Feature #4030


design breakout board for GTM900-B

Added by laforge over 4 years ago. Updated 4 days ago.

In Progress
Target version:
Start date:
Due date:
% Done:


Spec Reference:


Let's build a small 2-layer PCB design as a break-out board for the calypso/iota/rita based GTM900-B module.

It should have the following key features:

  • on-board power supply for (5V?) input
    • over-voltage + polarity protection
  • 2.5mm jack for the UART (+ TVS array)
  • expose all pins of the module on 2.54mm header
  • LED for power and modem (is there one?)
  • power button and jumper in parallel (auto-start)
  • reset button
  • SIM card slot (2FF) with TVS array

One option would also be to directly put a CP2102 or even CP2105 on the board to attach to one (or both) UARTs. This way we'd also have the option to control reset and/or power via GPIOS or serial status lines, like tsaitgaist used to do..


GTM900.pdf View GTM900.pdf 1000 KB laforge, 05/28/2019 10:10 PM
GTM900_product_overview.pdf View GTM900_product_overview.pdf 994 KB Product overview (Chinese), more detailed and more schematics than in English version steve-m, 09/02/2019 09:34 PM
gtm900-audio-io-symm.png View gtm900-audio-io-symm.png 7.28 KB gtm900-audio-io-symm mschramm, 05/04/2020 06:37 PM
gtm900-audio-io-asymm.png View gtm900-audio-io-asymm.png 7.59 KB gtm900-audio-io-asymm mschramm, 05/04/2020 06:37 PM
lenovo-combo-audio-jack.jpg View lenovo-combo-audio-jack.jpg 26.2 KB lenovo-combo-audio-jack mschramm, 05/04/2020 06:37 PM
PWON_chinese-ds.png View PWON_chinese-ds.png 14.6 KB PWON_chinese-ds mschramm, 05/04/2020 06:40 PM
PWON_english-ds.png View PWON_english-ds.png 15 KB PWON_english-ds mschramm, 05/04/2020 06:40 PM
gtm900-bo_modem-side.jpg View gtm900-bo_modem-side.jpg 98 KB mschramm, 06/04/2020 03:27 PM
gtm900-bo_smt-side.jpg View gtm900-bo_smt-side.jpg 142 KB mschramm, 06/04/2020 03:27 PM
gtm900-bo_smt-side_proto-placed.jpg View gtm900-bo_smt-side_proto-placed.jpg 158 KB mschramm, 06/10/2020 08:20 PM
GTM900-breakout-schematic.pdf View GTM900-breakout-schematic.pdf 49.2 KB GTM900-breakout-schematic mschramm, 06/10/2020 08:45 PM
GTM900-breakout-schema_v2.pdf View GTM900-breakout-schema_v2.pdf 52.3 KB mschramm, 02/21/2022 07:25 PM
gtm900-bo_v2-headsetparade.jpg View gtm900-bo_v2-headsetparade.jpg 158 KB mschramm, 11/20/2023 11:23 PM
gtm900-bo_v3-freshPCBs.jpg View gtm900-bo_v3-freshPCBs.jpg 204 KB mschramm, 11/20/2023 11:23 PM
gtm900-bo_v3-freshPCBs-populated.jpg View gtm900-bo_v3-freshPCBs-populated.jpg 202 KB mschramm, 11/22/2023 09:55 PM


  • UART A
  • UART B
  • Audio on 3.5mm jack[s]
  • power supply
  • mechanical mounting of GTM module
  • power button control via modem handshake (optional via jumper)
  • mounting holes of breakout board

Related issues

Related to OsmocomBB - Feature #4575: Build + Test CP2102 GTM900 breakout board prototypeClosedroh06/02/2020

Related to OsmocomBB - Bug #4610: OBB port on GTM900-B risks causing hw damage with fighting driver outputs on Calypso GPIO3/DTR lineResolvedlaforge06/10/2020


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