Hello everyone,

I work for a Point of Sale display company and we have a need for a circuit that can control how a battery connects to a small motor. We need the motor to move right for a small time, then reverse direction.

I have proposed we use a simple circuit to reverse the polarity of the power from the battery and then after a specific amount of time, reverse it back...and so on and so on forever.

Can any of you guys point me in the right direction? Can this be done simply with diodes and capacitors, or will a programmed Op Amp be needed?

I am a novice, so be kind.

Thanks!

Tyler

 

if its a small dc motor, you can use a 555 timer and relay.

 

if its a small dc motor, you can use a 555 timer and relay.

yes, very small motor.

... Is there any schematics you might be able to point to? Thank you SO much for the quick reply.

 

There are a whole raft of previous posts here that do exactly this.
Max.

 

Building on Dodgydave's idea of using a NE555:

The article at the URL below explains the circuit.
http://www.next.gr/circuits/Bi-directional-motor-l37017.html

 

here is one suggestion,

http://www.circuitstoday.com/wp-content/uploads/2009/06/bi-directional-motor.jpg

edit, you beat me to it Dick...

 

Also do you need end stops, or does it matter if it over runs, i.e. no physical stop present??
Max.

 

Also do you need end stops, or does it matter if it over runs, i.e. no physical stop present??
Max.

Whats happening is a "head" is turning left and then right. there is no absolute location it must stop before reversing, but it would be a good idea to have it in the same place each time so the head doesn't go too far over time.

(I have to thank all of you for such fast and informative responses! Quite an amazing forum!)

 

You can put a 2 limit switches in series with the motor leads, one at each end of travel, a diode across each allows reverse without anymore switching.
Max.

 

Or forget all that and just do it mechanically..
Back and forth can easily be accomplished with the motor turning in one direction only..

 

Or forget all that and just do it mechanically..
Back and forth can easily be accomplished with the motor turning in one direction only..

We are exploring the mechanical option as well, but it gets far more complicated and the more moving parts you have the greater the risk of failure. An electronic option would also be far cheaper.

 

best solution is to use the timer for the motor as a flip flop, with a limit switch at each end of the turn, this would flip the direction of the motor

 

Since you are running a POS you should already have an MCU running the thing and hopefully a couple free ports. I'd consider going with a small stepper motor maybe powered by an off the shelf $3 L293 or some other driver or if it is a regular brushed DC motor a dedicated driver IC similar to those used in cassette, CD-Rom, and VCRs where all you have to do is send a drive signal to the chip. I myself have an LB1943 from my junk pile that I have been playing with... shouldn't be too hard to get something similar.

http://www.datasheetcatalog.com/datasheets_pdf/L/B/1/9/LB1943.shtml

 

Circuit doesn't work... probably an error on my end, Here is the layout I created for my construction. When I hook it up, the motor runs, but doesn't switch... I also think I smelled some burning smell, so somethings not right:

 

your motor is not on the wipers of the relay, looks like your supply shorts out, is pin 3 changing output going high and low, if so the 555 is working, if not oh dear.....

 

your motor is not on the wipers of the relay, looks like your supply shorts out, is pin 3 changing output going high and low, if so the 555 is working, if not oh dear.....

Here is a pic of the relay. The wiper seems to be on the right side not the middle:

 

ok, get a voltmeter on pins 1& 2, is it rising and falling,and is pin 3 changing output. Also looks like the transistor is drawn wrong, C E reversed.

 

ok, get a voltmeter on pins 1& 2, is it rising and falling,and is pin 3 changing output. Also looks like the transistor is drawn wrong, C E reversed.

voltmeter with neg on "1" and Pos on "2" reads a slow increase in voltage slowing down at around 4-5v. So its not rising and falling.

As for the transistor, I'm not sure why you think its backwards. The Emmiter connects to the diode and the Collector goes straight to Positive battery terminal.

 

Your using the transistor as an Emitter follower, thats ok , pin 2 rises upto 2/3 supply then discharges to 1/3, what is the supply voltage and is it a power supply or battery.

 

Your using the transistor as an Emitter follower, thats ok , pin 2 rises upto 2/3 supply then discharges to 1/3, what is the supply voltage and is it a power supply or battery.

As I said, pin 2 is not dropping...

power supply is 8 D Batteries at 12v