on off switch under membrane

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fred_b

Member
I am working on putting my picaxe based project into a plastic enclosure.

I plan on having the control buttons and on/off switch protrude about 1-2mm through holes in the top face, which will be covered with a printed membrane overlay.

I have been searching for a few hours for a good on/off switch that will work for this.

I need the switch to turn on after one press and maintain contact. Then, a second press would break the contact. I understand this to be called "latching"?

The problem I see, for all the latching switches I have found, is that the button latches "on" at a lower position (height) than when it is latched "off". I need the button height and travel distance to be constant I think for it to work under the membrane.

Anyone know what should be used for this?

Thank you for your help.
 
R

RexLan

Senior Member
Software -

Also, mounting the switch will be critical and very, very difficult. If possible, you may be better off with a miniature panel mount on/off switch and mount it in the case with wire leads back to your PCB.
 
M

Marcwolf

Senior Member
Hi There

Ok - thinking outside of the envelope

Hall effect sensor and magnet. I have used this in a 'Data Glove' where I have needed a switch link mechanism that will work unser a couple of layers of clothing.

The Hall Effect can be hooked up tp a ADC pin adn monitor the voltage level when the magnet is brought close. When a threshold is reached the PICAXE sets a flag to ON thus acting as a on switch
Touch again and the Flag is reset.

Hope this helps
Dave
 
H

Haku

Senior Member
Before I got into microcontroller programming I wired up my bike light setup using DPDT switches & DPDT push buttons to allow high/low, on/off & a momentary high-beam. The setup works really well but the DPDT push button switches cost over £5 each!

DPDT latching push button switch from Farnell, the switch top remains the same height wether it's in either position - http://uk.farnell.com/apem/8646a/switch-dpdt-latching/dp/1082340
But for that price you could buy an 08M + momentary microswitch, program it as a latching switch and have spare change! :D

Hall effect sensor or reed switch are a good idea, I've seen a waterproof torch that uses a magnet in the external slide switch to activate a reed switch on the inside.
 
D

Dippy

Moderator
Using a Hall Effect into ADC means consuming power when the device is OFF - very inefficient for a bettery powered device.

Other options.
1. The 2 transistor method. MOSFETs for super low power.

2. The enable a regulator method.

3. The JK flipflop method which will allow a single button (cheap pushbutton) on/off.

4. Running the PICAXE in micropower mode until a button is pressed.

5. I'm not sure which PICAXE will support this, but running the PICAXE in Sleep and interrupting from Sleep. I've done this numerous times with PIC and had good results.
(Make sure peripherals are OFF)
 
I

inglewoodpete

Senior Member
fred_b said:
I need the switch to turn on after one press and maintain contact. Then, a second press would break the contact. I understand this to be called "latching"?
Click to expand...
I have never seen a stand-alone latching tactile switch. All of the ones I've seen use software or dedicated logic hardware to create the function from an SPST membrane or tactile switch.

Something like this should work with appropriate software. The circuit is not mine - I've just copied the URL from another thread. Self-switching power down circuits have been discussed many times on the forum.

The circuit described can be used with short-action SPST switches like this: Altronics tactile switch example. They come in many different sizes and actuator lengths.
 
K

KMoffett

Senior Member
Hey, that's my circuit :), and it worked well. It was programmed for both "push-on/push-off" and "push-on/timed-off"

Ken
 
D

Dippy

Moderator
Excellent.
A simplified version can use 2 buttons giving Push-On & Software/Push Off . (I'm not being rude :) )

But there are a number of variations... the oldest going back 10 years with Parallax Stamp.
Sorry KMoffet, I didn't mean to suggest that you didn't invent it , but you didn't ;)

As fred_b has disappeared I can only assume he's found a switch.

Perhaps even a piezo disk which when thumped 'harvests' enough to trigger a MOSFET.
 
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