Motor Control w/ Limit Switches Based on Voltage

Thread Starter

cecijjoy

Joined May 29, 2018
4
Hello! I'm new to electronics, and this is my first time looking at limit switches (and I must say I don't understand them well at all).

I have a motor which runs on a voltage from -15V to +15V where the exact voltage determines the speed and neg/pos determines forward or reverse. I want to add a limit switch to my circuit (ultimately a pcb) which prevents the voltage from going above +/- 15V but allows the user to change the voltage in the opposite direction. For example, if the user tries to increase the voltage past +15V, it will not allow that but it will allow the user to turn the voltage back down to +14V.

I have no idea what possible designs would be for this. I've found designs which can flip the direction from forward to reverse, but I don't want this...preferably the motor just continues at the +15V speed and is prevented from increasing there but allowed to decrease.

Thanks!
 

MaxHeadRoom

Joined Jul 18, 2013
22,332
Not sure of your present system, but if you want to control/limit RPM range.
Voltage monitoring is not an exact way.'
IOW, you may detect a certain voltage, but that does not necessarily indicate the rpm unless the load is exactly constant.
Max..
 

Thread Starter

cecijjoy

Joined May 29, 2018
4
Not sure of your present system, but if you want to control/limit RPM range.
Voltage monitoring is not an exact way.'
IOW, you may detect a certain voltage, but that does not necessarily indicate the rpm unless the load is exactly constant.
Max..
It doesn't need to be exact, just a built in hardware backup. Will be using a digital potentiometer, and software should prevent users from going above 15V, but want a hardware switch just in case. What would you recommend I look at as far as limiting the RPM range? I'm not sure what kind of circuit to consider.
 

Thread Starter

cecijjoy

Joined May 29, 2018
4
What is the nature of your present controller?
Software etc?
Max.
So I'm trying to design a motor control shield for an arduino mega. This will simply allow a digital pot (or possibly op amp circuit...that would be down the line) to control voltage given to the motor.
 

be80be

Joined Jul 5, 2008
2,051
You kind of lost here a motor doesnt change like your saying.
You can control speed 0 to 15 thats easy.
Next part you have to reverse the power supply to change from forward to backward then control its speed 0 to 15 volts if you want to just call it that.
What you really do is use pwm with a voltage limit of 15 volts.
 

dendad

Joined Feb 20, 2016
3,712
To limit the motor volts to 15V, just use a 15V power supply.
And then for motor speed, PWM is the only way to go. And an H bridge to control the direction so a +/- supply is not needed.
To limit the RPM, you will need to monitor it with a rotating magnet and Hall sensor, or an optical chopper. Then the PWM is automatically adjusted by the Arduino to control the speed.
But it is a little difficult to say for sure as you have not posted much info.
Do you need a motor driver or is this a retrofit to an existing system?
What power supplies are available?
Motor current?
 
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