Tutorial: Thermal Printer, Part 1: Hardware Setup with FRDM Board

One of my embedded projects is to measure the running time in a sports event (see “Sports Timing System in a Lunch Box“). The recorded time is stored in an EEPROM plus sent over USB or wireless connection to the host. It would be great if I could print out the time and ranking directly, so if there is no PC, the system can be small and tiny. So here is my next project and tutorial: Printing with the Freedom board!

Hello World on the Printer with FRDM-KL25Z

Hello World on the Printer with FRDM-KL25Z

The ability to print is a great addition to any other project: I can send messages to be printed out on a remote board, using it as a receipt printer, logging test results and many more things: having printing capabilities is such a great addition to any project, and it does not take much! I have spent this Sunday morning only 4 hours from unpacking, connecting the hardware, programming the first software with CodeWarrior+Processor Expert until I had a “Hello World from the FRDM-KL25Z!” showing up on the printer! And that 4 hours included writing this tutorial :-). So expect it would take you less than one hour with the help of this tutorial.

First Hello World Message on Printer

First Hello World Message on Printer

Adafruit Mini Thermal Receipt Printer

I ordered a small thermal printer from Adafruit (http://learn.adafruit.com/mini-thermal-receipt-printer) which costs $50. I added three thermal paper rolls (http://www.adafruit.com/products/599) to my order to have enough paper to start with :-):

Adafruit Mini Thermal Printer

Adafruit Mini Thermal Printer unpacked

The main features of the printer (from the data sheet):

  • Thermal paper printer, 2.25″/57mm wide (effective printing width 48 mm)
  • Built-in fonts: small, medium, large text
  • Bold, underline and inverted text with left/right/center positioning
  • Different bar codes
  • Printing monochrome bitmaps and images
  • Size: 111x65x57 mm
  • 5-9V DC, 1.5 A
  • TTL Serial (RS-232, 5V) protocol

Useful links:

With the printer came a test print which has the baud listed. There are printers with 9600 baud and others with 19200, mine came with 19200. More about this later.

Printer Test Print with Baudrate

Printer Test Print with Baudrate

Mounting and Connectors

The two brackets are for mounting the printer behind a panel. In order not to lose the parts, I mounted them right away:

Adding Printer Mounting Brackets

Adding Printer Mounting Brackets

The cables get connected to the backside of the printer:

Printer Backside Connectors

Printer Backside Connectors

Power Supply

The printer requires a 5-9V power supply. Thermal printing needs a lot of power, so a 1.5 amps power supply is needed! There are many ways how you could give power to the printer. I usually have always a bunch of power supplies, but the challenges is that the plugs never match my needs. So usually I end up cutting the wires and making it fitting my needs. For this project I use a 5V 2A power supply I have left over from a damaged Cisco router:

5V 2A Power Supply

5V 2A Power Supply

I cut the 5V wires:

Power Supply 5V Wires cut

Power Supply 5V Wires cut

Same for the printer supply wires:

❗ Cut the wires on the 2-pin connector (NOT on the 3-pin side)!

Cutting Printer Supply Wires

Cutting Printer Supply Wires

Then remove the isolation:

Removed Isolation

Removed Isolation

I’m using heat shrink tubes for isolation, but you can use electrical isolation tape too (not so nice as heat shrink tubes). I cut pieces of different diameter and size:

Shrink Tubes

Shrink Tubes

Put them on the wire before soldering:

Shrink Tubes on Wires

Shrink Tubes on Wires

Wrap the wires together:

❗ carefully check the wire polarity (what is plus, and what is ground)! In doubt, use a voltage meter to verify it!

Wires Wrapped together

Wires Wrapped together

Solder the wires:

Solder the Wires

Solder the Wires

Then use a hot air gun to shrink it:

Shrinking with Hot Air Gun

Shrinking with Hot Air Gun

The result is a nice connection:

Shrinked Power Cable

Shrinked Power Cable

Inserting Paper

When powered, the green LED flashes. There is a ‘Paper Feed’ button plus a lever to open the printer.

