Category Archives: darkroom

Darkroom Timer – Full Details

Darkroom Timer Schematics JPGHere is a list of everything you need to build the Timer:

Parts you will need:

1 x Arduino Uno or compatible Board
1 x 5V Power supply
1 x 12V Power supply
1 x Breadboard or compatible routing board
6 x 40-50k Resistors
6 x Generic Diodes
2 x Dual input OR 3 x single input Relays(12v trigger, 240v current or 120v or whatever your country has)
3 x 7 Segment Common Cathode RED LED Display Modules
3 x 4511 7 Segment Latch Enabled Drivers
3 x Generic NPN Transistors
1 x Manual Flick Switch
5 x Push-button Switches
1 x Enclosure, I used a plastic box used in outdoor alarm boxes(you can get these at any electronics/hardware store)
1 x Female Jug Plug
1 x 240v/120v Female Socket

Here is a bit of a layout guide:


DIY Darkroom Enlarger Timer



I have been using a very old, most likely 10th hand,  enlarger timer for many years now. Its a very simple design…It has a manual rotary dial, you set a time in seconds, or multiples of 10 seconds, and slam down as hard as you canon the START button…90% of the time it works..The other 10% of the time the wound spring slips and it exposes my paper for a very brief instant… I’m getting sick of this..Also I’m getting sick of not being able to find good digital timers that don’t cost hundreds of dollars…so I’m making my own!

Some might say my design is overly complicated. I’m using a small Arduino Uno board to control 2 physical relays. I know there is a simpler way of doing this but I will stick with what I’m good at.  I have 3 red 7 segment LED Displays, some push-buttons for adjusting the time etc..I was also going to make my own display driver but I have since found the 74LS47 chip that will make this whole thing really simple. So fat i have spend $150 on all the parts…i think it should take me a few hours to put together and test…hopefully I don’t blow up my darkroom