load sensed switch

[hairbear]

Hi i am trying to build a target changer it runs on 12v motor with a pulley which runs a carriage back and forth what i am trying to do is stop the carriage when it reaches either end of the travel the professional one's stop automaticaly at either end at the far end their is no electroncs just a pulley so i think that when the motor loads up it cuts the circuit any help would be great thank you

 

[Mike odom]

put a resistor in line with the motor drive and monitor for voltage across this resistor. When it gets to the motor stall current, shut it off. What are you using for motor drive?

 

[ClydeCrashKop]

Garage door openers use a pin / bump on the chain to open a normally closed switch at the ends of the travel. Then a push button switch to override the normally closed switch will start it again to go to the other end.

 

[Mike odom]

Garage door openers use a pin / bump on the chain to open a normally closed switch at the ends of the travel. Then a push button switch to override the normally closed switch will start it again to go to the other end.

*He doesn't want to use a switch

 

[MikeMl]

You need three switches. one is a Single Pole Double Throw toggle switch that is used to control where you want to the carriage to go. Two are Normally-Closed Single Pole limit-switches mounted such that the motor-driven carriage opens the switch when it reaches either the Left limit or the Right limit, respectively. The limit switches should be the kind that have an arm and roller, like this.

 

[dr pepper]

Another approach if the motor can withstand being stalled for a few seconds is just an adjustable thermal circuit breaker, set the trip point 25% or so above the trip point, when the motor stalls at the end of travel the current goes up and the breaker trips stopping it, reset the breaker and your away again.

 

[Mr RB]

There's a simple circuit here;
https://www.romanblack.com/current.htm
that uses just one transistor and a few parts and does exactly what you need. It provides a 0-5v output suitable for connecting to a digital input on a PIC etc.

 

[Reloadron]

Most of the indoor ranges that I shoot at use the same circuit that Mike posted to control the target carriage travel. Generally away from and towards the shooter but back and forth would be the same. Switches are used more prevalent only because target carriages were transitioning targets long before the uC came along. Mr RB also has a very good circuit that senses current and let's a uC do the job. To my thinking either circuit would work just fine.

Ron

 

[Mr RB]

My circuit does not neccessarily require a microcontroller. It's output is normally at 5v, and drops to low, near 0v, during the overcurrent situation.

In a manual system that could be used to drive a relay coil etc, so in overcurrent situation the voltage drops and the relay coil drops out. If the relay is set up for self-latching, you could press one button, relay latches on, then at end of travel the circuit drops the relay out.

 

[Reloadron]

My circuit does not neccessarily require a microcontroller. It's output is normally at 5v, and drops to low, near 0v, during the overcurrent situation.

In a manual system that could be used to drive a relay coil etc, so in overcurrent situation the voltage drops and the relay coil drops out. If the relay is set up for self-latching, you could press one button, relay latches on, then at end of travel the circuit drops the relay out.

Good point there Mr RB. I should have worded my post better. Wonder what happened to the OP?

Ron

 

[Mr RB]

Another "one-post wonder" I think. He probably got free help somewhere else that was slightly better than our free help.