# A Simple Motor Control Circuit FWD RVS OFF

#### Flux007

Joined Dec 5, 2011
2
Hello, Im new to this forum so thought my first post would be a good one. I am an apprentice electronics engineer and would like to find a way to make an apparantly simple circuit.

All I want is: One flick of a switch a motor would spin one way until it hits a limit switch, this would then automatically reverse direction of the motor until it hits another limit switch which turns the motor off. This would be one cycle of the circuit, so whenever that one switch is flicked at the end of the cycle the same switch can be pressed to turn the circuit on.

I thought this would be a simple circuit to make and have produced some which arnt quite right. Using H bridges, and an IC i cant remember. However the main problem is the limit switchs (which ones) and the wiring of them. I have asked many people I would with but no joy so far. Schematics are very much desired.

I apologise for not using many specifics in my brief; I intend on using roughly a 9v powersupply, small 6v DC motor that kinda thing.

Any assistance would be greatly apprecieated as even though the project the circuit was intended for is not going ahead I still want to figure out how to do this. I keep saying to my self it should be straight forward but noone knows!

I shall look forward to you words of wisdom.

#### SgtWookie

Joined Jul 17, 2007
22,230
This should do it for you:

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#### strantor

Joined Oct 3, 2010
6,743
I know sgtwookie just posted an elegant solution but I spent too much time on this not to post. here's what I came up with:

LS1 is normally closed, held open because at the last part of the previous cycle, the limit switch is actuated and the motor stops.
PB1 is held down long enough for the motor to start moving and release the limit switch.
The motor will travel until it reaches LS2, at which point CR2 latches and actuates CR3, which reverses the direction of the motor, until it comes back to LS1 which removes power to the whole circuit (until PB1 is pressed again) and resets the latch so the motor will go the opposite direction again when you push the button
I forgot to draw flyback diodes, but you should use them.

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#### T.Jackson

Joined Nov 22, 2011
328
I know sgtwookie just posted an elegant solution but I spent too much time on this not to post. here's what I came up with:
He's now using a USD 3K software package: Protel SE to draw schematics at lightening speeds.

Nice job. I like both solutions

#### SgtWookie

Joined Jul 17, 2007
22,230
He's now using a USD 3K software package: Protel SE to draw schematics at lightening speeds.

Nice job. I like both solutions
Actually, I had drawn that schematic in Circuitmaker Student a couple of years ago for a Navy Veteran who had a model of a German WWII Tiger II tank that he wanted to animate the tank commander using a remote control:

See the commander in action: http://www.youtube.com/watch?v=tKoNrm9qNCE#t=5

It fit the bill for our OP's task, so I dusted it off and threw it up here; just changed some labels and the notes a bit to make it more generic.

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#### T.Jackson

Joined Nov 22, 2011
328
Something solid state to consider: (should work)

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#### thatoneguy

Joined Feb 19, 2009
6,359
Q3 and Q4 are going to have issues being on, they see the same signal no matter which direction the motor is supposed to turn.

--ETA: The whole H-Bridge is that way, with bases tied together.

--ETA Again - One of your posts just vanished.

#### SgtWookie

Joined Jul 17, 2007
22,230
The way you have connected your H-bridge will result in four flaming transistors about 2 seconds after you apply power, as you will short out the supply. Here is a simulation of what happens; just the operating point values are displayed:

As you can see, there is 835mA flowing through R1, a 10 Ohm resistor. The left, center and right portions of the circuit will respond very similarly. I had to insert R1, as otherwise the simulation would not run; singular matrix due to the way you wired the transistors.

If you want to wire the bases directly together, you have to use an emitter follower configuration. Unfortunately, you'll lose ~0.7v across the be junctions both top and bottom.

You will lose another 0.7v across the diodes.

The switches need to be de-bounced, or the 4017 will have multiple clocks issued.

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#### T.Jackson

Joined Nov 22, 2011
328
Q3 and Q4 are going to have issues being on, they see the same signal no matter which direction the motor is supposed to turn.
There's two inverters now.

Is it right?

#### thatoneguy

Joined Feb 19, 2009
6,359
There's two inverters now.

Is it right?
No, the bases are tied together, so both will turn on on both sides, making a nice short circuit.

Wookie spotted this --> Add a debounce from the switch to the input of the counter, or it can jump multiple times. Usually 10mS is long enough for debounce if you do it with an RC circuit.

--ETA: 4017's Q2-Q9 should be tied back to reset, in case a giltch gets the counter into one of those states/positions.

#### T.Jackson

Joined Nov 22, 2011
328
Better?

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#### thatoneguy

Joined Feb 19, 2009
6,359
You still have the bases tied together. You need to separate the control lines.

You do fine until after the inverters, where you tie the two lines back together again. They need to be separate, 4 wires in 2 pairs. Yours goes from 4 wires to two points.

#### T.Jackson

Joined Nov 22, 2011
328
I think I know what you mean.

#### SgtWookie

Joined Jul 17, 2007
22,230
--ETA: 4017's Q2-Q9 should be tied back to reset, in case a giltch gets the counter into one of those states/positions.
You cannot tie multiple 4017 outputs together, as only one of them can be high; the remainder low. They are not open-drain; they are actively pulled high or low. So, you could just use Q2.

Connecting Q2 to RESET would conflict with S1; when S1 is pressed, Q2 would be pulled to Vcc, damaging the output.

I have a feeling that we're trying to put lipstick on a pig here.

#### thatoneguy

Joined Feb 19, 2009
6,359
I have a feeling that we're trying to put lipstick on a pig here.
True, why not a flip flop to run it all, an SCR to trigger the start, and power removal for the end, with the flip flop for the reverse? Still needs an H-Bridge, but simpler than a counter.

#### T.Jackson

Joined Nov 22, 2011
328
True, why not a flip flop to run it all, an SCR to trigger the start, and power removal for the end, with the flip flop for the reverse? Still needs an H-Bridge, but simpler than a counter.
I am not finding this one easy at all.

I welcome your input in the form of a schematic.

#### thatoneguy

Joined Feb 19, 2009
6,359
See attached. Couldn't find the right MOSFET driver, but any with the 2in/2 out connection and high side driver internal will work.

Start by turning on SCR

Reverses when switch T is hit

Ends and powers off when Switch LimitEnd is hit

Though it does fail on "same switch to stop and start" now that I re-read original post. This was more to show the H-Bridge and T-FF and SCR running it.. It could be rearranged a bit to meet OP's request using DPDT momentary switch.

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#### SgtWookie

Joined Jul 17, 2007
22,230
If the motor is a universal brush-type motor with a commutator, or if the current through the motor is ever stopped for some other reason (like when the motor is being reversed), the current through the SCR will fall to zero and it will turn off.

So now you have a much more complex circuit that won't work.

#### thatoneguy

Joined Feb 19, 2009
6,359
Woops, I had a "Running" LED to the right of the motor to keep it on, but then took it off to post.

I thought it was extreneous (checking various SCRs), but I didn't run the sim afterward. So, Assume there is a green LED from V+ to GND on the right side, and it works.

Only "More Complicated" in the sense of using MOSFET Drivers on every MOSFET.

All better, now with COLOR CODED Power and H-Bridge control lines.

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