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I'm making a circuit that I used for a previous project on a bread board to power two electromagnets. I'm using the same wiring and parts as the first time. It's a simple circuit using an Arduino to control a motor bridge.

Here's the problem: when I try to operate it from the arduino, nothing happens. When I run the logic pin (and Vref, etc) through the 12v power supply I would use for the electromagnets (instead of the arduino), everything works fine.

Using an voltmeter, the arduino looks fine with volts going up to (and a little over) 5v. The motor bridge is 4.5~20v. Instead of a magnet, I'm just using a voltmeter for testing. The ground is run through the power supply, not the Arduino

Here's the circuit: circuit http://www.e-alexander.net/slippers_img/circuit1.gif and the schematics for the ta7291P http://www.electronicaestudio.com/docs/1437_2_4025.pdf

I have multiple ta7291P motor bridges and all have the same problem: all worked fine last year when I did the project, but now none of the work from the arduino, none of them work from a 5v constant current used instead of the arduino (second input pin is grounded in that case), all of them work with 12v used to power everything.

Are my chips just aged/abused or am I missing something?

Thanks in advance!

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    \$\begingroup\$ Do you have a common ground between the 12V power supply and the Arduino? \$\endgroup\$ – PeterJ Dec 13 '13 at 4:54
  • \$\begingroup\$ Yes, to the 12v power supply. Arduino is powered through USB. \$\endgroup\$ – Norbles Dec 13 '13 at 5:41
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    \$\begingroup\$ Is the negative terminal of the 12 volt power supply connected to the Arduino ground? \$\endgroup\$ – Peter Bennett Dec 13 '13 at 8:09
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am I missing something?

As others have commented, you are missing the common ground connection.

enter image description here

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  • \$\begingroup\$ Yes, that fixed it. Now I'm only confused with how I had a 6 motor bridge set up running perfectly with this configuration for three months with out ever connecting to the arduino ground pin. I have photos of my old set up that I double-checked. I never connected the arduino gnd because I was afraid of shorting through it. \$\endgroup\$ – Norbles Dec 13 '13 at 12:32

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