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Make a force sensitive resistor (a pressure sensor) with spare parts instead of spending $5 - $20 each.
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Signing UpStep 1Materials
Tools
- Soldering iron
- Hot glue gun
- Knife/razor
- Wire cutter
Components
- Solder
- Hot glue
- One-sided copper PCB
- Conductive foam
- Wire
The foam
Conductive foam is what microcontrollers generally come packaged in. If you've received little ATmega microcontrollers or PICs, sometimes they'll be surrounded by conductive foam inside a little case or box. Not all conductive foam is created equal: some of it bounces back into shape faster than others. If you use PIC foam to make your FSR, it will respond quickly, but if you use ATmega foam will take a second to release. The fact that this FSR has a visible deformation is the primary difference from other FSRs.| « Previous Step | Download PDFView All Steps | Next Step » |
Be sure to check out Hannah's work too: http://www.instructables.com/member/Plusea/ She does a ton with resistive material, and has some links to suppliers.
Or, c = 1 / (f x r). So if you want a 500 Hz wave and have a 1 kiloohm resistor, you need a 2 microfarad cap.
I'm guessing a keyboard circuit wouldn't be very useful for making a matrix of these; but I haven't really dissected enough keyboards, so don't let me dissuade you :)
As for the HowStuffWorks article I'll comment on some strange ideas in it, after quoting it.
http://computer.howstuffworks.com/keyboard3.htm
"Metal contact and foam element keyboards are increasingly less common. ...
Both technologies have good tactile response, make satisfyingly audible "clicks," and are inexpensive to produce. The problem is that the contacts tend to wear out or corrode faster than on keyboards that use other technologies. Also, there is no barrier that prevents dust or liquids from coming in direct contact with the circuitry of the key matrix."
Foam element keyboards never were common, and are rare as hen's teeth these days. I'm wondering if the author really mean silicone dome element switches, the type used in things like some landline cordless phones and cheaper TV remote controls where there is a black round bump on the back which is embedded with conductive material. That type weren't all that rare, I think today's all rubber roll-up types of keyboards still use that design but I could be wrong.
Both are not inexpensive to produce. Relatively speaking the common rubber dome type found today is the inexpensive one, while metal contact (mechanical switches of one type or another) are by far the more expensive type of what were once far more common than they are today.
The contacts on metal element do not tend to wear out or corrode faster, on the contrary a decent metal element (mechanical switching) keyboard tends to last over 5X as long as today's rubber dome plus deposited film circuit types do.
You can't spill anything on most of today's rubber dome keyboards either because the liquid simply goes to the edge of the rubber dome mat where it then gets inbetween the two sheets of film, and because it is a depositing layer it is very thin and unlike the old fashioned copper-on-PCBs, small current shorts from liquid can degrade or even burn through the traces. I've lost several rubber dome keyboards like that, they can be opened and cleaned out but once that trace is gone it's very hard to repair. I've tried attaching a wire with rear window defogger repair solution and a conductive silver pen. The defogger flaked off and was too thick, the silver pen worked but later failed again.
The funny thing is that even in the picture that article provided, you can see the deposited traces in the rubber dome picture are very degraded where they are discolored at the bottom. That particular keyboard they opened had probably failed or became very flaky already and that's why it was chosen to be taken apart. Rubber dome keyboards take less effort to press and are the cheapest to make, that is why they are the most popular (except buckling spring types on laptops due to being shorter to allow for a thinner laptop).