this is my simple weight switch controlled flash unit used to produce this imageSwitch: the switch is simple ... it consists of aluminum tape a peace of metal 2 nuts and bolts a peace of 1/4th inch acrylic a 1/4th inch bolt (for tripod mount) the switch is sensitive depending on where you put the load ... its a normally open switchControl Unit: the control unit is a triggered by as little as 2 volts or as high as 40 volts (3.3-12v recommended) via a resistor and a transistor ... (the 10K that carry's to ground is a pull down resistor to prevent misfire from radiant voltage ... higher resistance here can give you lower input voltage lower resistance gives you higher voltages in but the 10K feed resistor must remain at 10K) that triggers a 220V 5A relay via a 1A highspeed diode that prevents inductive feedback current from being jammed in to my transistor than the relay triggers the 400V 1MA line that the flash uses to trigger and i can adjust inverting ro non inverting via a switch that selects witch side of the relay to use (NC or NO)there are 2 ways of doing this1) Relay ... Pros. simple bidirectional triggering and i can select inverting or non-inverting without drawing any power ... Cons. non-solid-state so it will degrade with use (but at only 1MA it can last years) with a large bump it can trigger prematurely ... it draws large amounts of current while being triggered and there is a small delay (i have yet to be able to measure it)2) SCR (silicon controlled rectifier) ... Pros. Fast, Reliable, Highspeed, Draws little current, SolidState ... Cons. Expensive, Hard to find, Omni-Directional (you have to match positive to negative) you need to use an logic inverter that draws current to invert, gets hot (maybe not in this setup) and you need to use the ground of the HV supply as the ground of the circut so if something goes wrong you have 400V flowing threw your projectFlash:1) a modified disposable camera with the battery replaced by a plug (connected via wire to a 1.5V Dcell for prolonged use) and a 3.5mm pone jack to trigger the flash parallel to a N.O. button for triggering ... Pros: Fast, Simple, constant output ... Cons. Nonadjustable, hard to point and has a limited range2) an nikon SB-600 flash on a DIY remote hotshoe [link] ... Pros. Simple to point, has zoom settings, fully adjustable output, can trigger many times a second and easy rechargeable batteries ... Cons. produces a delay of about 5MS or so and more of a pain to set upuse: the control box is set on inverting i place a standoff between whats going to be captured and the switch i place the flash on the camera and i hit it ... the delay can be controlled with simple leverage ... depending on ware i place the standoff on the switch the standoff leaves the switch at different times ... it requires a gut feeling to get it JUSTTTTT right... put your camera on an exposure of a few seconds ( i use my intravolomitor to delay 20 seconds than do a 3 second exposure) cut off all the lights and let the flash capture the momenti can trigger this with my laser trigger also [link] EDIT 8/11/2010: i got a hackaday feature! [link] to any one looking to make this let me explain how i made the flash unit in detailwhen you open a disposable camera with a flash DONT TOUCH THE CIRCUIT BOARD locate the primary capacitor and short it out with a screw driver to empty the load (the last thing you want is to get a 200V shock) find 2 little peaces of metal that hang out of the side remove them and solder in the trigger wires (or wire them to a phone jack so you can exchange them)OPTIONAL: find the charge button and attach a switch for easier charge and remove the battery and attach a power socket and externally make a battery pack or power source with a 1.5V battery (D cell recommended for extended use but do not exceed 2V)