DIY membrane switch suggestions needed

[Imagewerx]

Right,here's what I'm trying to do. I've got a VW Golf mk.4 that has had the conventional mechanical door handles removed from it and replaced with an electically operated solenoid,the solenoid in question is not really a solenoid but a motor and gearbox (it's used to remotely release the fuel filler flap on the same car if you need to know).
At the moment as shown below it's operated by an infra red beam break unit that fires the solenoid when you put your hand in and break the beam (it's switched off when the alarm is armed).....

**broken link removed**
**broken link removed**
**broken link removed**

It's just a standard off-the-shelf kit from Maplins which I spent a lot of time testing this on the bench before going anywhere near the car with it so knew it was capable of doing what it had to do lots and lots of times.The problem I have now it's on the car is as I thought might happen is it's very sensitive to dirt on the IR tx and rx causing the door to open when it's not supposed to,not when the car's being driven though as it's switched off as soon as I turn the ignition on.As I've yet to use the car with them fitted in heavy rain I can only guess at what's going to happen,but I don't think it'll be as reliable as it needs to be.

So...................what I've decided is to simplify it as much as possible and have just a switch and relay to fire the solenoid,but I'm limited to a depth of about 5mm max.I've been looking at some ultra low profile tactile switches,but once I've mounted them on a PCB and put some sort of waterproof covering over the top of them I'll have used up all of that 5mm.
My plan is to use or make some sort of membrane switch,and as I can't seem to find anything commercially available the right size it looks like I'm gooing to have to make one.

The main criteria is that when closed it must be as close to zero Ohms as possible as it has to drive the relay which draws about 50ma without any other associated circuitry.All Google results suggest the idea with conductive foam but as that only drops to about a few hundred Ohms that's out of the question.

Sooooooooo........... has anyone got any ideas how I can do this or even better to save me some time which I don't have a lot of at the moment,is there any off-the-shelf product I could use? The most important things to remember are a maximum thickness of 5mm and it it must be able to handle more then 50ma.

Thanks in advance,Chris.

 

[mramos1]

Some flat spring steel you press on a contact point (like inside a reed relay) and a rubber skin over it. That would be simple and low profile.

What you have now will have dirt issues, also rain/moisture and more. Cool idea for inside projects though.

 

[jimlovell777]

You'd probably find this to be a suitable solution Atmel Products - Buttons, Sliders & Wheels - AT42QT1010

They even offer an automotive qualified part Atmel Products - Buttons, Sliders & Wheels - AT42QT1110

 

[cobra1]

hi, where abouts in the world are you??

i can make a switch to your specs if you need one.

 

[Imagewerx]

Some flat spring steel you press on a contact point (like inside a reed relay) and a rubber skin over it. That would be simple and low profile.

What you have now will have dirt issues, also rain/moisture and more. Cool idea for inside projects though.

That sounds like the easiest way,think I was trying to make it too complicated for my own good.

You'd probably find this to be a suitable solution Atmel Products - Buttons, Sliders & Wheels - AT42QT1010

They even offer an automotive qualified part Atmel Products - Buttons, Sliders & Wheels - AT42QT1110

Thanks for those suggestions,but as they're capacitive it'll need the circuitry that goes with it which I don't want to do,I need a simple on/off switch that I can put 12 volts through.

hi, where abouts in the world are you??

i can make a switch to your specs if you need one.

I'm in England,thanks for the offer but as with everything else on my car this is a 100% DIY project.

Chris.

 

[cobra1]

im in england too, whereabouts you from??

if you want any info i can help you out with regards to the switches, im a toolmaker so i know how to make almost anything lol

 

[Hero999]

Wait a second, so you'll no longer be able to manually open the door?

If that's true, it's a really bad idea.

 

[Imagewerx]

im in england too, whereabouts you from??

if you want any info i can help you out with regards to the switches, im a toolmaker so i know how to make almost anything lol

West Sussex near Gatwick airport,and yes please any suggestions you have on how to make a VERY low profile switch would be very much appreciated.

Wait a second, so you'll no longer be able to manually open the door?

If that's true, it's a really bad idea.

If I get a flat battery I can get in like this (the rear wiper used to be here).......

**broken link removed**

And in the event of an accident an inertia switch brings the two backup batteries (in different places in the car) into use and automatically opens the doors.

Chris.

 

[mneary]

And in the event of an accident an inertia switch brings the two backup batteries (in different places in the car) into use and automatically opens the doors.

Hopefully the doors would only open after the car stops moving. Opening the doors after impact but while the car is still in motion could leave you and your passengers on the street. Under the car.

 

[Hero999]

So you crash your car into a lake or river?

