controlling wheelchair with micro microcontroller sensor

[dmehling]

I am trying to figure out an alternative way of activating a switch on a wheelchair.  The currently used switch is used simply to change functions and is connected with a 3.5 mm connector to the input control system.  Here is a picture of what I am talking about:

http://www.infogrip.com/product_view.asp?RecordNumber=165

I would like to see if I could use some kind of touch switch or sensor instead of the mechanical micro switch.  The best way to do this is probably to connect the sensor to a microcontroller, and then attach the microcontroller to the wheelchair input system with a cord that has a 3.5 mm plug.  How would I attach something like that to my microcontroller?

[Soeren]

Hi,

I would like to see if I could use some kind of touch switch or sensor instead of the mechanical micro switch.

That should be quite easy, as it seems to be a simple switch function (i.e. closed when pressed and open when released).

The best way to do this is probably to connect the sensor to a microcontroller, and then attach the microcontroller to the wheelchair input system with a cord that has a 3.5 mm plug.  How would I attach something like that to my icrocontroller?

If you don't have the microcontroller allready, then there is no need to include one.
A touch sensor is easy to make (remember, if it's for a disabled person, it should be properly build and safe) and there's a good chance that an open collector transistor on the output can replace the actual switch contacts (if orientated the right way round).

Tell us what exactly it's going to control and it will be easier to help.

For a quick test to see if a transistor will control the input in question, you can try bridging the contacts (the poles in a similar 3.5mm connector) with a diode. If it doesn't work first time, try turning the diode around.

[dmehling]

I appreciate your helpful advice, but most of what you said went over my head.  Let me simplify what needs to be done.  The switch I was talking about connects to a module on the wheelchair that controls all of the driving functions as well as functions that control seat adjustments.  When the wheelchair is turned on it is in drive mode, and a single press of the switch puts it into speed selection mode while a second press puts it in to seat adjustment mode.  That's all the switch does.  The current user of the chair has gotten to the point where it is very difficult to push this switch.  I need to figure out how to wire this switch up to a microcontroller so that input received from another switch or touch sensor will simulate a press of this switch.  If that is too complicated, then I will simply get a small servo that will push the switch based on input given to the microcontroller.  This is in inelegant solution but probably much easier.  Perhaps what I need help with at this point is finding a touch sensor.  Any suggestions?  It needs to be able to detect a slight touch or a slight amount of movement.

[Rebelgium]

There are capacitive switches, and LDR s. (Light dependant resistor - you go over the resistor with your finger, less light, microC recognises it ...)
These are two possible solutions for you.

[dunk]

hi Dmehling,
there are only 2 connections going to the switch you want to replace right?
the chances are that that one connection goes to ground and the other to an input pin of the wheelchair's existing microcontroller.
test which is which with your multimeter.
the input pin should have a voltage of whatever the wheelchair's microcontroller uses.

once you have this part figured out it will be easy to drive the wheelchair's input pin with an output on your own microcontroller, although as Soeren says, most sensors yor might use in place of the switch wouldn't really need a microcontroller to interface them.

dunk.

[dmehling]

Can you briefly explain how a capacitance switch works?  I'm still pretty new to robotics/electronics and I have not heard much about that kind of switch.  Also, where can I find such a switch?