Darkrook timer and safelight

I had to order some cheap red LED strips from Amazon, and it's surprisingly hard to find plain and simple 5v ones.  These arrived, and I added 2N3904 NPN transistor to drive them.

Coding it was fairly easy actually.  I used the blinkWithNoDelays() sketch as a starting point, and just ran through checking inputs and timers based on millis().

A quirk is that you can't press down multiple timer buttons, or the timer start button, or enlarger button reliably because they are all in a voltage divider together. However, there's no need to press these buttons together, so that's not a problem.

One feature is that it saves the timers in the EEPROM, which means that they persist when the timer is switched off.  Another feature is that I convert seconds to MM:SS time, which is more readable for minutes.  There isn't a colon on my display to mark this, but I can live with that.

The whole code is in this gist: https://gist.github.com/MarcelloTheArcane/7be865507c2018faa79d0f57276a63ac.

The tone() library says not. Well, the Neopixel library says no to the tone() library.

A shame really, since I had some spare Neopixels kicking around. Originally I planned to use them, but it looks like I'll have to find some cheap red LEDs instead, and drive them with a transistor.

So, I finished my (rat's nest) wiring, and there doesn't appear to be any short circuits when I turn it on.

One small change - I wired all the momentary push buttons (4 timer switches, enlarger switch, and encoder switch) together in a voltage divider. When I tested it on the Serial Monitor, the values were all distinguishable which is great. All the resistors are the same 4.7k ones, so that's easy. Some tutorials online had different resistor values, probably to make sure the increments are linear rather than logarithmic.

The Uno I am using is a clone because I'm cheap, but it also has a very handy feature where the pins have solderable holes next to the female connectors, so I used them. I also had to desolder one segment of the connectors in order to squash everything in.

Next step is to start programming in earnest, the display is going to take a bit of thinking about because in the end I just soldered the anode wires to any old pin on the Arduino.

It turns out the display from The Pi Hut was faulty, so I returned it for a new one. I also screwed up the illuminated red push switch by blowing the LED inside (idiot!), so I needed a new one of those too.

I'm soldering wires to various buttons and switches, and the main issue at the moment is making sure I don't glue or fix anything too soon.

I bought this seven segment display from The Pi Hut. There is a reason, as well as just being cheap.

It's red, which is good for B&W paper (there will be an option for zero display output however). It also has four decimal point lights, rather than a clock-style colon. I'm going to use this as an indicator for which timer is currently active (there will be four), so I can preset enlarger, dev, stop, and fix timers.

It's common cathode, which means it doesn't work with the advertised TPIC6B595 (I think I read it wrong). Thankfully though, Arduinos have just enough pins to allow me to operate all the periphery.

Unfortunately, the fourth digit was being weird, so I need to look at that. Maybe I wired something wrong.

Meanwhile, I got the relay clicking (small wins) and managed to read the rotary encoder. The red backlit safelight button I plan to use has got a nice dim red, so that is great.

I got some initial plans drawn up for the body in Onshape (my CAD program of choice) and I have some black filament on the 3d printer.

My only challenge now is how I am going to output wires for the LED strips - I think a stereo audio jack would work.  I also need to think about how removable it needs to be, with the 240 volt connection.

I am making an integrated safelight/timer console, which will have a countdown timer with three preset timer options, and an enlarger switch for controlling that when I need to.

Neopixels? Overkill? Mais oui! But I have some left over from an old project, so I may as well use them for something.

I'm envisaging quite a custom light setup, with some lights underneath the worktop as well as along the back edge. You generally need to keep them low and dim around paper, despite its orthocromaticity.

I've bought bits from The Pi Hut, so hopefully that's all I need. So far the total is around £30.