Posted August 29, 2015
The Dangerpants Labs Darktimer is a simple-to-build Arduino-based project, which provides up to 100 individually programmable sequential timers, detailed audio feedback, and which generates no light. It was designed with darkroom use in mind, although it is adaptable to many different tasks.
Because it was designed for darkroom use while developing film, its design concentrates on making it very useable in complete darkness: multiple timers can be run in order with a simple button press; audio tones sound once a second, with a double-beep that can be configured every N seconds, a longer beep on one-minute boundaries, and triple-beeps for the final 5 seconds alert to the timer being nearly done.
Construction is based around an Arduino Pro Mini, with a handful of switches, a speaker, an LCD, and a battery rounding out the required components (see the Bill of Materials for details). It is suitable as an early electronics project, but does require soldering and case fabrication to make a finished timer suitable for darkroom use.
The Dangerpants Labs Darktimer, including source code, schematic, and documentation is licensed under the Creative Commons BY-NC-SA 4.0 license. It is intended to be free for anyone to use for any non-commercial purpose they see fit, pursuant to the disclaimer. Please credit Ian Johnston or Dangerpants Labs.
The Dangerpants Labs Darktimer by Ian Johnston is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.
First Full Prototype Finished December 18, 2015
With the installation of the firmware into the Arduino Pro Mini, the Darktimer v1.0 final prototype was finished last night. The code appears to be working perfectly, though the interface was not intuitively obvious to coworkers today so there may be work to do there.
I'm pleased to say that v1.0 of the Darktimer is done. I have some work to do on documentation (noticed the Fritzing diagram in the construction guide is missing at least one wire to the LCD), but things are looking good!
Close to done! September 24, 2015
The documentation is nearly done. Most of the writing is finished, and what remains is a bit of photography to replace the placeholder ADI photos, and a wiring diagram for the construction guide.
Once the documentation is done and the final v1.0 code is uploaded, I'll update the hackaday.io project with the URL.
In prospective-feature news: I will be looking into using sleep modes and some hardware power management to get the power consumption down. A commenter on largeformatphotography.info also asked if I would make the timer temperature-compensated, which sounds like an ideal v1.5 feature. The idea is that you drop a temperature probe in your developer bath, and modify the time of certain timers based on the temperature's difference from a setpoint (usually 68°F or 20° C) by a given ratio.
Working on documentation August 29, 2015
The code is essentially done, for version 1. I'm working now on preparing the documentation to make it a publishable project.
Bill of Materials - A list of parts necessary to build the Darktimer
Construction Guide - Information on building your own Darktimer
User's Guide - This document describes how to use the Darktimer once it's been constructed
Specifications - The Darktimer's physical and software specifications
Dangerpants Labs Darktimer Disclaimer
The Dangerpants Labs Darktimer is not a precision timer. It is not guaranteed to be free from bugs, including bugs which may prevent it from counting down time correctly or accurately. Test your Darktimer to your satisfaction before using it in the measurement of any events that matter. Do not use the Darktimer for any purpose which may put human life at risk.
Dangerpants Labs assumes no responsibility for any use of the Darktimer, and makes no guarantees of its suitability for any particular purpose. Dangerpants Labs disclaims all liability for any use of the Darktimer.
Your use of the Darktimer is entirely at your own risk. No finished devices are available for sale. Building your own Darktimer is express consent to the terms of this disclaimer.