Make a switch operate at a certain voltage

[Andy Scott]

Here is an easy problem for you guys (probably). You have probably answered questions like this before, so sorry for any repetition here.

I am trying to design a circuit whereby at a certain voltage a switch will operate allowing a linear actuator to extend.

My idea currently is that you have a circuit with a variable resistor allowing you to control the voltage on the circuit.

What I want to happen is for when the voltage reaches a certain point, the switch to close enabling the actuator to operate.

The thing is I just have one power source. So both the actuator and the switch would have to be on the same circuit. Also this would be a very low power circuit, so the actuator would need to operate at very low power. In fact an actuator might not even be the best solution.

Any advice or criticism is welcome.

EDIT: By the way if you instead wish to direct me towards some good reading material, that is also welcome.

 

[garublador]

FWIW, we'll need to know the voltage source you're talking about, what "certain voltage" you want it switched at, what actuator you want to use, what the actuator is doing, and what you mean by "very low power." I've probably missed some other things, but just describing, in detail what you're trying to do and the specifications of any parts that are required is probably best unless you're OK with just getting a starting point. Without a lot more specifics it will be hard to give anything but a vague answer, but here goes.

At a high level it sounds like you want your voltage to go into a potentiometer (variable resistor). The voltage out of that divider will go into a Schmitt trigger, which is a device that takes a slow moving signal to a discreet on/off signal. The output of the Schmitt trigger will go to a transistor which will control the coil of a relay. The relay will turn the actuator on and off.

 

[Andy Scott]

Thank you!

For more information I imagine the voltage to vary between 0V and 6V ranging between 0mA and 200mA. The objective is to be able to use the potentiometer to define at which voltage the Schmitt trigger will send the "On" signal.

Thank you for taking the time to respond.

EDIT: The purpose of the actuator is to simply unblock a shaft on a strong spring which will then punch downwards. The actuator or other device simply needs to be able to hold the shaft in its locked position then reliably move out of the way to allow it to extend. I am not certain an actuator is the best solution. I simply need the device that will draw the least power in this respect while operating reliably.

 

[garublador]

I'm a bit confused now. Will you have a constant voltage or is the only power you're supplying the varying 0-6V supply? I assumed you have some constant voltage, like 6V, and you'd turn the potentometer one way and eventually the actuator would turn on. When turned back the other way it would turn off. If the only input voltage you have is the varying 0-6V supply then my solution might not work and more information might be needed.

 

[Andy Scott]

Thanks Garu. The only voltage supplied is the varying 0-6V supply, this will vary randomly. My objective is to be able to use the potentiometer to govern the voltage at which the device holding the shaft in place (see previous edit) will withdraw. This device will need to be powered solely by the same 0-6V supply! There is no other power source. Maybe this is trickier than I thought.

The shaft that extends is powered by the spring, which is put into position manually, so is not connected to the circuit.

Thanks for your help so far.

 

[davenn]

The control circuit will need a stable supply
A comparator IC could be used to detect a voltage level and operate a transistor switch/relay

here's a starting circuit to give you an idea



cheers
Dave

 

[Andy Scott]

Thank you!