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I am doing a project on a door shutter opener where there are two states or signal I pass into the circuit:

  • 0V: Door shutter closed

  • 5V: Door shutter opens.

I plan to accomplish this via motor control. The problem is I need to reverse the polarity of motor to change direction so this basically works like a DPDT switch except that I have to do this via electrical signal.

How do I accomplish this and is it possible to do this via transistors or gates?

I've done basic electrical science course in college till now so I would appreciate it if you can talk at my level of learning.

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    \$\begingroup\$ Dave Tweed's answer is nice and simple (which goes a long way in real-life applications), another way to reverse a DC motor is to use an H-bridge circuit, there are plenty of motor-driver chips out there which are a complete H-bridge, or you can build your own. \$\endgroup\$ – John U Feb 19 '13 at 14:56
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    \$\begingroup\$ I concur the H-bridge circuit would be my choice, the DPDT relay is a simple and quick solution but since your talking about a door opener I would be concern with number of cycles on the chosen relay but that's a function of the traffic through the door \$\endgroup\$ – Kvegaoro Feb 19 '13 at 15:32
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The most direct way to implement this would be to use a DPDT relay to reverse the power to the motor, along with a limit switch at each end of the door travel to cut the power when the door reaches the desired position.

schematic diagram

The two limit switches are labeled "closed" and "open". Terminal "A" on the motor is positive relative to "B" to drive the door to the closed position, and vice-versa to drive it open. When the door is fully closed, the normally-closed switch labeled "closed" opens. Similarly, when the door is fully open, the switch labeled "open" opens.

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  • \$\begingroup\$ Can you give me more info regarding the limit switch? \$\endgroup\$ – Prabhpreet Feb 20 '13 at 10:27
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    \$\begingroup\$ Beware relays that "make before break". Some relays are designed that way, some are designed to "break before make", some are not specified either way. If you try to reverse the polarity of a live circuit with make-before-break contacts, you will briefly short out the power, and that could damage or weld the contacts. \$\endgroup\$ – Solomon Slow Nov 9 '15 at 18:34
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The switches can be wired in series and a reverse connected rectifier diode can be wired across each switch to enable each direction, save one conductor. Al.

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    \$\begingroup\$ Can you edit a schematic into your post to make the circuit a bit more clear? (There's a schematic editor built into the site.) \$\endgroup\$ – Greg d'Eon Nov 9 '15 at 19:20
  • \$\begingroup\$ How do you upload a file and what format? I have it in DXF or PDF. All you do is take two conductors out to the motor with the two switches and motor all in series, across each SW place a rectifier, each reverse biased to the other. \$\endgroup\$ – Alan Inness Nov 10 '15 at 20:59
  • \$\begingroup\$ If you try editing your post, there's a schematic editing button in the top toolbar. \$\endgroup\$ – Greg d'Eon Nov 10 '15 at 21:10

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