5. Build the developing tank warmer.
Paterson developing tanks are cylindrical,
so instead of making a holder out of sheet
metal, I used an old cigar can that fit it nicely
(Figure I). A large soup can also works.
I drilled a hole in each side of the tin and fitted a Nichrome coil in place with fire cement
as I’d done with the bottle warmer.
Finally, I glued the temperature sensor to
the tin with epoxy resin. This heater coil is controlled by a transistor connected to Arduino
pin D7 and the sensor feeds into pin A4.
6. Make the case.
The laser-cut Photo Lab case was manufactured from birch-faced plywood by my
friends over at Hines Design Labs. I designed
the case to accept an ATX power supply, and
before I fitted it in, I covered the air intake
with wire mesh (Figure J). You can see my
7. Final assembly.
I connected several of the power supply’s 5V
(red) lines together so they could handle the
current for the heater elements. The power
switch for the PSU acts as the power switch
for the Photo Lab, and I connected the green
and black ATX wires together so that the PSU
supplies power as soon as it’s plugged in and
I fit the aluminum box and cigar can into
the project box using a combination of wooden blocks, Meccano brackets, wood screws,
and wood glue.
Nothing inside the box should get hotter
than 140°F ( 60°C), so I didn’t make any
special effort to protect the wood. As a final
measure, I packed some fiberglass thermal
insulation around the heaters.
involves no modifications beyond exchanging
the transistors for solid-state relays.
The timer and auto agitator take all the
stress out of processing film, and mean that
I don’t have to keep an eye on the clock. I can
leave the film to process and trust that the
tank will be stirred every few seconds.
The processor is also handy for developing
black and white film using weak solutions to
achieve finer grain, which is a slow process.
Experimental developers such as caffeine
(yes, caffeine!) can take more than half an
hour to process, and my Photo Lab machine
lets me avoid a nasty hand cramp from manually stirring a tank for 30 minutes. ;
Download the Arduino code, schematic
diagram, and Arduino connection table at
makeprojects.com/v/31, where you’ll also find
the optional box cutting templates, panel artwork by John Ranford, and pushbutton PCB
Andrew Lewis is a keen artificer and research scientist
working in archaeometrics and complexity science at the
University of Birmington. He is a relentless tinkerer, whose
love of science and technology is second only to his love of
The Big Picture
I’m very pleased with this project, and I now
use it to process my rolls of film. The only
problem so far is that the heaters take a long
time to bring the bottles up to temperature, so
I think I might replace the elements with 12V or
240V versions. This should be easy because it
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