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So here is what I am trying to do... have a DC motor wired to an on/off switch and 2 microswitches. Each switch will reverse the direction of the motor, so one switch tells the motor to go forward, the other tells the motor to go reverse. My goal is to have a track where the motor will pull a platform in one direction, then when it gets to the end of the track it will hit the switch and then cause it to go the other way down the track. And I would also like to include an on/off switch for the whole circuit.

I am just curious to know what the best circuit for this will be.

My initial thought is to use a DPDT switch but not exactly sure how to get that working, or what the proper circuit layout is for it.

This is the schematic for my basic idea, but (correct me if I'm wrong) the motor will only go in the forward/reverse direction if the switch is continuously pressed.

enter image description here

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  • \$\begingroup\$ Please clarify what kind of switches you use. Are they self-returning or returned with a repeated press? \$\endgroup\$ – motoprogger Apr 20 '14 at 2:11
  • \$\begingroup\$ @motoprogger I was thinking of using an SPDT lever microswitch \$\endgroup\$ – Adjit Apr 20 '14 at 2:16
  • \$\begingroup\$ I didn't manage to find out anything about their behaviour, Do they toggle with each press or do they turn "on" only while pressed? \$\endgroup\$ – motoprogger Apr 20 '14 at 2:22
  • \$\begingroup\$ @motoprogger Honestly, not sure. This is the microswitch I was looking at servocity.com/html/… \$\endgroup\$ – Adjit Apr 20 '14 at 2:28
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You will need a memory element such as a relay to hold the current direction of the motor.

schematic

simulate this circuit – Schematic created using CircuitLab

Here a DPDT relay and two microswitches are used. The motor M1 drives to the "left" when the top terminal is positive and to the right when the top terminal is negative.

Suppose the relay is dropped out. The top terminal is positive, SW2 and SW3 are in the positions shown. When the motor reaches the left limit, SW2 is actuated, energizing the relay. The motor immediately reverses, but the top contact has pulled in, keeping the relay energized through D2. The motor operates until SW3 is actuated, which interrupts current to the relay (D3 catches the flyback voltage). The relay drops out, releasing the hold contact and it remains dropped out, and we're back where we started.

Interrupt V1 to switch everything off (and it will always drive to the left when power is applied). Interrupt only the current to M1 and the memory of the previous direction will be maintained as long as V1 is applied (which means continuous draw if the relay is energized).

A solid-state solution could use a single CMOS gate package (eg. 1/2 a CD4011B) and a MOSFET H-bridge to drive the motor:

schematic

simulate this circuit

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  • \$\begingroup\$ What would be the advantage of the solid-state solution? Is there a difference between a DPDT switch and a DPDT relay? because if I use a DPDT switch would you suggest a momentary switch or a non-momentary one? \$\endgroup\$ – Adjit Apr 20 '14 at 13:58
  • \$\begingroup\$ Not a lot of advantage to solid state in this case- no relay clacking or to wear out. Both switches are momentary. A relay is essentially a switch actuated by a coil. \$\endgroup\$ – Spehro Pefhany Apr 20 '14 at 14:10
  • \$\begingroup\$ so this switch (servocity.com/html/…) would not be usable, I would have to get a relay, correct? \$\endgroup\$ – Adjit Apr 20 '14 at 14:14
  • \$\begingroup\$ Right, something like this (this is a 12V type) would probably suit, but it depends on your motor: jameco.com/1/1/… \$\endgroup\$ – Spehro Pefhany Apr 20 '14 at 14:31
  • \$\begingroup\$ What is a good equation to use so that I can figure out what relay to get for my motor? as of now I don't know what motor I am getting. So the simplest way for me to control the power of the circuit would be to just use a SPST switch by V1? \$\endgroup\$ – Adjit Apr 20 '14 at 14:43
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Setup so each side can reverse the direction. DPDT switches on each side.

schematic

simulate this circuit – Schematic created using CircuitLab

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A DPDT switch is what you want, because if the two microswitches don't act together perfectly, you will have a short circuit and a fire. The DPDT layout is just like you have there. Imagine you glued the two switches together side by side. The DPDT is made just like that.

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  • \$\begingroup\$ so how would that work adding in an on/off switch? \$\endgroup\$ – Adjit Apr 20 '14 at 2:42
  • \$\begingroup\$ If you want reversing, and also a switch to turn the motor off, simply break the wire from the battery and add an additional SPST switch there. \$\endgroup\$ – gbarry Apr 20 '14 at 4:10
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reversing of a dc motor

This is a minimal reversing circuit. It doesn't start on it's own, you have to push a limit switch. It doesn't have interlocks or a stop button, but it can all be added to it. The interlocks are specially important, because if both relays are on, it would be a short circuit. The circuit uses 2 relays, 2 limit switches, and a dc motor. As illustrated, the relays have to be dc, same coil voltage as the motor, but the bottom can be separated and fed from a different voltage.

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This can be solved using Sphero's very ingenious circuit or as you said, using Arduino. In case, your motion doesn't have much parameters like speed regulation, occasional calibration or any other, Arduino might be overkill.

Middle ground can be reached using a Bi-stable multivibrator using timer IC viz 555. In this you can have certain parameter setting like sensitivity of input switches or debouncing. But again, all depends on hardware cost target of the specific project.

In of the similar project, I am going to use bare-bones DPDT relay circuit.

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use a dpdt switch with "center off", there are six terminals 1-6 1 and 2 connect to power, also run a jumper from 1 to 6 and another from 2 to 5 forming an "X". 3 and 4 is the connection to the motor so run a lead from those two to the motor...you need the center off type switch to prevent shorting out and blowing a fuse.A dpdt relay has no center off so one position will blow a fuse and the other will run the motor don't use a relay unless you design a special circuit with a delay or something to prevent shorting out. Sketch it out and you can see how simple it is. Mc master-Carr has that switch.

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protected by Community Feb 13 '17 at 21:33

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