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FADU F-stop Enlarger Timer App for Android
FADU F-stop Enlarger Timer App for Android
Published by Bob
20th August 2018
Default FADU F-stop Enlarger Timer App for Android


The project files for the FADU F-stop Enlarger Timer have now been moved to GitHub as that is a more appropriate place to maintain the project - but read on for an overview and release notes etc...


Current Version: 1.5.0 released to the Google Play Store.

Of note for version 1.5.0 is the ability to use Sonoff Basic R3 and Mini devices without the need to reprogram them.

Project files:


Play Store entry:

Direct link to the current live version manual:


The FADU F-Stop Enlarger Timer is an enlarger timer which can optionally drive a reprogrammed WiFi smart switch or relay module to power the enlarger's lamp on and off. It has f-stop timing adjustments for either single-exposures or exposure test-strips, including a manual-switch-friendly mode for those unable to connect the app to a WiFi enabled switch.

The app is designed to work on phones, but will run well on tablets. I suggest you always restart your phone before a session and put the phone into Aeroplane mode to prevent sluggish response by the WiFi switch as the phone needs to concentrate on talking to the WiFi and not do any of the 100 other things it can do. If it does get sluggish, toggling out and back in to Aeroplane mode seems to fix it.

Free and open source, the source code is available on GitHub ( User instructions and details of the optional hardware interface are also in the manual on GitHub and as an attachment to this article.

The timer can be used as a stand-alone timer to calculate f-stop timing for manual on/off switching of the enlarger, but can also be used to drive the enlarger lamp via a commonly available WiFi smart switch (Sonoff S20 or Sonoff Basic) that you reprogram to work with the timer. Alternately, an LC Technologies WiFi relay board module may be driven without the need to reprogramming (but as a bare pcb, it wlll need a box and a 5V power supply).

New for version 1.5.0 and above is the ability to use Sonoff Basic R3 and Mini devices without the need to reprogram them - simply put them into DIY mode and the timer app can drive them via your local WiFi router. All that is required in this case is simple DIY skills to wire them in and put them in a box.

Reprogramming the Sonoff devices requires some basic electronics knowledge, but if you have experimented with the Arduino system it should not present any difficulties. The reason for this annoying extra technical step is that I have been unable to find an off the
shelf smart socket that can be driven directly from an Android device or web page. All the smart sockets I have found have to go through a Cloud-based service and the undefined time delays caused by this round-trip makes them unusable in this application where we need to define the on/off time with precision.

If you know of a smart socket that can be driven by a web browser on your local network ***without going through the internet first*** please let me know as it would be great to avoid this reprogramming step!

The LC Tech board does not require any programming but should only be used on the low-voltage side of an enlarger's transformer/stabilizer due to poor separation on the pcb between the terminal tracks and the low-voltage circuitry.


Version 1.5.0:

1. Added [PULSE R3] mode: uses a Sonoff Basic R3 or Mini device in the "Inching" mode of the R3 DIY mode API ( to send fixed duration lamp-on commands to the Basic R3 or Mini in DIY mode. See Appendix 1 for details.

2. Added [BASIC R3] mode: uses a Sonoff Basic R3 or Mini device in DIY mode. The downside of this mode is that all the lamp-on and lamp-off signals go via your Wi-Fi router which adds random delays of typically 5 - 100ms on my network - and occasionally much more. See Appendix 1 for details.

3. Added the ability to use the camera's flash LED. Can be used for flashing paper if you add a diffuser over the LED and use the Delay setting to give you time to raise it to the right height after setting the time. Light activated relay boards do exist but keeping the bright light out of the rest of the darkroom may prove difficult. Could also be useful for testing or demo purposes.

4. Added individual volume controls for the various beeps and buzzes (scroll down the SETTINGS tab if you do not see them). A bit tricky to use due to being small (I could find no way to enlarge them in App Inventor) - I find that touching the slider button for a second before sliding it is helpful. The settings are reloaded the next time the app is launched.

5. You no longer need to use the [SET] button on the STRIPS tab. The strip's times automatically update when changing the base time or opening the tab. The [SET] button is retained although it is now believed to be redundant.

Version 1.4.0:

1. Single strip mode [SINGLE] added for when you are using individual strips of paper instead of making multiple strips across a sheet of paper. Each strip-time is for the whole f-stop calculated exposure.

2. The Memories now display their contents.

3. Now scales (mostly) correctly for tablets.

4. Main tab's F-stop Mode now reduced as all it's functionality now moved to the Strips tab.

Space was made for displaying the memory's contents by shoving the now largely obsolete f-stop calculation section on the Main tab to the right of the display.

I have updated the manual to include the changes since 1.3.0 and the instructions now include the Sonoff Basic Wi-Fi switch. I may make a reprogrammed version of this available on Tindie - TBA.

Some small tweaks:

Changed the Strips tab left side config title to "SET MODE" (still don't like it, but will have to do for now).

Changing strip Mode to [SINGLE] now updates the strip-time list - other selections already did this but adding the SINGLE mode means this button should do so too now.

Version 1.3.0:

1. STRIPS mode tab added: This mode allows the easy creation of f-stop incremented test strips. Three methods are included - see Strips Mode chapter below for details.
a. Continuous mode [CONT]: intended for users with no lamp switching hardware. Sounds a beep 0.5 seconds before the end of each strip’s time before starting the next strip time.
b. Auto mode [AUTO] : pauses the timer and switches off the lamp between each strip for a settable delay time.
c. Manual mode [MANUAL] : pauses the timer and switches off the lamp between each strip until the user taps [START] to move to the next strip.
2. Auto-Reset option added on the Settings tab. If set ON, resets the timer at the end of the exposure time to the previous time.

3. Delay time is now variable on the Settings tab from 0 to 10 seconds. An enhanced form of the previous “Count-in” setting.

4. About screen added to provide some basic info and links.

Version 1.2.0:

1. Stay Awake: Screen no longer goes to sleep (assuming your phone allows sleeping to be overridden).

2. Manual Link: added a button in the Settings menu to open this user manual on the FADU forum site using the phone’s default web browser. [obsolete in 1.3.0 – now a link to GitHub on the About screen]

3. Wi-Fi Relay Driver: Can now optionally drive an LC Technologies Wi-Fi relay module for low-voltage use. No reprograming required for this module but it should only be used on the low voltage side of a colour enlarger’s transformer/voltage stabiliser. It will also need a box and a 5V dc power supply.

4. Count-in Option: an optional 3-second delay to the count start added to allow time to prepare before the count starts. [upgraded to 0-10s selection in 1.3.0]

Version 1.1.0:

1. 1/10th Second Timing: Added ability to time in 0.1 second increments.

2. Up/Down buttons removed. Setting the exposure time is now performed by tapping the top (increment) or bottom (decrement) half of the required display number.
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Attached Files
File Type: pdf FADU Enlarger Timer Manual V1_5_0.pdf (1.39 MB, 165 views)
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