Arduino based timer for enlarger used in analog photography

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Analog photography is a fascinating area of art, combining creativity with interesting chemical processes. Staple of doing analog work the way it is meant to be done is printing of your work. Enlarger is a device that projects light through a negative onto a surface on which photosensitive paper is to be placed. Nowdays, old enlargers can be picked up for quite cheap, but they almost universally lack one thing- the timer. Yes you can flick on a switch, use stopwatch and turn it off, but timers can provide more control over the whole process. And since they are quite expensive, making your own is logical way forward.

I currently work on a prototype of Arduino controlled relay for that exact purpose. It is very simple circuit and code.

This project offers cheap alternative to usually expensove vintage (or new) darkroom timers. Uses just a handful of components

x-arduino - 1.57 kB - 06/10/2020 at 18:20


  • 1 × Arduino Nano
  • 1 × AC relay with Arduino control
  • 6 × LED diode
  • 6 × 220 Ohm resistor
  • 2 × 10 kOhm resistor

View all 6 components

  • It's alive!

    lazar.zenit06/10/2020 at 18:51 0 comments

    Finally bought all of the components and put this together. Also code is updated and so is the github page. More pictures in instructions section.

  • Code cleaned

    lazar.zenit04/06/2020 at 19:11 0 comments

    Added cleaner code with captions.

  • Prototype finished

    lazar.zenit03/29/2020 at 12:17 0 comments

    Now has functions of single button time changing in seconds, displayed on 6 LED in binary (didn't have 2 7-seg displays, but looks cooler none the less). One button executes, and one is for reset. Red LED in picture acts as relay until it ships.

View all 3 project logs

  • 1
    Study the circuit diagram
  • 2
    Gather the components

    Buy all the components from the list and arrange them in aesthetically pleasing manner

  • 3
    Make all necessary opening on the box and on the pannel

    Be smarter than me, use something better than drill, sandpaper and file. Fit you switches and LEDs

View all 5 instructions

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Ken Yap wrote 06/11/2020 at 22:00 point

Cool, brings back memories of working with photographic chemicals as a kid. I built a vacuum tube timer wuth a variable R, C, and a neon bulb as the trigger element in those days. Also a CdS cell exposure meter for estimating paper exposure.

One thing, are yellow LEDs safe for photographic paper? I remember darkroom lights had to be red.

  Are you sure? yes | no

lazar.zenit wrote 06/13/2020 at 08:04 point

Wow I bet that looked awesome! That sounds pretty high tech compared to this. Yellow LEDs are not that safe, but they are quite weak here and not in direct contact. To be honest I use red LED bike light as my safe light and it works good. Only when I'm impatient and shine it directly to paper form up close does clouding occurs.

  Are you sure? yes | no

Ken Yap wrote 06/13/2020 at 08:25 point

I suppose the spectrum of LEDs is narrower and may not have significant energy in the wavelengths the paper is sensitve to.

Yeah, I used an old amplifier case for the timer, and the knob was for time instead of volume. The relay was an old telephone exchange relay. The vacuum tube was an octal base tube salvaged from an old radio. I was so happy to be able to recycle those old components. Of course in those days I never thought of taking a picture (film cost money) for posting to Hackaday in the future, hahaha.

Happy hacking!

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