I'm not getting it to work!

First thing to try is the power up test. You do not need an arduino for this

Make sure the paper is in the bay correctly, it should feed under and up so that the paper comes through the slot without bending

Hold down the button on the top, then plug in the printer to power. It should print out a test page

The green LED will not be on solid, it will blink once in a while, that's normal.

I'm trying the self test and it's still not working.

Make sure you have a good power supply that can deliver the required current. If you are trying to operate at 5V, your power supply must be able to maintain a constant 5V even when the current demand spikes during printing. If your printer is making an attempt to print, but then struggling, then it is likely your power supply is dipping below 5V.

If possible, try a higher voltage power source. At 9V you should be able to get away with 1A.

I'm having difficulty getting a printout

Make sure the paper is in the bay correctly, it should feed under and up so that the paper comes through the slot without bending

Make sure the paper roll is not 'stuck' feeling in the bay, it should rotate easily!

My Arduino sketch used to work, but doesn't compile now!

Some changes have been made to support a broader range of Arduino-like boards. Older code will require updating. Fortunately it's just a few lines around the global declarations and the setup() function.

Old syntax:

Adafruit_Thermal printer(RX_PIN, TX_PIN);

New syntax: declare a SoftwareSerial object and pass its address to the Adafruit_Thermal constructor, like so:

SoftwareSerial mySerial(RX_PIN, TX_PIN); 

Adafruit_Thermal printer(&mySerial);

Then, in the setup() function:



My sketch compiles, but the output is different than before.

The printer's features and behavior have changed over various firmware releases.

First, check the PRINTER_FIRMWARE value in Adafruit_Thermal.h, make sure it matches the value at the bottom of the printer test page (hold down the paper feed button when connecting power to print out a test page).

Some features just behave a little differently among releases…barcodes, line feeds, etc.…if you were previously using an older library or an older printer, you may need to tweak the code to produce the desired formatting with a current setup.

The USB printer is not showing up as expected.

The printer might be in a different mode. To check and change the current USB mode, do the following:

  • Similar to self test - hold in the FEED button while applying BUT KEEP HOLDING IT (see below).
  • You should get an extra bit of output that will tell you the Current USB mode. It should say COM.
  • If it doesn't say COM, then change the USB mode by holding the FEED button again for 2 seconds.
  • It should print the new USB mode and then exit.
  • Done.
This guide was first published on Sep 02, 2012. It was last updated on Sep 02, 2012. This page (Troubleshooting!) was last updated on Apr 23, 2019.