Feature #4030

design breakout board for GTM900-B

Added by laforge 7 months ago. Updated 3 months ago.

In Progress
Target version:
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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


#1 Updated by laforge 7 months ago

The shortest 40pos 0.5mm pitch FPC available from Digikey seems to be at 29.97mm.

#2 Updated by mschramm 6 months ago

GTM900 exposes no LED at all, so the breakout only will get a power-on LED.

Should the modem reside on the break-out PCB like on the mPCIe adapter, e.g. with hex spacer, or will this board be much smaller for only carrying the additional functionality and not the modem itself?

#4 Updated by laforge 6 months ago

  • Priority changed from Normal to Low

the modem should be mounted with spacers on the board. I typically want to have a mechanically stable configuration, without any pigtails or other fragile constructs hanging off it. That's why we have the SMA sockets on the mpcie breakout board, and why I believe we should have a similar construct here.

#5 Updated by mschramm 6 months ago

mschramm wrote:

GTM900 exposes no LED at all,

this might be not true, there are two pins with funny names and ambiguous descriptions, so likely one of them (or both?) might drive a LED (plus aditional driver):

Pin 13 is VDD (output), and its function "signal indication of normally started GTM900". The other is pin 32, LPG (output), "mainly controls the status of the indicator".

#6 Updated by mschramm 3 months ago

  • Status changed from New to In Progress

#7 Updated by steve-m 3 months ago

mschramm wrote:
Pin 13 is VDD (output), and its function "signal indication of normally started GTM900". The other is pin 32, LPG (output), "mainly controls the status of the indicator".

LPG is "LED pulse generation", basically dedicated timer circuitry to let an LED blink. Currently it is configured to have the LED always on, which works on the GTM900 on the existing breakout-board from China.

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