21 November 2018

Sending fragments of data to a microcontroller

Alright. I have (autogenerated) a new problem to solve: I want to be able to send few bytes of information to a microcontroller installed into a box without using a physical input device (a.k.a. "button"). This operation has to happen more than rarely, so I would like to avoid throwing in some hardware that potentially will never be used or would lock me in to an external technology. At one-off production run it is purely a stylistic affair, not a cost-cutting measure.

Specifically, the device is a digital clock and I want to be able to set the time without extra drilling the box and installing a button. So "wirelessly". There are two holes, one for DC input socket and one for the Nixie tube protruding out of the cover. The display acts as a feedback to the user, of course.

My night-long brainstorming came up with these options:
  • Plain old button(s) requires an extra hole.
  • WiFi or Bluetooth are too power hungry, too costly, too technically advanced because they require a software counterpart.
  • A reed switch, but the box is quite thick and it requires a powerful magnet that might not be available when needed.
  • An IR receiver under the Nixie and a TV remote as remote controller that might not be available when needed.
  • A microphone to receive AFSK or similar, but requires a software counterpart.
  • An open capacitor to take advantage of hand proximity effect.
  • A LDR under the Nixie tube and operator's hand to command through shade/light.
  • A tilt sensor, not the cheapest way.

The following table summarises my options:

Type Hole? Extra tech?
Button Y N
WiFi / BT N Y
Reed switch N Y
IR receiver N Y
Microphone N Y
Open capacitor N N
Tilt sensor N N

I like the last two the most. Both LDR and tilt sensor are hand-operated and allow for an easy repurpose too: at powerup they serve as input devices to set the time, during operation they can provide information to control brightness.

I need to verify whether the LDR under the Nixie receives enough light to understand "light vs shade" situations. Otherwise I will order a tilt sensor.

Readers, please leave a comment if you have further interfacing ideas!

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