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Toggle switch for linear actuator Answered

Hi I'm new here - I'd be very grateful if someone could give me some tips. Apologies if I'm asking something that's already well covered. If so, please direct me.

I'm building a TV lift cabinet that will use a 12V linear actuator to lift the TV. It is likely to take somewhere between 1-2 minutes to fully extend and retract the actuator. I want to be able to control the raising and lowering of the TV using a 3-way toggle switch that returns to the central 'off' position by itself. I want a nudge of the switch in one direction to operate the actuator for, e.g., 75 seconds (by which time it should be fully extended), and a nudge in the other direction to operate the actuator with polarity reversed to retract it. The timings are not critical, as the actuator will shut off automatically when fully extended/retracted.

Many thanks, Chris

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Jack A Lopez
Jack A Lopez

22 days ago

I think the usual trick for switching the direction of a DC motor, without using transistors, is to use two relays, one relay switching each motor terminal.

If you do like transistors, then the usual trick is a H-bridge.

In addition to the relays (or transistors), there are usually two, what are called, "limit switches," and the job of those switches is to stop the motor somehow, (either interrupting current to the motor directly, or by messing with the relays (or transistors) that switch current to the motor) when the door, or window, or whatever the thing is, has reached either of two limits to its travel; e.g. totally up, or totally down.

I found a Youtube video, of a simple design of the kind with two relays. This design is not complicated enough to do what you want, but I think it is instructive. Here:



Also I thought I would try drawing some circuit diagrams to kind of puzzle this out. I decided to try drawing these using gEDA (www.geda-project.org)
because relay circuits are kind of tedious to draw with pencil and paper.

Messing around with the gEDA schematic editor was a little bit tedious too, since I rarely use it, but I came up with some ideas to try to make a circuit with relays that would latch (i.e. stay on) for to give a behavior we want, e.g. pushing a "up" button causes the motor too turn on, stay on, and only turn off once the "up limit" switch has been pushed open.

There are two pictures attached. The first version has push buttons: {up, down, stop} and this seemed to me to be the kind of the way I would do it.

The second version has that double throw (or maybe it is triple throw?) momentary switch you wanted, ( I mean the kind that springs back to a center position, not connected to anything) plus a stop button. The stop button is there, for if you change your mind while the motor is still moving.

Neither version is totally foolproof, because I think there is a way to kick both relays on, which stops the motor, but is otherwise a harmless state. The way to get out of the state with both relays on, is by pushing the "stop" button.

up-down-v1.jpgup-down-v2.jpg
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Orngrimm
Orngrimm

23 days ago

Not sure what you are asking for to be honest... Sounds like you have a quite good plan...
Please correct me if i am wrong:
You are looking for a method of setting a manual (!) operated 3-way-switch to the neutral center position if the cabinet is fully extended or fully retracted?

If i would tackle this problem, i would go with 3 momentary switches (Up, stop, Down), 2 sensors (1 for extended, 1 for retracted) and slam a 1$ Arduino and 2 FET to it and be gone with it...

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sirsh42
sirsh42

Reply 23 days ago

Thank you for your reply. Sorry I wasn’t clear- I want the “up” nudge to provide power to the actuator for a set length of time (the time it takes to extend the actuator) and the “down” nudge to do the same with the opposite polarity to retract the actuator. It’s the timing I don’t know how to achieve in the cheapest way possible.

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Downunder35m
Downunder35m

Reply 22 days ago

Isn't it good how added details can make things easy to understand.... :)
Even better if there is an old fart driving a 30 year old 4WD ;)
Back in it's glory day it has feature not many other cars out there had, for example ELECTRIC WINDOWS - HINT HINT
Go to your local car wrecker and go through what they have to find window switches that reset to neutral.
Most of them will do anyway but some like on old Mitsubishi's have a locking function for up and down that resets once the motor draws too much power.
Avoid the last ones as the have too many connectors.
If you can find a set in a center console good, if the door one comes with a separte plate where it sits it even better.
Either way, take them as well to have a good template for you mods on the TV unit.
In some old cars you will find these switches with a cover plate included in the switch, they would be my prefered option as you just need to push them into a slot on the TV unit to look good already ;)