Momentary\Pushbutton Latch Switch

Another choice for protection against accidental push button switch actuation would be to install a finger guard over the switch. These come in a number of configurations as shown in the following links. One type that I would recommend is a metal cup that screws directly to the switch's threaded sleeve.

http://www.ottoexcellence.com/flip-guards.aspx

http://shopping.yahoo.com/1009767523-black-clear-plastic-push-button-switch-guard-protector/

http://www.sager.com/g13b-1906.html

For anyone who is interested in a fairly straightfoward piezoelectric approach, I discovered one successful report (using a piezoelectric pushbutton from a lighter) in the following paper from 2001 by two researchers at the MIT Media Lab (incidentally the paper is titled very similar to my Question!):

• A Compact, Wireless, Self-Powered Pushbutton Controller by J Paradiso, M Feldmeier - Ubicomp 2001: Ubiquitous Computing, 2001 - Springer

The following extract from the paper summarizes their method well:

A 4.4 μF tank capacitor integrates the charge transferred from a button strike. This, in-turn, powers a MAX666 low-dropout linear regulator, which provides a stable (although very inefficient) +3 volts supply until the tank capacitor's charge is drained. When the MAX666 is activated, the HT12E digital ID encoder is enabled, producing a repeating 12-bit serial ID broadcast via the On- Off-Keyed (OOK) transmitter module.

A drawing of their circuit:

Images of their board/components:

Here are further specific details I picked up from their implementation:

• For the piezoelectric/button section, they took the core of a Scripto “Aim 'N Flame” lighter and modified the spring action to make the strike softer.

• The piezo element generates peaks around a few thousand volts -- this is passed through a transformer, with a 90:1 turns ratio, outputting 30V at the tank capacitor.

• The conversion efficiency (mechanical to electrical) for the piezo and transformer together is 7%.

• At the point after the linear regulator, they measured 0.5 mJ to have been delivered (at 3V).

• For the wireless transmission, they used a Holtek HT-12E encoder which generates 8 bits of ID and 4 bits of data, which are in turn transmitted by an RFM HX1003 (418MHz, 7.5 mW consumption, 50 ft range).