Bells and G Forces

A "one-shot" is a device that generates a single pulse when triggered. There are many circuits, but the simplest way to generate a pulse when a switch closes is to put a capacitor in series with the load. The combination draws a pulse of current, then looks like an open circuit once the capacitor is fully charged. If the load is the coil of a small relay, you can drive a bigger load without needing an inconveniently large capacitor. You will need some path for the capacitor to discharge through when the switch opens, such as a parallel resistor.

A gadget that measures acceleration is called an accelerometer. Tiny solid-state ones are made, but I haven't looked up the prices lately. If you don't need accurate calibration, it's fun to experiment with homebrew approaches, such as a mass on as spring with some way to measure the deflection, or a phonograph cartridge (Do they still make cheap ones? It might be easier to buy an old turntable at a thrift store.) with a small mass attached to the stylus, or maybe a U-tube with colored water and an optical liquid-level detector. The acceleration you mention is about half a gee, so you don't need great sensitivity.

If you are just experimenting, and don't need small size, you might want to try a speaker as the mass-on-a-spring sensor. You will need to attach the desired (non-ferrous) mass to the center of the cone. Measure the response from the speaker terminals. This system will measure acceleration along the axis of the speaker; the speaker suspension prevents motion in other directions.

Best regards,

Bob Masta D A Q A R T A Data AcQuisition And Real-Time Analysis

The switch doesn't move and is not mounted on the door.

Space the switch off the door frame so that the magnet PASSES it. Use normally open contacts or invert the state.

Accelerometer

Have a look at some of the datasheets and see what you think. I think that in the simplest form they just produce a voltage proportional to acceleration. Others give out pulses with different duty cycle proportional to acceleration.

Analog Devices make small accelerometers,

Freescale have a range of similar devices