This project started a while ago for me (probably back in July 09), when I got my first Vivitar 285HV flash.

By default, this flash has 4 manual power settings. Full, 1/2, 1/4 and 1/16.
I never liked the fact that there was no 1/8 power. So searching the web I came across some DIY projects to add a selector knob to select different power settings.

From what I remember (will update this later) they were all too intrusive,and modified the flash body too much for my liking.

So after poking around a bit, and taking the unit apart a few times, I decided to make my own flash power selector.

The 285HV has a module that plugs into the front of the flash. My idea was to replace the circuit board inside this selector, and use all the positions of the selector to switch between different power settings.

I have created a schematic and board layout (In Eagle board design software) of the circuit board that’s inside the module.

This will allow me choose between 8 power settings. Full, 1/2, 1/4, 1/8, 1/16, 1/32, 1/64 and 1/128. The module has 8 positions, so I figured I’d use them all.

The way the front module/selector currently works is by making an electrical contact between the center metallic circular pad and the 8 outter pads. When you turn the knob it completes the circuit between the two green dots (that’s where the 2 wires leading back to the camera connect to)  by placing a different resistor in the path of the circuit, or keeping the circuit open for full power.

The resistors used are tiny surface mount resistors (package 0603)

The resistor values for the corresponding power settings are as follows: 100k
Full power = No resistor
1/2 power = 180k
1/4 power = 82k
1/8 power = 46k
1/16 power = 24k
1/32 power = 12k
1/64 power = 6.8k
1/128 power = 4.1k

These values were taken from the “Ultimate2 Vivitar 285 Flash Mod” strobist thread on Flikr. Thanks Benjamin!

Today I have just produced my first prototype circuit board.

All the resistors are surface mount, to keep the size down (there’s not much space in there for much circuitry.

I will do a trial fit tonight and adjust the design accordingly.

This post will be updated until I get a working design.

When I get the details sorted out, I plan on making these circuit boards available to anyone that wants one (for a few bucks)

Leave me a comment with your thoughts/suggestions.

UPDATE: 26 June 2010

Made another board which I was hoping would have fixed the issues I had. No luck.

The issues I was trying to fix was that the selector didn’t always “select” the correct resistance. I was attempting to copy the pcb layout of the pads inside the selector, but even my second design still has a couple of settings where the selector bridges two pads.

Will have to do some more research.

UPDATE: 12April2010

Soldered up a board with all the resistors. Attached it to the 285HV, and fired off some pictures. Will post some images (of a white wall) at all the intensities.
There seems to be some problems with a few of the settings, but most look like they work pretty good. I will need to do some more fine tuning of the design before I release this to the public.

This work will be posted as open source, and I will also sell fully populated boards to whomever wants to buy them if they can’t manufacture their own boards, and solder their own components. I will also retrofit the board to your existing power module, but you have to ship it to me first.

So let me know if you’re interested in buying one.

UPDATE: 28 March 2011

Project is on hold.
Currently working on getting PCB/milling capabilities at home, to start this project again.