Party printer project

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It's a box that prints things.

This was made as a selfie thing at a party - at the height appropriate for an erotic party, in fact - with the idea that it was just high quality enough to be recognizable but not very identifying.


And also cheap to run - thermal rolls cost very little, and require no ink.


The printer is a thermal printer, the kind that prints receipts at a checkout. This means you don't need to worry about ink, and the paper isn't very expensive - or particularly wasteful, being small.

It turns out most POS printers (there's not a lot of difference) do around 200dpi at least (more is rarely useful), so can print a decent image if you tell it to do more than letters, and massage the image beforehand.


In the box

  • a power strip
makes image processing easier than on a uC
  • an access point (and power supply)
Using an old AP makes it easy for this to not depend on the environment's WiFi, and a hidden network is a nice little detail.


Currently a HS802UL (USB and network), I previously broke a Star TSP600 (serial)
one with a cutter is nice, though tear-off also has its charm
I would recommend trying to find one with network interface, because serial interface is rather slower, and potentially finicky (particularly if you don't have proper flow control, networking comes down to 'open TCP connection and send data')
  • some creatively positioned plastic and wood for separation and positioning of all the parts


With a little image massaging (contrast enhancement and in particular dithering), the quality is better than you'ld probably expect from a 58mm (2.3") receipt. It'll look a little worse if you use a webcam in lower lighting as we did
It makes random-wordy decoration


Alongside:

  • A WiFi-capable IP camera
Here a DCS-930L, but any should do, as long as it exposes an URL to fetch the current image from without too much trouble

The code

Capturing from the IP camera is continuous, and we detect a sudden increase in brightness, collect a number of candidates, and choose the best.

It's done this way because it means we can trigger with a button that lights a lamp, avoiding any wiring on both sides, and means we can place the box elsewhere, in a safer place.


Various POS printers speak their own proprietary and more capable protocol, but most should be able to speak ESC/POS, a relatively basic protocol, which means fairly simple code should work for most POS printers.


Say, that decoration is mostly just sending strings, alternated with cut commands.


The conversion to an image is slightly more involved, because aside from the image massaging, there's also conversion into a 1-bir image, and packing it into bits one a row at a time.