Yes, just put this question on MEA as well...lets see who's smarter :P No, I'm actually looking for an answer for this.

Hey,

Another retarded question I had...

So I've decided to build a linear actuator out of some parts I had lying around, and need a control circuit for it. A H-bridge and a SPDT switch is simple enough to build, however I need to incorporate a limit-switch onto the system so it doesn't tear my boot apart. I have numerous 12V relays on hand, so I'm not going to build one with fets.

Ideally, I'd want to be able to flick the siwtch into 'up' and have the panels move up and stop automatically. Then, when I flick it to down, it will do the same thing, and stop. I'd be able to stop the thing mid-way by flicking the switch to 'off'.

Say the 4 quadrants,
1 - Top left
2 - Top right
3 - Bottom left
4 - Bottom right

1 & 4 closed = Clockwise
2 & 3 closed = Counter Clockwise

Top side being 12V+, bottom side being GND.


If I have a microswitch, that closes, and turns on say, one side of the H-bridge (1 & 3), it will stop the motor, but how would you open up relay 4, to stop it wanting to spin again?

For some reason I'm thinking I can solve this with another two H-bridges linked from the microswitches? That's like, 12 relays, lol...surely there's a better way.

If I was really smart, it would be cool to push a button, have it rise up and stop, then push the same button and lower itself, and stop.

Yep, use SCR's or make an scr from a latching relay...

Or.....

figrelliauto site, and just buy the micro-switch which will do the job for you :woot:

For $26 its not half bad.

http://www.firgelliauto.com.au/product_info.php?cPath=63_70&products_id=83

How are your programming skills?
Could use a simple micro to control the H Bridges. Its intelligent then... if the top limit switch has been tripped, it will know that if you press the button it is to go down again.

Did someone say programming!

To be honest, my first thought was programming, however I have never done any useful programming (C,VB, Delphi) but forgotten all of it. What would one need to make something like that on a chip?

Someone on MEA kindly posted a pic consisting of two relays, two microswitches, that are normally closed. I then connect that to a spdt switch and it will allow me to flick the siwtch either up or down, and the panel will keep moving until the limits, where the microswitch actuates, opens the contact and breaks the circuit, only allowing you to move in the other direction. It seems a lot simpler than programming. My only thought is...how do you get it to reverse the polarity and/or integrate into the h-bridge?

I was going to suggest a PIC, a cheap ICSP programmer (that you could make yourself) and a freeware copy of picbasic pro and picprog.exe but the OP wanted to use relays :)