Printer button, led and lever

Printer button, LED and lever

A roll presses the paper on the printer head:

Paper Press Roll

Paper Press Roll

The printer head is near the ‘cut off’ area:

Printer Head

Printer Head

The paper is placed inside the printer. Make sure the paper is clean and has no stickers/etc on it:

Paper inside the printer

Paper inside the printer

Then close the cover:

Printer Cover Closed

Printer Cover Closed

 Making a Test Print

Powering the printer with the ‘paper feed’ button pressed will print a test report:

Test Print with Baudrate

Test Print with Baudrate

Now I’m sure my printer is working 🙂

Printer Connection to the FRDM Board

There is problem: the printer uses 5V (TTL) logic levels, while my FRDM board has 3.3V levels. The printer accepts 3.3V input values (on the printer RX line), but it would be a bad idea to connect the printer output 5V TX signal to a microcontroller having 3.3V levels without a level shifter.

Printer Tx and Rx

Printer Tx and Rx

As I’m only sending data to the printer, I’m *not* going to connect the printer 5V Tx line to my board. I’m only connecting the GND and the microcontroller Tx with the Printer Rx. For this I’m using connector cables:

Printer to Microcontroler Connection

Printer to Microcontroler Connection

Ground is connected to the board GND pin. I’m free to use any available UART Tx pin, and I have used UART0 Tx (Port A, pin 2) PTA2:

FRDM-KL25Z Connections

FRDM-KL25Z Connections

Summary

In few hours, I have now the ability to print at least some text, using the FRDM-KL25Z and the Adafruit thermal receipt printer. Much faster than I have expected, which is a great thing. Time for having lunch. A next post will be about how to use the software.

But if you cannot wait: the project is already on GitHub: https://github.com/ErichStyger/mcuoneclipse/tree/master/Examples/FRDM-KL25Z/FRDM-KL25Z_Printer

Happy Printing 🙂

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14 thoughts on “Tutorial: Thermal Printer, Part 1: Hardware Setup with FRDM Board

  1. I have seen on the web and there are many tutorials with Arduino, you could see a little tutorial with PIC or have a library for PIC, before buying I would be sure that it works with the PIC ?

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    • I’m not using PIC with this printer, so I cannot comment much. But as long as the PIC is able to write to a UART, and has the correct logic levels, then I don’t see a reason why it would not work with a PIC.

      Like

  2. Hi ,
    It seems good work in a short span of time. Actually I’m working on the same project. But we here have a custom board . I just wanted to know how you are saving the data to print. . I’m storing hex values which I got converted from a bit map image using the software lcd assistant mentioned in the same website of adafruit. …

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    • Yes, Adafruit has a conversion utility (I have not used it much), but in general you can use any utility which transforms the bitmap into hex values.
      I plan to write a follow-up tutorial about different fonts and using graphics.

      Like

  3. Hi, I tried to send a hex command to another board just like your method, but it failed. i wander if it’s the cw problem because when i import the helloworld project without any change it will run correctly, but if i change the consoleio band to 19200 from 115200, then click “generate code”, then run it on kl25z, it will run uncorrectly, the getchar() will read infinitely FF. Can you give me some tips?

    Like

    • Can you verify the 115200 baud with an oszilloscope to make sure you get that speed? Other than that, I would try and verify if things work with lower speed to isolatethe problem.

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      • it seems that it’s because i use the 5v usb out pin in j9 to supply the power for another board, when i charge the board with another battery, it works. but the band change problem still confuses me a lot.

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        • That 5V USB out pin can only drive a limited number of mA (you need to check the data sheet). That is typically enough to power some small loads (less than 100 mA I think), but for sure not more. So this is probably your problem.

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  4. Hi Erich,
    Great article..!! It made my day… 🙂
    I was wondering if you could give the link to software tutorial too.. I’m unable to print anything, The Tx signals from my mk10 mc are being transmitted to printer(checked using multi-meter) but nothing is being printed. Kindly help me out… 🙂

    Micro controller in use: MK10DN64VLH5
    Thermal Printer: EPM207 – HRS

    Thanks in advance.
    Looking Forward for your response.

    Regards,
    Sagar

    Like

    • Hi Sagar,
      checking the signal with a multimeter is not enough: check them with a oszilloscope or logic analyzer if they match the baud for your printer.
      I hope this helps,
      Erich

      Like

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