Reduced To A Single Tap

(This is not a post about plumbing.) 😀

It’s been a while since I last wrote about personal automation. And in Stickiness I talked about what makes automations stick for me.

This post is about experiments with RFID detection and automation. These actually turned into something I use daily when I’m at home.

Hobbyist Digital Electronics

Let me digress a little. When I was young I learnt all about Kirchoff’s Laws and other aspects of analogue electr(on)ics. But my real love was for digital electronics. I messed around with Zilog Z80 microprocessors and the various support chips. Indeed these were the core of part of my Masters in Information Technology. And this is where I learnt my first assembly language – but not my last.

But then the rest of my life took over. 😕😀

Digital Electronics In The 2020’s

A few years ago I got into Raspberry Pi computers – mostly on the basis they were cheap Linux machines. This helped a bit with trying things out on Mac as well, with many of the utilities being essentially the same. And I did a little electronics – but not much.

But then last Xmas I acquired a Pi Hut Maker Advent Calendar. As the name suggests, it contains 12 experiments, which mostly build on each other.

At its heart is a Raspberry Pi Pico – which has a runtime rather than a Linux operating system. You program it from a real computer, which might be a Raspberry Pi. I’ve done it with a Pi but generally use one of my Macs.

The runtime interprets one of two flavours of Python: MicroPython and Circuit Python. Generally I use the former – as that is what the Advent Calendar introduced me to – but there have been Pico-based devices where Circuit Python is easier.

Pico W Is A Game Changer

The Pico comes in two flavours:

• The Original Pico
• The Pico W

The latter has Wi-Fi (and Bluetooth). Wi-Fi opens up lots of Automation opportunities.

While you could use the Pico to automate via a USB connection, Wi-Fi is much more flexible.

I have automations using two mechanisms that require REST interactions:

• On the Mac with Keyboard Maestro.
• On an iOS device with PushCut.

As Mac and iOS devices have different capabilities it made sense to learn how to work with both.

A Single Tap?

One of the devices a Pico – of either variety – can drive is a RFID reader.

It’s not difficult to write MicroPython code to handle card taps on the reader. Essentially you’re in a wait loop until a tap is registered. Then you “do the thing”.

My code uses the identifier embedded in the card to index into an array. Based on that a specific automation is kicked off – via a URL scheme. (Either Keyboard Maestro’s or Pushcuts’s.)

While a card can carry more information they all have a 4-byte identifier. Which is how uniqueness is supported.

My code writes a message to the (Thonny) console if the card has an identifier that is not handled. That way I can add the card to the array, along with an automation routine.

Experiments With RFID Cards

While RFID readers often come with visibly blank cards and keyrings, I’ve experimented with other RFID cards (or what I thought were):

• Supposedly many credit cards have RFID built in. I wouldn’t recommend using these as some idiot might run off with them – even if you stick to expired ones.
• We went on a cruise recently – and the on board passes got harvested as RFID cards. (They were no use for anything else after the cruise, except perhaps for nostalgia.)
• I discovered my Gautrain card (cancelled since I hadn’t been to South Africa in years) also works.
• I wondered how a Philips Sonicare toothbrush knew if you hadn’t changed the head. My surmise was it has an RFID reader built in and recognises the same old 4-byte code – until you change the head. When I changed the head I confirmed the old one had a RFID tag in. So I chopped the brush bit off and what remains is a workable test device – for “alien card” logic.
• Some hotel room cards also work.
• Some cards surprised me by not being RFID cards. Most notably the Oyster Card (used for getting round London).

Shrink To Fit

So there I am with my breadboard with a Pico W, 3 coloured LEDs, a resistor, and the RFID card reader hanging over the edge of it. This is clearly a fragile thing – and not at all portable.

The first thing to do was to replace the coloured LEDs with a RGB LED. This has 4 pins – Red, Green, Blue, Neutral. It’s much more compact than 3 LEDs. It’s easy to program.

The next thing I did was to find a plastic box to encase the circuitry in. This turned out to be a square makeup bud box. There are plenty of these I’ve harvested over the years. The plastic is quite soft so it was easy to cut a slot for the RFID reader’s wires and a small hole for the RGB LED. The RFID reader is stuck to the lid.

It won’t win any design awards but it gets the job done; It’s much more stable than the previous (breadboard-only) implementation. And here it is:

One small snag: Standard length (10cm) DuPont Wires are so long it was hard to shut the lid; It kept springing open. I looked for shorter (5cm) ones – in vain. So I decided to make my own. You can get a crimping tool and a set of wires and connector parts. I have to say this is fiddly in the extreme – especially with my old eyes. They say “practice makes perfect”. Well, it took a lot of practice. But finally the lid fits. I’ll probably have to solder the wires to the RGB LED. And then it might pass a shake test and I can consider it portable.

Conclusion

So this has been quite an adventure – through componentry and MicroPython programming and connector making. But I have something I use at least twice a day – “Start Day” and “End Day” being 2 cards that’ve ended up “In Production”. And 2 others kick off OmniFocus task creation and Drafts document creation.

Making Of

I realise USAns and probably others use the term “faucet” instead of “tap” – so the opening joke falls a bit apartment for them. Oops, I did it again. 😀

I started drafting this in Drafts on my iPhone – while running errands around London. And finished it on a flight to Istanbul.

Actually most of my posts are written in Drafts and then converted to HTML in Sublime Text, before being published via WordPress. This workflow works well for me, particularly as I can generate text (Markdown) anywhere in Drafts.

Signal is, of course, spotty on the underground- so link research was a bit fitful. A fortiori up in the air – where I’m not (yet) inclined to pay for WiFi.