[feat] Support Dymo Letratag 200b

[Bazoogle]

The Dymo Letratag 200b is a BLE label maker. The protocol is broken out well in this github repo: https://github.com/ysfchn/dymo-bluetooth

There is plenty of computer or web based implementations for communicating with this printer, but currently no open source app. It would be amazing if LaBLEr could add support for it so we could easily print without the Dymo app. I also recognize the protocol may be too different, and am not familiar enough with the subject to give valuable insight.

Regardless, thank you for the time and work in an open source effort.

[toolicious]

I was planning to restructure the printer side anyway, so that everything protocol specific is swappable and other printers can be added. This fits right in.

The protocol looks well documented, so I'll give it a shot. Problem is I can't test it myself, because I don't have the device. Any chance you'd be up for testing it? Realistically it'd take a few rounds back and forth.

[Bazoogle]

Any chance you'd be up for testing it? Realistically it'd take a few rounds back and forth.

I'd love to help! I am quite familiar with the trial and error required for something like this, so I have no problem going as many rounds as it takes. If you have logs exportable from the app setup, I'll use those, otherwise I can provide logcat logs whenever we run into an error. I'm not sure if the GATT exchange will be logged anywhere, but I have a feeling that would be very useful for me to upload if there are any issues with the BLE communication itself.

Since I know a lot of time could be spent waiting on responses, especially for small changes, I figure any method for reducing the back and fourth the better. Especially if I end up not having time to test for a day or two, I (or any other tester) could be quite the bottleneck. Essentially what I was thinking was in the test version of the app (or even better a toggle that could remain in the official app), where some variables could be edited from within the settings of the app without requiring rebuilding. Then I could adjust the values quickly and report the results without needing multiple compiled versions. While I recognize this would take more work to setup, I figure it could be beneficial for quicker testing with any future printer models as well. It's also entirely possible there are not enough variables that this would realistically apply to, making this suggestion moot.

We could also do parallel/multi-variant testing if needed, if there is an issue and we aren't exactly sure what needs to be changed. For example, rather than testing version A and waiting for a response, then testing version B and waiting for a response, you could send version A and B at the same time and I would report the results of both at the same time. And we could test n versions at the same time as needed so you don't have to keep waiting until I have time to run the next test.

Just let me know when you need assistance, I'm happy to help how I can.

[toolicious]

Thanks!

Build: https://github.com/toolicious/labler/releases/tag/v1.4.0-dev01

It's a dev build, so Settings has a Calibration section you won't see in a release. Basically your idea: the values I had to guess are editable there, so you can try them without waiting on me. The geometry test print also stamps its own settings onto the strip (160.0dpi 30x320 off1 rev), so a photo explains itself.

This has never run on real printer hardware, so start with the boring ones:

• Letratag… shows up under Settings, Find printer, without "Show all Bluetooth devices"
• it connects. If it complains about the Bluetooth packet size, post the message and your phone model and stop there, that one I can't work around
• a short text label prints
• print the geometry pattern (Settings, Diagnostics, Test print tools) and post a photo of the whole strip. Anything mirrored? Is the border two dots on all four sides? How tall is the printed strip in mm?
• measure between the two marks at the bottom, middle to middle, and type that into Settings, Calibration
• a ~100 mm label prints to the end, that one goes out in several chunks
• pull the cassette and print, and cancel a print at the device. Does the app say so either time?

If the pattern comes out wrong, everything to try is in that same Calibration section:

• mirrored top to bottom → turn off "Reverse the byte order of a column"
• border thinner on one edge → "Row offset inside the column" to 0
• prints fine but the app stays on Printing → turn off "Wait for the printer to report the result"

Logs: adb logcat --pid=$(adb shell pidof -s io.github.toolicious.labler.debug), ours are tagged LaBLEr.

The head is only 30 dots, about 5 mm, so text and 1D barcodes work but QR codes and photos probably don't. But please feel free to test this as well!

[Bazoogle]

This was my progress:

• Letratag… shows up under Settings, Find printer, without "Show all Bluetooth devices"
• it connects. If it complains about the Bluetooth packet size, post the message and your phone model and stop there, that one I can't work around

Unfortunately, the MTU size was incorrect:
Error: This phone negotiated too small a Bluetooth packet size for this printer (506 bytes needed)

I have a Motorola Edge 2021 running Lineage OS 21. I don't think my phone is the limiting device for the MTU size though. One of the things mentioned in the reference above was about the chunk size:

Each chunk must contain its index before chunk data itself followed by. The chunk data can be smaller than 500, but it can only contain maximum 500 bytes, inclusive.

