This is a rough guide to making a sip/puff switch operate standard switch equipment.
Sip/puff switches (also known as low pressure/vacuum or suck/puff switches) can be obtained from www.rswww.com for around £23 each with 1m of PVC tube (code 317-443). You attach a tube to the front or the back of the switch (in the middle), to give control via either sip to activate, or puff to activate. They are in effect, simple on/off switches, and require no external power. To get both actions using one tube, you will need to mount two switches one on top of the other. Update: An alternative worth looking at is the Herga Differential Pressure Sensor. Link via Gavin Tan at SpecialEffect.
If you're an absolute beginner, we strongly recommend that you follow "The Basic Soldering Guide" - by Alan Winstanley.
"Pneumatic switches which are vented both sides of a diaphragm and can thus be used in either pressure, vacuum or differential modes. The single pole contacts remain in the normally open position until the operational differential pressure is reached. As the contact pressure is dependent on the air pressure, the switch rating will be reduced when used at the minimum operating pressures."
Connect your speaker wire from the 3.5mm plug to the sip/puff switch.
Connect an appropriate length of PVC tube to the switch and test.
Find a way to position the switch near to the person's mouth safely. Try to keep your wiring as tidy as possible.
Image pictured is of Mark Bosanquet-Bryant's sip/puff Playstation controller.
D.I.Y. Text PUBLIC DOMAIN 2003 - www.OneSwitch.org.uk