My first enlarger timer was a Gralab--you know, the one with the minute and second hands. The last second on it isn't very accurate.

Then I got ahold of a Gralab 505 electronic timer, with buttons and switches. It worked OK, but I had to avoid using a couple of the switches because they were dirty and weren't reliable. It was also a little quirky to use. These are both standard/linear timers.

Then I heard about the FADU f/stop timer app. I've heard about working with an f/stop timer, which calculates test strips and adjusts single exposures using f/stop increments instead of linear timing. Where it shines is doing test strips. I used to do them a fixed number of seconds apart, for example, 5, 10, 15, 20, 25 seconds, but the lower numbers are a one stop jump and they get smaller as you go up. The app alone can calculate the timing for different increments of f/stops, which is helpful in itself if you set your timer manually, but I was curious about getting the smartphone to control a wifi relay as per the description in the app store.

I had an old smartphone with an OLED display (apparently better than a backlit display because it puts out pure red, with no green backlighting bleeding through), so decided to try putting together a wifi relay for it. $15 worth of parts later (1 LC tech wifi relay board, 1 5v power supply, 1 electrical outlet, 1 outlet cover, 1 switch, 1 outlet box) and a bit of soldering and I got a pretty sweet f/stop timer setup. I turned down the display on my smartphone to minimum, uninstalled any extraneous apps, turned off all notifications, and tested the red display of the app by putting it upside down against a piece of photographic paper for 30 seconds, with no exposure of the paper, so the OLED display works great displaying a red that the paper is insensitive to.

The wifi relay even has a normally closed switch so I connected that to the safe light outlet, and the enlarger connects to the normally open part of the relay. The timer is interesting. I normally do test strips 1/3 stop apart, but if I need a rough idea, I can set it to 1 stop apart. It seems to be able to time split seconds, so I've taken to shorter exposures since the timer will do it accurately. You can compensate for any latency in the wifi signal/relay if you want, but I haven't found the need. I've included a pic of the setup below (the smartphone display is brightened for dramatic effect).

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I'm pretty happy with the setup because: It only cost $15 (and makes use of an old smartphone), it's small, and it gives me f/stop timing capability. I can provide more details on assembly if requested.