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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

Adjit
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  • Please clarify what kind of switches you use. Are they self-returning or returned with a repeated press? – motoprogger Apr 20 '14 at 02:11
  • @motoprogger I was thinking of using an SPDT lever microswitch – Adjit Apr 20 '14 at 02:16
  • 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? – motoprogger Apr 20 '14 at 02:22
  • @motoprogger Honestly, not sure. This is the microswitch I was looking at https://www.servocity.com/html/spdt_miniature_snap-action_mic.html#.U1MtkvldWSo – Adjit Apr 20 '14 at 02:28

8 Answers8

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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

Spehro Pefhany
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  • 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? – Adjit Apr 20 '14 at 13:58
  • 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. – Spehro Pefhany Apr 20 '14 at 14:10
  • so this switch (https://www.servocity.com/html/dpdt_20-amp_momentary_flip_swi.html#.U1PWLvldWSo) would not be usable, I would have to get a relay, correct? – Adjit Apr 20 '14 at 14:14
  • Right, something like this (this is a 12V type) would probably suit, but it depends on your motor: http://www.jameco.com/1/1/26785-k10p-11d15-12-general-purpose-blade-octal-relay.html – Spehro Pefhany Apr 20 '14 at 14:31
  • 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? – Adjit Apr 20 '14 at 14:43
  • Current rating should meet or exceed the stall current of the motor (LRA) and coil voltage the same as the motor for convenience. DPDT. Make sure the coil is a DC type. When you've picked out a motor and tentative relay you can ask another question and someone will help. – Spehro Pefhany Apr 20 '14 at 14:48
  • Can you please update the answer with the required electrical components? – Adjit Apr 20 '14 at 15:19
  • Last question, I promise... I have built this circuit with an arduino, I had a potentiometer controlling speed and a switch reversing direction of the motor and on/off switch. Do you think it might be easier to do it with the arduino? or is it better to do it using circuit logic? – Adjit Apr 20 '14 at 15:39
  • Easier with the Arduino, for sure, but hardware limit switches are more sure. – Spehro Pefhany Apr 20 '14 at 15:43
  • Right, I was thinking of using the switches in conjunction with the arduino – Adjit Apr 20 '14 at 19:19
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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

Joe
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I know this post is 6 year old but, I hope this helps you in some way or at very least helps others who see it and need it?

The circuit is actually very simple but hard to explain. Using a 3PDT (Triple Pole Double Throw) relay,

  • Wire the first two poles as if it were a DPDT reversing relay.
  • Connect Positive Power to the relay coil.
  • The negative of the coil goes to the N.O. (Normally Open) of first LS (Limit Switch).
  • The negative of the coil also goes to the COM (Common) of the 3PDT's third pole.
  • Connect Negative Power to both the COMs of the LSs.
  • Connect N.C. (Normally Closed) of the second LS to the N.O. of the 3PDT's third pole.

enter image description here

This can also be done with a DPDT and a SPDT relay.

enter image description here

Adding this per @Transistor . I hope it works. Circuitlab wants me to pay to use and save. So I don't use it.I also don't use it because It has very limited parts as in no triple pole double throw relays. But since I added the DPDT and SPDT option I thought why not. So here it is.

schematic

simulate this circuit – Schematic created using CircuitLab

Mouthpear
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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.

gbarry
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  • so how would that work adding in an on/off switch? – Adjit Apr 20 '14 at 02:42
  • 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. – gbarry Apr 20 '14 at 04:10
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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.

sparky Al
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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.

Rikil Shah
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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.

John A. Richardson
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I am going to add this one because someone mentioned bistable relays. If anyone wants to make it really easy on themselves for just a few more dollars, you can use this module. The relay is self latching and only needs a negative trigger.

  • V+ Connect positive voltage
  • S1 Set1 is your negative voltage from Limit Switch 1
  • R1 Reset1 is your negative voltage from Limit Switch 2
  • SX SetX positive voltage
  • SY SetY negative voltage
  • RX ResetX negative voltage
  • RY ResetY positive voltage
  • CX CommonX Wire to motor
  • CY CommonY Wire to motor
  • The commons on the Limit Switches go to negative
  • You may have to reverse the motor so do it before you put in place, to avoid platform collision. The switch will not reverse the motor if the set and reset are going to the wrong switches. Damage will occur.

enter image description here

Mouthpear
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  • Welcome to EE.SE. We prefer schematics over wiring diagrams as they show the *schema* of the circuit. You can add one in using the CircuitLab button on the editor toolbar. Double-click a component to edit its properties. 'R' = rotate, 'H' = horizontal flip. 'V' = vertical flip. Note that when you use the CircuitLab button on the editor toolbar and "Save and Insert" on the editor an editable schematic is saved in your post. That makes it easy for us to copy and edit in our answers. You don't need a CircuitLab account, no screengrabs, no image uploads, no background grid. – Transistor Jul 19 '20 at 20:03
  • @Transistor I added one to my first answer. It doesn't do much good to make one for this answer since that site does not have this relay and I am not spending time to try and figure out how to make one, or even if the site will let me keep it since it's NOT free to be a member. I don't find it worthwhile to have to keep making the parts over and over and you can't even save any of it. Not to mention how often it crashes and it only lets you make small circuits. You get too big and it wants a paid membership. Are my wiring diagrams not good enough to follow? – Mouthpear Jul 19 '20 at 22:09
  • The wiring diagrams are clear if wiring is what you are trying to show. For good clear understanding of how a circuit works a well laid out schematic is best and what professionals use. – Transistor Jul 19 '20 at 22:13
  • @Transistor well in this case yes, it's all just wiring. It's all just components that need to be wired together. I add the schematic for the bistable relay module just for reference but even that is just 2 diodes and a relay. I can do my professional in my Autodesk Suit but I use that for more complex circuits. But most people can't follow the pin lines and mapping. So I keep it simple, when showing these easy peasy wiring diagrams. I am not trying to insult the OP but judging by the diagram they provided, I was assuming they'd prefer a practical wiring version.I did make 1 for you to look at – Mouthpear Jul 19 '20 at 22:35
  • @Transistor Was either one of my answers suitable? Or a good answer for an up vote?? – Mouthpear Jul 19 '20 at 22:37