Palm in the Darkroom




I've been using an excellent Palm program – FotoTimer – for some time. I've used it to time negative development, fixing, etc., so that I didn't have to fiddle with the cranky old timer I had. Since the FotoTimer software allows you to control hardware devices, I've always wondered whether I could make something to “hook it up” with my enlarger, to get a proper computerized (or is it “Palm-ized”?) darkroom.

I've thought about hooking up an old laptop, but finally decided for Palm-based solution, mostly because of the excellent (freeware) FotoTimer software, but also because of the size considerations: my darkroom is rather small.

After some questions to the FotoTimer author, Jan Exner, I found out how the signals are sent via the serial port (it's pins 5 and 8, signal is about 6V), and had a working idea how to make the relay. However, since the device involves 220V current, I thought I'd rather ask an expert for help than risk electrocution :-)

I managed to get some help from a friend whose electronic skills are much better than mine, and he agreed to plan the device and solder the stuff for me. I also found an appropriate housing for the parts – actually, also an old relay, used with (long ago broken) color analyzer. The picture above shows the completed device tested with a darkroom safelight.

Anyway, the relay enables me to control (switch on and off) my enlarger and the safelight via FotoTimer software on the Palm. The relay power sockets are switched: safelight (which is always “ON”) gets turned off when the enlarger is turned “ON”.

The parts were really cheap – something like an equivalent of $20 in the electronic parts shop, plus an AC/DC adapter (which I had lying around, and which I removed from its housing).

The photo below shows the parts you'll need:




The parts are:

Here is the diagram (kind of):




Don't ask me about the specifics, that's all I got. Also, I was too lazy to draw the darned thing from scratch using a proper drawing program...

Anyway, here's how the final device looks like:




Not very elegant (notice that some elements are actually glued to the housing!), but working. The printed circuit board visible inside the housing is actually the AC/DC adapter circuit board.

Here's how it looks like in my darkroom:




After a while, I realized that it would be nice if I could add a “real” foot switch, and thus be able to leave the Palm locked away while I'm handling light-sensitive material. So, I read further documentation on Palm HotSync cradle.

I found a foot switch that will do quite fine in a local music store - a cheap guitar pedal with plain on/off switch.

A bit more problematic was the fact that the pedal contacts had to be soldered directly to the HotSync cradle, but it turned out easier than it sounds.

Here's a photo of the “innards” of the cradle:




Notice a small round switch button between the two holes on the lower part of the circuit board - that's where we have to solder the contact wires.

And here's the soldered result:




I can now start/stop the enlarging process using the foot switch.

The whole apparatus finally looks like this:




In short, I found that Palm Pilot is actually a rather handy gadget for photographic purposes – I also use it in the field to take notes of the shots I take (exposure, f-stop, motive, etc.). There are several useful Palm programs for photographers – check out the usual sites, try this site with various tools or check out this survey.

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