While I know you said this cannot be worked around, I went ahead and got logs for both DYMO LetraTag Connect printing to the printer, and when LaBLEr attempted to connect. Here are what I believe to be the relevant portions for the MTU size:

DYMO LetraTag Connect successful print

[2026-09-02 18:33:25.082 Uid(value=10134):11571:11571 I/GH.WifiBluetoothRcvr]
Connection action: android.bluetooth.device.action.ACL_CONNECTED, device XX:XX:XX:XX:04:2E

[2026-09-02 18:33:25.083 Uid(value=10134):11571:11571 I/GH.WifiBluetoothRcvr]
Wireless projection is available on this phone.

[2026-09-02 18:33:25.090 Uid(value=10180):2585:2622 W/BluetoothEventManager]
AclStateChangedHandler: activeDevice is null

[2026-09-02 18:33:25.144 Uid(value=10140):21267:21346 D/BluetoothGattServer]
onConnectionUpdated() - Device=50:78:7D:AE:04:2E interval=21 latency=0 timeout=400 status=0

[2026-09-02 18:33:25.144 Uid(value=10462):10551:10570 D/BluetoothGatt]
onConnectionUpdated() - Device=50:78:7D:AE:04:2E interval=21 latency=0 timeout=400 status=0

[2026-09-02 18:33:25.437 Uid(value=10140):21267:21346 D/BluetoothGattServer]
onConnectionUpdated() - Device=50:78:7D:AE:04:2E interval=6 latency=0 timeout=500 status=0

[2026-09-02 18:33:25.438 Uid(value=10462):10551:10570 D/BluetoothGatt]
onConnectionUpdated() - Device=50:78:7D:AE:04:2E interval=6 latency=0 timeout=500 status=0

[2026-09-02 18:33:25.518 Uid(value=10140):21267:21346 D/BluetoothGattServer]
onPhyUpdate() - device=50:78:7D:AE:04:2E, txPHy=2, rxPHy=2

[2026-09-02 18:33:25.519 Uid(value=10462):10551:10570 D/BluetoothGatt]
onPhyUpdate() - status=0 address=50:78:7D:AE:04:2E txPhy=2 rxPhy=2

[2026-09-02 18:33:25.617 Uid(value=10462):10551:10570 D/BluetoothGatt]
onSearchComplete() = Device=50:78:7D:AE:04:2E Status=0

[2026-09-02 18:33:25.640 Uid(value=10462):10551:10551 D/BluetoothGatt]
configureMTU() - device: XX:XX:XX:XX:04:2E mtu: 247

[2026-09-02 18:33:25.661 Uid(value=1002):2883:3023 I/bluetooth]
gatt_process_mtu_rsp: Local pending MTU 247, Remote (xx:xx:xx:xx:04:2e) MTU 500

[2026-09-02 18:33:25.661 Uid(value=1002):2883:3023 I/bluetooth]
gatt_process_mtu_rsp: MTU Exchange resulted in: 500

[2026-09-02 18:33:25.663 Uid(value=10462):10551:10570 D/BluetoothGatt]
onConfigureMTU() - Device=50:78:7D:AE:04:2E mtu=500 status=0

[2026-09-02 18:33:25.679 Uid(value=10462):10551:10551 D/BluetoothGatt]
setCharacteristicNotification() - uuid: be3dd652-2b3d-42f1-99c1-f0f749dd0678 enable: true

[2026-09-02 18:33:25.717 Uid(value=10140):21267:21346 D/BluetoothGattServer]
onConnectionUpdated() - Device=50:78:7D:AE:04:2E interval=21 latency=0 timeout=400 status=0

[2026-09-02 18:33:25.728 Uid(value=10462):10551:10570 D/BluetoothGatt]
onConnectionUpdated() - Device=50:78:7D:AE:04:2E interval=21 latency=0 timeout=400 status=0

Failed LaBLEr Connection

[2026-09-02 18:38:27.750 Uid(value=10134):13360:13360 I/GH.WifiBluetoothRcvr]
Connection action: android.bluetooth.device.action.ACL_CONNECTED, device XX:XX:XX:XX:04:2E

[2026-09-02 18:38:27.756 Uid(value=10180):2585:2622 W/BluetoothEventManager]
AclStateChangedHandler: activeDevice is null

[2026-09-02 18:38:27.771 Uid(value=10134):13360:13360 I/GH.WifiBluetoothRcvr]
Wireless projection is available on this phone.

