Wiring the Enlarger Lamp
This is the simpler part of the project though one should only attempt this if you are confident with mains wiring. I arranged everything inside a pattress box from the local DIY shop. I used a household switch mounted on the box as a manual bypass for the enlarger lamp so I could use the enlarger while I finished the software. The schematic is shown below.
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| Enlarger lamp control schematic |
I used a terminal strip to make all the connections Where two wires go into one side of a terminal I would solder these together as it makes it easier to manage. The terminal strip passes the mains ground and neutral signals through while the live signal is connected to the normally open (NO) contacts on the relay. The light switch mounted on the pattress box is connected across the relay contacts so the lamp can still be turned on manually if the Arduino is not working or connected. The relay is controlled by the Arduino GPIO (General Purpose Input Output pins) configured as an output. Three wires make up this connection as the Arduino board supplies power (5 volts) ground and the signal to control the relay.I also installed in the pattress box the 5 volt power supply for the Arduino. In this case I bought a cheap USB phone charger that supplies 5V at 1A and removed the circuit board. The mains connection I connected to the terminal strip mains wires I then used a USB cable to connect the charger board to the Arduino routed through a hole in the pattress box.The photo below shows how it all fits together.
Making the Filter Wheel
As mentioned previously the filter while simple has some design challenges. The first issue was what size to use for the filters. Normally I use the above-the-condenser filter tray on my Meopta enlarger. Since the enlarger has a red safe filter that swings under the lens I would use this for the size. This works out to be about 55mm. Since I am driving this from a servo that only has a 0-180 degree range this sets the size of the wheel. This makes it roughly 230mm diameter. Since half the wheel cannot be used I basically cut it in half. I then need to make it lightweight but it still needs to be stiff. I made the prototype out of cardboard with some thin plastic as a stiffener glued to the hub and as an attachment point for the servo. Since it is a half circle (vs a full circle) this saves on rotational inertia but means of course it is off balance. As I use it I will evaluate this choice. If I like the arrangement I plan to later commit the wheel to machined aluminium.
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| Filter Wheel |
Mounting the Filter Wheel and Flash LEDs to the Enlarger
This is easily the most challenging part of the project. My Meopta enlarger does not lend itself to adding on home made devices. There is a single threaded hole for mounting the red safe filter. I built a quick bracket based on this but will need to drill a new hole to make it permanent. This allows me to at least check the dimensions and make final adjustments. It is a bit Heath Robinson/Rube Goldberg but hopefully should work.
Wiring the Filter Wheel and Flash LED
The photo below shows the underside of this bracket where I placed all the electrical parts and connections. I used an old Ethernet cable for the 8 wires of which six are needed so far. The LEDs still need to have a diffusion cover fitted over the top to ensure uniform light on the paper. I still need to test this setup and I have concerns about the ability to get a uniform light coverage on the paper. Even though the LEDs are white they likely have a spectrum that is not continuous like an incandescent source so how it acts on VC paper remains to be explored. The brightness of the LEDs can be controlled in SW in case they are too bright.
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| Underside of Enlarger bracket |
Again I used a terminal strip for the connections and screwed the various parts to the wood. Once mounted this underside it is not visible during use. The following is a schematic view of the same thing.
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| Enlarger bracket schematic |
(To be Continued.)
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