I have been playing around with a circuit and I need some help. I have wracked my brain for a few hours moving around components and I just can't seem to figure it out.

I have spst switches and would like to use them to reverse direction of a low power motor. One for clockwise, one for counter clockwise.
I came across many options for spdt and dpdt switching, but can this be done with 2 spst and possibly a couple diodes? I know leds dont have much to offer for reverse polarity protection, but it would be nice to use two different colors for direction indication. This circuit wont see more than 4V, 100mA.

 

Assuming something simple like a battery powered motor:

For the switching part, have you considered using two SPST switches connected as if they were a single DPDT switch? I think the only annoyance is that without a mechanical coupling of some sort the switches can get out of phase, but there should be no real ham in that happening. Indeed, with teh switches out of phase, you would have the off position.

 

something like this? Just don't keep them both closed or opened simultaneously.

 

I came across many options for spdt and dpdt switching

There's a reason for that. A DPDT switch gives a simple, robust solution. If you use an ON-OFF-ON variety, you can also turn the motor off.

but can this be done with 2 spst and possibly a couple diodes?

You'll need a bit more control logic.

 

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@DickCappels , yes it is battery powered. I considered using 2 spst to create two separate circuits, but like you outlined, it would be very inconvenient without the addition of a mechanical coupler.
@misokopera I'll try checking that picture out. For some reason it isn't loading on my phone.
@dl324 maybe with a few other passive/ discrete components? I would even go for a pre made control board if I can keep it under 15mm x 20mm

 

@dl324 maybe with a few other passive/ discrete components?

Flip flop and an H bridge.

 

And yes, you would probably want to make a mechanical linkage to at least prevent shorting the battery.

A DPDT or as dl324 suggested an ON-OFF-ON switch would be a lot simpler if you can get one of those.

 

would something like this be what I'm looking for to drive it? I looked into the h bridge set up, but like the article states, grounding the 2 and 4 at the same time would cause a battery short.
http://elprojects.blogspot.com/2011/01/bidirectional-control-of-dc-motor-using.html?m=1

Flip flop and an H bridge.

 

would something like this be what I'm looking for to drive it?

That and a flip flop to implement alternate action from the switch.

Circuit in question for the convenience of others:

 

You can do it with S.P.S.T. using two small relays instead of solid state.
Each relay will lock the other direction out when energized.
Max.

 

Here's the circuit with two SPDT configured as a bridge so that they won't short the battery in any position.
Energizing one switch rotates the motor in one direction, and the other switch rotates it in the other direction.
When they are both in the same position the motor is off.
(I didn't have a switch symbol so I had to use a SPDT relay ),

 

@dl324 im reading into this whole single bit logic stuff. I think this is the best option so far. But I'm not sure what type of gate or...transistor? To use. That 'c282' component looked like it was supposed to provide the switch for mitigating a short.

@MaxHeadRoom unfortunately the size constraints limit me to smaller components.

@crutschow unfortunately I have spst switches to work with, and they are the tiny tact buttons. I would use 2 per channel, but this wouldn't work for my design.

 

unfortunately I have spst switches to work with

Yes, I misread your post.

 

How do you want to start and stop the motor?
What control switches did you have in mind to do all the functions?
Do you want two switches, one that starts and stops for each direction, or one switch for direction and one to start and stop.

 

How do you want to start and stop the motor?
What control switches did you have in mind to do all the functions?
Do you want two switches, one that starts and stops for each direction, or one switch for direction and one to start and stop.

The best, and most ideal set up is all normally closed circuits. One button press spins motor cw, another button spins ccw.

I ordered tactile spst switches, one with 4 pins(still spst), and another with just two. After working with a circuit diagram a few hours, I realized this was a mistake and should have gone with dpdt. Unfortunately I cannot locate dpdt In the size I need. I figured a step back and some fresh eyes could sort out a way to wire 2 buttons, a motor, and power source for forward and reverse. But it appears it isn't physically possible with these components.

 

How about a dual coil magnetic latching relay? 2 SPST Tact switches drive the set/reset coils. Keeps its position with no power and through power downs. I've used them in several places like you describe. Here's an example from this search at Mouser:
http://www.mouser.com/Electromechanical/Relays/General-Purpose-Relays/_/N-5g36?P=1z0z1s3Z1yvsbam

 

That 'c282' component looked like it was supposed to provide the switch for mitigating a short.

It's the inverter that prevents the power source from being shorted by having both left side or right side transistors on at the same time.

The text in that schematic mentions NPN and PNP transistors. It looks to me like they were all drawn as NPN. The top pair of transistors are usually PNP and the bottom pair are NPN. That avoids issues with turn on voltages. Like this:

It's something I found on the net, so the inconsistent use of connection dots isn't me...

Also, there's a typo in the transistor numbers in the second paragraph.

The H bridge can be MOSFETs or BJTs. Specs depend on operating voltage and current required by the motor.

 

The best, and most ideal set up is all normally closed circuits. One button press spins motor cw, another button spins ccw.

Here's the LTspice simulation of a simple MOSFET H-bridge that should do that.
The MOSFETs must be logic-level types with a Vth of no more than about 2V maximum.
CW is M1 positive with respect to M2.

 

@JohnInTX I would use those, but six constraints limit that option

@dl324 yeah i noticed the collector and emitter were backwards on a few. And junctions didnt look right on others. I'm going to look over this new schematic by crutschow, it looks like this one integrates the logic needed.

@crutschow thank you! I'm going to look up these listed components to see if I can understand the flow and switching here.