[2026-09-02 18:38:28.146 Uid(value=10140):21267:21347 D/BluetoothGattServer]
onConnectionUpdated() - Device=50:78:7D:AE:04:2E interval=21 latency=0 timeout=400 status=0

[2026-09-02 18:38:28.147 Uid(value=10455):5691:5706 D/BluetoothGatt]
onConnectionUpdated() - Device=50:78:7D:AE:04:2E interval=21 latency=0 timeout=400 status=0

[2026-09-02 18:38:28.463 Uid(value=10140):21267:21347 D/BluetoothGattServer]
onConnectionUpdated() - Device=50:78:7D:AE:04:2E interval=6 latency=0 timeout=500 status=0

[2026-09-02 18:38:28.464 Uid(value=10455):5691:5706 D/BluetoothGatt]
onConnectionUpdated() - Device=50:78:7D:AE:04:2E interval=6 latency=0 timeout=500 status=0

[2026-09-02 18:38:28.640 Uid(value=10455):5691:5706 D/BluetoothGatt]
onSearchComplete() = Device=50:78:7D:AE:04:2E Status=0

[2026-09-02 18:38:28.643 Uid(value=10455):5691:5691 D/BluetoothGatt]
configureMTU() - device: XX:XX:XX:XX:04:2E mtu: 517

[2026-09-02 18:38:28.664 Uid(value=1002):2883:3023 I/bluetooth]
gatt_process_mtu_rsp: Local pending MTU 517, Remote (xx:xx:xx:xx:04:2e) MTU 500

[2026-09-02 18:38:28.664 Uid(value=1002):2883:3023 I/bluetooth]
gatt_process_mtu_rsp: MTU Exchange resulted in: 500

[2026-09-02 18:38:28.666 Uid(value=10455):5691:5706 D/BluetoothGatt]
onConfigureMTU() - Device=50:78:7D:AE:04:2E mtu=500 status=0

[2026-09-02 18:38:28.669 Uid(value=10455):5691:5691 D/BluetoothGatt]
cancelOpen() - device: XX:XX:XX:XX:04:2E

[2026-09-02 18:38:28.673 Uid(value=1002):2883:3023 I/bluetooth]
gatt_update_app_hold_link_status: removed gatt_if=7

[2026-09-02 18:38:28.673 Uid(value=1002):2883:3023 I/bluetooth]
disconnect: Device: xx:xx:xx:xx:04:2e, cid: 0xffff

[2026-09-02 18:38:28.673 Uid(value=10455):5691:5691 D/BluetoothGatt]
close()

[2026-09-02 18:38:28.673 Uid(value=1002):2883:3023 W/bluetooth]
disconnect: no eatt device found

[2026-09-02 18:38:28.673 Uid(value=1002):2883:3023 I/bluetooth]
gatt_update_app_use_link_flag: GATT fixed channel is no longer useful, start link idle timer for 1 seconds

[2026-09-02 18:38:28.673 Uid(value=10455):5691:5691 D/BluetoothGatt]
unregisterApp() - mClientIf=7

[2026-09-02 18:38:28.675 Uid(value=10455):5691:5706 D/BluetoothGatt]
onClientConnectionState() - status=0 clientIf=7 device=50:78:7D:AE:04:2E

[2026-09-02 18:38:28.676 Uid(value=1002):2883:3023 W/bluetooth]
gatt_update_app_hold_link_status: attempt to remove non-existing gatt_if=7

[2026-09-02 18:38:28.676 Uid(value=1002):2883:3023 I/bluetooth]
gatt_update_app_use_link_flag: App status is not updated for gatt_if=7

[2026-09-02 18:38:28.682 Uid(value=10455):5691:5712 I/LaBLEr]
reconnect skipped: no saved printer

Idk if this is useful, but the DYMO LetraTag Connect app works a bit different from LaBLEr. You fully design the label and click print, and you never even select a printer. It just sends it to the printer as long as it finds it. The app does require location permissions, though it's not entirely clear to me why that is.

I have attached more full logs of each scenario in case it is helpful. I did include wider bluetooth logs as well.

LT Connect Print.txt
LaBLEr Attempted Connect.txt

[toolicious]

Thanks, fixed. I had read the 500 bytes as a required chunk size, so the app asked for an MTU your phone was never going to give it (it's a maximum, not a minimum). Now it cuts the chunks to whatever the connection actually offers. Your 497 usable bytes come out as chunks of 494.

The logs were worth the effort by the way. Seeing the vendor app ask for 247 and get 500 back made it obvious that the negotiated size has nothing to do with the requested one.

I now also copied the bit where the vendor app skips chunk index 27. Nobody seems to know why it does that, the reference implementation has a TODO sitting next to it, but with smaller chunks a job actually gets that far now.

New build: https://github.com/toolicious/labler/releases/tag/v1.4.0-dev02

Same debug build as before, so the four values under Settings and the logging are still in. Same list as last time, starting again at the connect.

[Bazoogle]

Great news! It prints!

The calibration was a little confusing. I measured a distance of just over 15mm, nowhere near the 30mm. When setting it to what I measured, the dots didn't move but the print did get longer.

It never communicates the print status, whether success, fail, or canceled. It always stays "Printing..." in the top right from the test page, and when in the regular label page it doesn't give an indicator (it still just says "Print"). In both cases, the back button would not work while it was printing and would effectively freeze the app. I had to fully close the app to be able to do anything.

