EEVblog Electronics Community Forum
Electronics => Projects, Designs, and Technical Stuff => Topic started by: MadScientist on March 24, 2022, 02:14:56 pm
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I’m looking for a system that allows me to place the SIM card remotely to the gsm router , I was thinking about designing an “ extender “
The required distance would be about 6 metres
I was wondering what the challenges would it entail , are there fast clocks used in SIM card interfaces , would it be possible to use a micro controller at each end to serialise the signals and then reconstruct etc. The other idea is just to use differential drivers to feed each signal
Thanks for your thoughts
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It looks like 1-5MHz so may depend on the device (router).
https://6point6.co.uk/insights/telecoms-stack-sim-cards/ (https://6point6.co.uk/insights/telecoms-stack-sim-cards/)
https://www.etsi.org/deliver/etsi_ts/102200_102299/102221/03.05.00_60/ts_102221v030500p.pdf (https://www.etsi.org/deliver/etsi_ts/102200_102299/102221/03.05.00_60/ts_102221v030500p.pdf)
Why do you need to extend the SIM 6m? Why not move the router itself?
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1-5Mhz with a relatively simple electrical interface?
https://en.wikipedia.org/wiki/ISO/IEC_7816#7816-2:_Cards_with_contacts_%E2%80%94_Dimensions_and_location_of_the_contacts
I'd be looking into whether an i2c extender could be made to cooperate.
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It looks like 1-5MHz so may depend on the device (router).
https://6point6.co.uk/insights/telecoms-stack-sim-cards/ (https://6point6.co.uk/insights/telecoms-stack-sim-cards/)
https://www.etsi.org/deliver/etsi_ts/102200_102299/102221/03.05.00_60/ts_102221v030500p.pdf (https://www.etsi.org/deliver/etsi_ts/102200_102299/102221/03.05.00_60/ts_102221v030500p.pdf)
Why do you need to extend the SIM 6m? Why not move the router itself?
For various reasons of coverage the unit is 4m high on top of a pole
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1-5Mhz with a relatively simple electrical interface?
https://en.wikipedia.org/wiki/ISO/IEC_7816#7816-2:_Cards_with_contacts_%E2%80%94_Dimensions_and_location_of_the_contacts
I'd be looking into whether an i2c extender could be made to cooperate.
TI do some nice high speed differential line drivers. The main issue being the bidirectional IO line. Afaik it’s simply the two data lines CLK and IO that present any technical challenge , this would mostly arise from clock skew imho.
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I think that such distance would be hard to implement. Cheaply. It all depends what you want to do,.
There are companies providing a SIM over ethernet, where you can via API select what kind of SIM would you like (from your pool). But it is expensive.
If you would like to switch between few SIMs then you can design a SIM multiplex circuit (with e.g. TXS02326a).
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Wouldn't it be easier to use a router with facility for an external antenna and mount just the antenna at the top of the pole? OK, you will get a little bit of coax loss but would be MUCH less hassle!
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I think the problem is that any buffering will need to know the data direction - AFAIK all comms is on a single bidirectional pin.
Using a router with an external antenna would seem to be the simplest solution - you lose a little signal on the cable but if that's make-or-break the whole setup is likely to be marginal even with the router at the top
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Due to the bidirectional nature you will likely have to emulate a SIM card in a MCU or something. Quite a bit of work for just putting a sim card in a more accessible spot.
If you are going to be hacking this router anyway it is easier to rip out the internal antenna and replace it with a SMA connector. That way you only need a passive antenna up there exposed to the weather. Making it easy to not only replace the sim card but even the entire modem if needed. But what if you have a fancy modem with a big MIMO phased array any everything? Just tap off one of those and it will use it. A directional antenna aimed at the cell tower of choice is going to have a much better signal than whatever phased array crap they can do in there.
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True about external antennas. But a secondary issue is the ability to switch sims easily. The idea was a panel mounted SIM “ drawer “ where a sim could be easily swapped. The router sim access is awkward at the best times
Looking at the interface the main issue is the bidirectional nature of the IO signal line. Since I don’t have a line turnaround signal I have to look how this might be done. Wired OR could be used
No modicfication to the router is expected. The sim just being replaced with a sim ribbon cable to the line driver board mounted outside the router
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Would a Season Interface as used in the past to hack PayTV work?
https://www.pulsat.com/products/Season-2-Interface-Logger.html (https://www.pulsat.com/products/Season-2-Interface-Logger.html)
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Just out of curiosity, why do you need to replace the SIM so frequently? Normally you stick the SIM in the device and unless you switch service providers you never have to touch it again...
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True about external antennas. But a secondary issue is the ability to switch sims easily. The idea was a panel mounted SIM “ drawer “ where a sim could be easily swapped. The router sim access is awkward at the best times
Looking at the interface the main issue is the bidirectional nature of the IO signal line. Since I don’t have a line turnaround signal I have to look how this might be done. Wired OR could be used
No modicfication to the router is expected. The sim just being replaced with a sim ribbon cable to the line driver board mounted outside the router
Then make a short adapter and stick it on top of the router in addition to extending the antenna. No need for line drivers.
https://www.datapro.net/products/panel-mount-dual-sim-card-extension.html (https://www.datapro.net/products/panel-mount-dual-sim-card-extension.html)
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Because as I sail from country to country I typically change the sim.