All the electrics will fail, and you'll drown.

 

[jimlovell777]

So you crash your car into a lake or river?

All the electrics will fail, and you'll drown.

I don't think he removed or disabled the interior door handles. Could be wrong though.

Hopefully the doors would only open after the car stops moving. Opening the doors after impact but while the car is still in motion could leave you and your passengers on the street. Under the car.

I hope he meant unlock instead of open, most modern cars automatically unlock the doors after an accident so first responders can get to you. If he did mean open, he could probably disable that behavior and should, even when wearing a seatbelt that could mean trouble. If you think about it the doors don't really need to open after an accident, only unlock. If the car is badly wrecked the door wont open anyway and if the door is able to be opened when a first responder reaches for what appears to be a door handle it should behave as before and just open.

Thanks for those suggestions,but as they're capacitive it'll need the circuitry that goes with it which I don't want to do,I need a simple on/off switch that I can put 12 volts through.

According to the datasheet the only external component needed is a capacitor. The datasheet also says the chip can be used as a drop in replacement for "most" mechanical switches. If you could rig a photo interrupt circuit to work, you could make the QTouch chip work. It has just about every quality you need, reliable, moisture resistant (especially since it would be mounted behind the door handle and you would seal the hole from the photo circuit), hidden, low power, etc...

I still think it's worth taking a serious look at.

 

[Hero999]

I don't think he removed or disabled the interior door handles. Could be wrong though.

If that's the case, it's a very dangerous idea - you should always be able to open the door manually.

 

[mneary]

If the car is badly wrecked the door wont open anyway and if the door is able to be opened when a first responder reaches for what appears to be a door handle it should behave as before and just open.

conventional mechanical door handles removed from it and replaced with an electically operated solenoid

Hence my concern.

 

[Imagewerx]

No one is going to drown and no one will end up under the wheels of my car (do all newbies here get this sort of treatment?)
When the inertia switch is triggered it starts a ten second timer before it opens the doors,when it's all finished it'll be connected to the car existing speed pulse wire and will only open the doors when it's come to a complete halt.
The original internal trigger handle inside the door still works as before,I have a small window breaking hammer next to me should all else fail and everyone in the car will be wearing a seatbelt.

NOW I'VE EXPLAINED MYSELD ALTHOUGH I'M NOT SURE WHY I HAVE TO CAN WE PLEASE NOT MENTION THIS AGAIN AND KEEP IT ON TOPIC,I HAVE DONE MY HOMEWORK VERY THOROUGHLY AND DO KNOW EXACTLY WHAT I'M DOING.

I toyed with idea of all sorts of proximity sensors including capacitive before going for the optical ones,I didn't try any as I was told they were difficult to set up and were normally over or under sensitive and never just right.

The problem I can see with that IC is that it says it won't work near a groundplane,and as the sensor board will be mounted directly to the metalwork of the doorframe,I can't see that I'll work at all? Also a quick Google doesn't seem to list a supplier in the UK?

Chris.

 

[cobra1]

what about the type of touch switch that is on the ps3?? would this work, not sure what it would be called though

 

[Imagewerx]

what about the type of touch switch that is on the ps3?? would this work, not sure what it would be called though

As I don't own one or any other type of games console I have no idea what this is? Also don't forget the aim is to keep the component count as low as possible.

Chris.

 

[jimlovell777]

The PS3 uses capacitive touch for the power and eject buttons.

Do you have access to an old remote control that can be gutted? An old keyboard perhaps? If you're lucky the keyboard would be built like this https://upload.wikimedia.org/wikipedia/commons/d/da/Inside_of_keyboard2.jpg and the switching area is very thin. I don't know how close to zero ohms they are when pressed though.

Edit: Strike that, you wouldn't have a way to connect to the traces short of conductive epoxy/glue...

 

[mneary]

I'm sorry that my concerns offended you.

(do all newbies here get this sort of treatment?)

Thank you for clarifying your experience.

More than once we've had juveniles come here with dangerous projects and we have no way of knowing.

 

[Imagewerx]

Second hand keyboards are a good idea but I'm running out oif time and don't have enough of it to go round car boot sales looking for suitable donors,hence the need to either buy new or do something that's 100% home made.
I found a name for the UK representive of Atmel who make the capacitive touch ICs,but Google doesn't throw up any details about them and they don't even seem to have a website which seems a bit odd.So does anyone know if I actually can buy small quantities of these ICs in the UK please?

Chris.

 

[Imagewerx]

I still need to know if anyone knows if a capacitive touch sensor would work if the sensor board was up against metal (the metal behind it of course)?

Chris.