Advice on latch circuit

[Ted1953]

I am building clock and need a circuit, including part numbers, to start a 30 VDC motor off of a position and then stop it at another position all automatically. The circuit should run on a 9vdc battery. I would prefer a friction less solution such as the sensor moving past magnets to initiate start and stop signal.

 

[Ted1953]

Ok no part numbers, but at least part types, thanks for your assistance!

 

[alec_t]

What is the motor type? Brushed DC, BLDC, stepper?
What current does the motor draw when stalled and when running at speed?
How many revs will the motor do between the start and stop positions?
A 30V motor sounds quite chunky and likely to have substantial inertia. Doesn't seem ideal for driving a clock.
Are you relly intending to run a 30V motor from a tiny 9V battery?
Your thread title seems unrelated to motor control. Can you edit it?

 

[Ted1953]

Alec-t, the motor is installed and runs fine, it actually lifts a heavier arm to rewind clock vs run clock. Anyway it is working with a mercury switch. But the mercury switch turns the motor on fine and after 0.1 inch travel, the switch opens and motor stops. I need about a 2 or 3 inch travel time on the arm so that's why I'm thinking a latch circuit to keep it energized longer than the mercury switch is doing. 9vdc driving 30rpm 12vdc motor, sorry on 30v. Again I'd rather have the switch change states due to passing a magnet to energize then pass another magnet to energize. I could place the magnets a distance apart to get the exact distance of arm travel I need.

 

[crutschow]

I'd rather have the switch change states due to passing a magnet to energize then pass another magnet to energize.

Could you clarify that statement.

 

[Ted1953]

Imagine holding your arm out in front of you parallel to the floor. In your hand is this switch I am asking for. When your arm drops on an arc from your shoulder a bit, this switch turns on and energizes a motor that runs and raises your arm towards the ceiling about 30 degrees then shuts off. I'm looking for a switch activated by magnets mounted on something your hand passes as is goes up and down. I'm currently using a mercury switch, but it stops as soon as your arm goes up 1 degree instead of staying on.

 

[Ted1953]

Another example of what I'm looking for is an elevator switch. When you press the button the light stays on until you reach the next floor. In my case I'd like the light to go on because of a magnet that senses the elevator came down to say floor 1. Then the elevator, on it's own goes up to floor 2 and stops again due to picking up another magnets field.

 

[alec_t]

A magnet on the arm, a couple of reed switches at the top and bottom limit positions, a 555 IC for the latch function, two resistors, a back-emf suppression diode and a power MOSFET (if necessary to handle the unknown motor current) should do the job. Methinks a PP3 9V battery won't have a long life.
Presumably the motor can reverse under gravity rather than under electrical power?

 

[Ted1953]

Thanks guys, found a tech locally, electrolytic capacitor in parallel with motor gives me 5 sec decay run time, plenty for 30 degrees. This battery is on another clock and lasts about 3 months under a similar set up but with mechanical switches.

 

[Ted1953]

Alec, sorry meant to say yes the arm falls by gravity. Thanks for taking your time to give me input, appreciate it!