Subminiature Electronic Flash

The following are some notes about how I used parts from a disposable camera to assemble a subminiature electronic flash for my Minolta 16-II.

The guide number of this flash is pretty low. I haven't done careful tests, but the results I'm getting are consistent with a guide number in the neighborhood of 25 at EI 100 or 50 at EI 400. For example, this flash seems to give pretty good fill at about five feet using XP-2 400 at f/11; but I'm relying on memory for the f stops I was using.


Here are some illustrated construction highlights.


DANGER! The capacitor in an electronic flash contains high voltage long after power is removed, even after the flash is fired! Failure to drain the capacitor could lead to injury or even death!

Remove the battery first, then pop off the camera's front cover. Do NOT touch the circuitry inside until you have shorted the leads of the capacitor with a small plastic-handled screwdriver, as shown in the picture. (This capacitor is small enough not to damage the screwdriver blade.) To make sure the capacitor is fully drained, hold the blade securely against both leads for several seconds after the initial spark.

If you ever apply power to the circuit, be sure to short the capacitor again before handling the device.



This picture shows a diode and two resistors that have been relocated to make room before trimming the board with a cutoff wheel. This is when it's handy to have a second camera to refer to, as you reproduce the trimmed paths with haywire.



This picture shows the flash components tack-glued (with a low-temperature glue gun) to a piece of thin plywood. This kept the components together in their final arrangement while I finished wiring and testing the circuit.

Remember that, once powered, the circuit stays "hot" until you remove the battery and short the capacitor!



Here's the final assembly; potted in epoxy filler, shaped, and painted.

DANGER! Be very careful as you sand the filler into shape. It is easy to sand through to components, possibly damaging the circuit, and almost certainly leaving dangerous voltages exposed. After I finished sanding, I had to recoat part of my flash with epoxy to seal a couple of nearly invisible hot spots.

BTW: You can see the charge status blinker in this shot. It shines through the glass/epoxy filler pretty easily, so I just sanded a "window" in the paint. Then I sprayed that corner with the lightest possible dusting coat; so it looks black, but is still transparent enough for the light to show through.



Here's a look at the bottom. I molded in the strap when I potted the circuit, but I wish that instead I had molded a channel for it and glued it in later. It got messed up some as I sanded and painted (also it could be a bit longer), so I might decide to remove it later and glue on a new one.

The ridge near the end of the flash rests against the end of the camera to keep the flash from slipping around. I'll probably also add a ridge along the front edge for the same purpose. The bottom is covered with flocked paper (from Edmund Scientific) to avoid scuffing the camera.


That's all for now!

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Marcus Brooks — 4 April 2000