any downside is there?

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Re: Help with H bridge!
« Reply #3 on: November 09, 2007, 11:09:37 PM »
Quote
Quick question though - if I use one voltage regulator and force 5 volts to those 9 volt motors there isn't really any downside is there?
There is quite a few but Im too lazy to list them . . . don't regulate the voltage going to a motor, bad stuff will happen. ;D

Offline Half ShellTopic starter

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Re: Help with H bridge!
« Reply #4 on: November 09, 2007, 11:27:58 PM »
Thanks for the warning. I am keeping motors with their own power supply right now and am using the regulator for the sensors in the circuit. I also decided to just run the 9 volts at 9 volts and will just have to invest in a 9 volt rechargeable so I don't have to use 6 AA's to run the damned thing.

 


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