The details:

• Letratag… shows up under Settings, Find printer, without "Show all Bluetooth devices"
• it connects.
• a short text label prints
• print the geometry pattern (Settings, Diagnostics, Test print tools) and post a photo of the whole strip.
  • Anything mirrored? No
  • Is the border two dots on all four sides? I'm not sure what you mean
  • How tall is the printed strip in mm? About 4.75mm
• measure between the two marks at the bottom, middle to middle, and type that into Settings, Calibration
  • Assuming I measured the correct lines, I measured it to be just about 15mm
• a ~100 mm label prints to the end, that one goes out in several chunks
  • After calibration, I got to about 90mm. From the logs, it seems multiple of the prints had several chunks that worked.
• pull the cassette and print, and cancel a print at the device. Does the app say so either time?
  • No response from app regarding status of print, success, fail, or canceled

The below images shows the two test patterns, the third one is a print using the "Text Sample" under the test prints, and the last one is printed using the settings shown in the screenshot.

Prints

Hello World print settings

Measuring Test Print Pattern

Here are logs I captured, though I don't think there's much useful information since there aren't as many specific things to address:
LaBLEr Initial Pairing.txt
LaBLEr Successful Test Print.txt
LaBLEr Canceled Test Print.txt
LaBLEr Printed with no Casette.txt

Side note: Under "Calibrate printed length" it says "Measured in mm" for a second it was confusing because I though "in" was the abbreviation for inches. I believe this is not staying in the production version, so this wouldn't matter anyway.

[toolicious]

Thanks! What I got out of it:

• The tape advances at twice the resolution of the head, 160 dpi across and around 320 along. Everything was coming out half the length and half the width, which is why the text in your photos sits narrower than it was drawn.
• A label is now laid out on square dots and stretched onto the printer's columns when it prints, so the proportions come out right.
• The app waited a flat 60 seconds for the printer to report back and kept the print sheet shut for all of it. It now waits as long as the label takes, about 11 seconds for the test pattern, and the sheet closes while the job runs.
• Every notification the printer sends goes into the log now. If it does report something and I was misreading it, the next log will say so.
• The built-in text sample was sized for a head three times as tall, hence the cut-off bottoms.
• The calibration field no longer says "in mm" to avoid confusion.
• The 4.75 mm you measured is all the hardware gives: 30 dots at 160 dpi cover 4.76 mm of the 12 mm tape, so the empty space above and below it is not something the app can fill. Does the Dymo app leave the same margins? If it prints any taller, I am dropping a row somewhere.

Before you print anything, hit Reset next to the calibration value in Settings. Your 318.8 would otherwise sit on top of the new default and the measurement would say nothing about it.

After that the two marks on the test pattern are about 30 mm apart instead of 15, so measuring them again is twice as precise as last time and costs no extra tape.

New build: https://github.com/toolicious/labler/releases/tag/v1.4.0-dev03

[Bazoogle]

As far as hardware goes, this version seems to work without any issues!

• The test pattern print was correct, at exactly 30mm
• The proportions came out correctly
• The height is the same on both LaBLEr and the Dymo app
• Cancelling was recognized correctly
• It seems to correctly say it printed in the app after printing finished

It does not recognize when the printer has no cassette, but I do not think the printer is reporting that at all. It seems to me that the printer is trying to print even when the lid is open/there is no cassette, the only difference is the thermal head and roller are not pressed against the label tape to actually print. So the motor runs and the thermal head heats up as if it were printing but nothing is printed. Ultimately there is no way to detect this, they probably did it this way because it's cheaper (I got this one for $20 USD). I think it makes the most sense to just assume it was a success, even if it technically could have failed to print.

The built-in text sample is now extremely small, lol.

I have added on additional labels from the test prints, starting after the previous cut off Hello World print it goes:

1. A previous test print where I printed inserted it back into the printer and over it from the DYMO app the letters "HAPQ" (Just random letters with distinct shapes) as large as I could make it. The Dymo app takes up the same printing space as the prints from LaBLEr
2. A test print from the most recent debug version, with markers at 30mm difference
3. Sample text printed again, this time it was very small
4. A "Hello, World!" test print again, with the settings shown in the second screenshot below.

Print Results

Settings for custom test print

LaBLEr Successful Print 2.txt
LaBLEr Canceled Print 2.txt
LaBLEr No Cassette 2.txt

As far as I can tell, everything is fully working on the hardware. There's a couple changes that would help in the editor, since it is such a small printing space on this printer. To keep it brief, the easiest one is that it'd be nice if the editor showed the full height of the label tape (12mm) but cut off any text outside the printable area, to represent what it will actually look like when printed. I want to utilize the full space of the printing area, but it can be difficult trying to move it all the way to the edge of the preview window when creating a label. I have some other ideas, but I can put those in different feature requests to keep the requests organized.

Was there anything else you wanted me to test and upload from the printer?