Over the last few weeks, I’ve been playing with a few small thermal printers. Meant as POS or information booth printers, they make a diverting project for the lo-fi printing enthusiast. While they all have common features — 58 mm/2¼” paper width, 8 pixel/mm resolution, 48 mm print width, serial connection — they all have their quirks. You may have seen these sold as the Adafruit Mini Thermal Receipt Printer or Sparkfun’s Thermal Printer, but there are many others. I’m going to write more on interfacing these directly to Raspberry Pi, Arduino, and (if I can navigate the documentation) a CUPs driver.
For now, I’m just leaving you a list of things I’ve found helpful for the DP-EH600 and 701 printers. Note that the similar-looking BTHT-v6 printer uses a completely different command set.
- Replacement paper is sold as 2¼” × 30′. Staples have a box of 30 rolls for under $25 (item 279096, not on their website). Longer rolls don’t fit.
- You’ll need a USB→TTL Serial adaptor, preferably one with DTR control. I use one from JY-MCU. In a pinch, you can use a simpler Debug / Console Cable for Raspberry Pi, but you risk serial overruns and dodgy results. Remember that RX on the adaptor goes to TX on the printer, and vice versa.
- A good solid power supply is needed; these printers draw ~8 W when printing. Some printers only support 5 V (for which a 3 amp adaptor would be ideal), others 5-9 V. The higher voltage makes text printing faster. You can’t drive these directly from your Raspberry Pi/Arduino power supply.
- Linux serial ports are set to some defaults which may have been historically useful, but now corrupt 8-bit data. A trick I picked up here is to first issue the command
stty -F /dev/ttyUSB1 0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0
which clears all settings, then set the device up as you need it:
stty -F /dev/ttyUSB1 speed 9600 raw cs8
(Most of these printers default to 9600 baud. Your device may be called something different to ttyUSB1.)
- I’ve written a couple of Python driver stubs which take an image and produce the relevant binary output:
- scruss / esc-pos-image.py – prints an image as a single command. May not work on the SparkFun printer. Does not work on the BTHT-v6.
- scruss / esc-pos-image-star.py – prints the image in 24 pixel deep bands. Can sometimes cause visible gaps in the printout, but will work on almost all printers, except the BTHT-v6.
- These Python libraries also work, as long as you address the printer properly (right device, right speed):
- Reed Zhao (of Tangram Software) lent me a couple of different printers for testing after I bought a different one from him. He’s put a lot of work into sourcing these printers direct from the manufacturers. Thanks, Reed!
- Image credits for print samples: