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Simple Design Help.. Any advice appreciated!

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Hey all,

I've been struggling with a relatively simple concept and it has been a big pain. I am making a simple automated system with two optical sensors and a sliding peice.

I want the object to start in one place and once the drive circuitry is enabled for it to travel (linear), it will move until the other end. This end an optical sensor triggers at its presence, and then reverses the motor. Once this gets back to the original spot, I want it to stop until it is triggered again.

I want to keep the parts count as low as possible. I have thought about using some flipflops, but I am concerned about its initial state and it not knowing which direction to turn the motor. The motor's control is actually quite simple, 0 for forward and 1 for reverse on the same pin.

If you could help me out with a solution with under two chips, that would be great!

ok, here is a start uses only one IC, a flip-flop, 4013
i understand that you have something to turn the motor on of of...ok?
here is the schematic.
you start the motor by putting a 1 to TRIGGER. even if the first sensor has light on it, the motor will not stop, so it runs untill light falls on SENSOR1 wich will reverse the motor and enable SENSOR2. when light falls on it the motor stops and you need another impulse on TRIGGER to start it again.
i asumed that the sensors are light dependent resistors.


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ok, now if i understood what you want corretly.
you start the motor to go forward in place A. it travels to B where some loght goes on the sensor and the motor reverses. then it travells back to A where it is what? another light sensor?
here are some questions....what type of sensor do you use?
you have something like a light beam and when the device interrupts it the motor reverses or you get light on the sensor when the motor arrives in point B? the circuit is intended for the second type, but if you need something different tell me and ill modify the circuit.
and one last, what will make the motor stop? another optical sensor?

Thanks a lot for the circuit, I have looked at it and I think it will work.
I am actually using an optical switch, not anything resistive. I will do some simulation today to make sure that it works before I PCB it.

Thanks a lot!!!!


I will post my results when finished if there is anything significant.
well, the idea is that what ever sensor you will use , it has to generate a 1 to the inputs.....
also you may want to change the output, the transistor and the resistor acording to your motor....
I am a little confused.. I am simulating the circuit, but I really don't like the package (multisim) so I might be doing something wrong. The outputs aren't seeming to be changing states..

Doesn't the clock signal need to activate any input on either set or reset for the output to change states?


i tried it in cir maker and it works, i tried only the digital part and put some logic probes at the outputs, and it works just as i intend.
hope you will make yours work too.
Hey there,

I simulated the circuit in circuitmaker too, but I cannot get it to work. Initially, the 5V is on the Set for IC1A, which causes the direction to move forward, which is correct. Then the trigger is pressed on and off, which causes the motor to turn on and to maintain the direction. Both the trigger and the first switch are off now, and the second switch is set high when the object arrives, this causes the motor to turn off and the direction to be set forward still. This is opposite what I want, but I cannot just reverse it, it will not work for the first states.

Tell me if this makes sense.. I did one bad thing... I removed the diode, is that crucial? It says it will not simulate with it.

Hi Steve,

I looked at your query, and had a little think.
Ive drawn a suggestion for you,
and heres a brief few words as to how i think
it would operate.
The circuit is drawn at rest, and as you can see,
the positive conection has nowhere to go, the press
button is open, and the reed switches are both open.

The motor driven piece is positioned to obscure the
light from light No1 although light No1 is not lit,
nor is Light No 2.

The activator presses the press button, and the motor
moves, both lights light, both reed switches operate,
and the transistor delivers a LOW to the moter sensor.

The activator releases the press button, the motor
continues, reed switch No1 is now held by current
through 'S' light sensor No1.

The motor reaches light No2 and obscures it, causing
reed switch No2 to open, this causes the transistor
to deliver a HI to the motor sensor, and causes the
light No2 to go out, the resistor across the light
may not be needed, it is to ensure a low at the
transistor output when the light goes out.

The motor then goes into reverse, and would not obscure
light No2 any more, but the lamp will not light cos the
reed switch is open.

The motor then runs back to its start position, and
obscures light No1, which causes the first reed switch
to open, and the circuit is then at rest.

I hope this meets with your approval,
if the motor logic can be easily reversed at the motor,
then the transistor may not be needed at all,
in which case the circuit would be quite simple
to construct.

Best of luck, John


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Wow John, what a great plan, I have been pondering also and I wish I could be the one to come up with that, it is a really neat idea!

I am going to start finding parts for this and I want to build it as soon as possible, I will keep you updated


Thanks very much for all your thoughts and time with my post, it's appreciated!
Hi Steve,

Thanks for replying.
I nearly went boss eyed trying to follow what bit does what!

Even when i had drawn it up,
i had to go over it again and again just to be sure i got it right!

You may not need the transistor at all,
if the logic can be reversed at the motor.

Regards, John
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