From mychaela.falconia at gmail.com Mon Jan 20 04:35:42 2020 From: mychaela.falconia at gmail.com (Mychaela Falconia) Date: Sun, 19 Jan 2020 20:35:42 -0800 Subject: Breakout adapter board for GTM900 modem modules Message-ID: Hello FC community, While we don't have much in the way of new development activity, the principal goals of FreeCalypso are still here and will never go away; one of these goals is to make our published-source modem solution available to anyone who desires it. In other words, if someone desires a standard GSM/GPRS modem that can run our FreeCalypso modem firmware, I consider it my duty to provide as many options as possible for such users. At the present time there are 3 hardware options that can run our FC firmware: (1) our own FCDEV3B, (2) Huawei GTM900-B discovered last year by Comrade Songbosi and (3) a recently discovered modem module that has been codenamed Tango. When it comes to our own FCDEV3B, I currently have about 10 boards which I would be happy to give away free of cost to worthy recipients, but so far no one has claimed even one of them. I have to say that I don't really understand why no one has taken some of these boards off my hands yet: perhaps it is the stipulation that they may not be used for the antisocial purpose of running OBB software, or perhaps people just aren't comfortable with asking to receive on a no-cost subsidy basis something that actually costs about $500 at break-even. Given this situation of no one taking up my offer of subsidized FCDEV3B boards, and considering other possibilities where someone may desire a published-source modem module that is physically smaller and suitable in terms of form factor for integration as a component into larger systems, I have been exploring ways to make other options more accessible as well, particularly the GTM900 option, and so I have produced this little board: ftp://ftp.freecalypso.org/pub/GSM/FreeCalypso/mmtb1.tar.gz A bare GTM900 module is not particularly usable by itself: one needs to break out the 40-pin FPC/FFC interface and connect power and at least one of the UARTs at the very minimum, whereas a more complete setup would involve connecting both UARTs, a SIM socket, PWON and RESET pushbuttons, earpiece and microphone. Songbosi did provide a "dumb" breakout adapter that turns the 40-pin FPC/FFC interface into a 40-pin 2.54 mm header, but it was very inconvenient, not really conducive to using the GTM900 in an FCDEV3B-like manner, so I sought out to produce a better (more specialized) breakout adapter board for these GTM900 modules, and the result is the MMTB1 linked above. The linked tarball contains schematic, PCB and gerber files, and I have physically produced one of these boards to prove the design as good. This GTM900-B modem module is certainly nowhere near as nice as our own FCDEV3B or Tango: FCDEV3B is triband, Tango is fully quadband, but GTM900-B supports only 900 & 1800 MHz bands, no "American" bands at all. There also exists another variant called GTM900-P which supposedly supports 850 & 1900 MHz bands (while NOT supporting the two "EU" bands), but I am not currently able to test that hypothesis because I have reached the limit of how much money I can dump into this passion, and I am no longer willing to buy a GTM900-P for testing with my own money. Therefore, if someone would like to see this GTM900-P potential option properly tested and supported, they would need to buy a GTM900-P module at their expense and send it to my address in California - then I will test it in my MMTB1+CMU200 setup and add the necessary support as appropriate. The other commonly encountered variant is GTM900-C, but it is known to NOT work: it has the LoCosto chipset inside instead of Calypso, so it is a no-go unless you wish to start your own FreeLocosto project and spend a few years bringing it up to a state comparable to where FreeCalypso is today. But despite its limitations, this GTM900-B module seems to be the cheapest and most accessible option at the present time: FCDEV3B is a development board not meant for integration as a component into larger systems, Tango is not currently a viable option because I am not able to disclose its real name until and unless someone pays for my SRS (for anyone considering that option, this Tango module is the absolute best Calypso modem ever, and the available stock is many thousands of pieces), thus we are left with just GTM900 for now. If I am not mistaken, Comrade Songbosi still has the GTM900-B version available in large qty for just $15 apiece. If someone is designing some larger system such a ZeroPhone-style smartphone, desires to use a GSM modem module that runs or can run firmware with fully published source code and chooses the GTM900 as that modem module, they would need to design their system to interface directly and natively to GTM900's 40-pin FPC/FFC connector. But if someone needs to test this GTM900 modem by itself first, just to see it working before committing to a design, they would ideally need a breakout adapter board like my MMTB1 to exercise the GTM900 by itself on a lab bench. Therefore, it would be really nice if these MMTB1 breakout adapter boards could be made easily and inexpensively available to individual hobbyist tinkerers. Now that I have published the design files, anyone can produce these simple MMTB1 boards (the design of this MMTB1 is in the public domain, unlike FCDEV3B). If I am to produce them here in California, I would need a minimum order of 20 pcs, and the price will be $50 apiece. The dominant cost component is assembly labor: the PCB is about $4 apiece, the components are about $16 total per board, but assembly is $25 apiece in the qty of 20 pcs. Doing smaller quantities would be absolutely uneconomical: to assemble just one board I was charged $250, so at that price you would be better off going for FCDEV3B - speaking of which, a batch of 20 FCDEV3B boards (once again the minimum production batch size) would cost $300 apiece if done as a single batch. If someone wishes to order a batch of 20 FCDEV3B boards at $300 apiece as a commercial order, I would be willing to waive the strict prohibition against using those boards for the purpose of running OBB software if the purchaser would be willing to sign a legal liability waiver. The purchaser would need to (officially, with a paper trail) understand and agree that OBB software running on Calypso hardware (be it Motorola or FreeCalypso) has been demonstrated and proven to put out radio transmissions that are in violation of GSM specifications and very capable of causing interference and disruption to GSM and other cellular networks, and therefore anyone who runs OBB on an FCDEV3B in open air (no Faraday cage, no cabled setup w/o antennas) would be not only causing interference and disruption to cellular networks, but doing so knowingly and willingly, which implies a significantly higher level of criminal culpability. Back to MMTB1, because it is just a passive breakout adapter and does not contain any actual GSM radio functionality (all of the latter is in the Huawei-made GTM900 piece), MMTB1 can be produced and sold without caring how it will be used and with what software - if someone wishes to turn their GTM900-B modem into a rogue transmitter by way of OBB software, it would be 100% their culpability - there is no conceivable way how a maker or distributor of a GTM900 breakout adapter board could be held liable. It would be nice if someone like Harald/Sysmocom could make these MMTB1 breakout adapter boards available in a webshop (perhaps in the form of a kit together with a GTM900-B module and the needed FFC jumper), either by having me produce a batch or producing one themselves. As I already said, if I were to produce these MMTB1 boards, the assembly labor will be the dominant cost component, so perhaps someone else could produce them cheaper. Hasta la Victoria, Siempre, Mychaela aka The Mother