Remote SIM interface  - Page 1
Forum section: electronics / projects

author: MadScientist
author_rank: Frequent Contributor
timestamp: March 24, 2022, 02:14:56 pm
content: 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 metresI 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 signalThanks for your thoughts

author: thm_w
author_rank: Super Contributor
timestamp: March 24, 2022, 11:01:38 pm
content: It looks like 1-5MHz so may depend on the device (router).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.pdfWhy do you need to extend the SIM 6m? Why not move the router itself?

author: robzy
author_rank: Regular Contributor
timestamp: March 25, 2022, 03:55:45 am
content: 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_contactsI'd be looking into whether an i2c extender could be made to cooperate.

author: MadScientist
author_rank: Frequent Contributor
timestamp: March 25, 2022, 07:19:43 am
content: Quote from: thm_w on March 24, 2022, 11:01:38 pmFor various reasons of coverage the unit is 4m high on top of a pole

author: MadScientist
author_rank: Frequent Contributor
timestamp: March 25, 2022, 07:22:56 am
content: Quote from: robzy on March 25, 2022, 03:55:45 amTI 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.

author: MatjazB
author_rank: Newbie
timestamp: March 25, 2022, 08:08:33 am
content: 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).

author: nali
author_rank: Frequent Contributor
timestamp: March 25, 2022, 08:50:07 am
content: 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!

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: March 25, 2022, 09:17:51 am
content: 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

author: Berni
author_rank: Super Contributor
timestamp: March 25, 2022, 11:59:21 am
content: 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.

author: MadScientist
author_rank: Frequent Contributor
timestamp: March 25, 2022, 12:12:49 pm
content: 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 timesLooking 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 usedNo 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

author: Bicurico
author_rank: Super Contributor
timestamp: March 25, 2022, 05:37:13 pm
content: Would a Season Interface as used in the past to hack PayTV work?https://www.pulsat.com/products/Season-2-Interface-Logger.html

author: TheMG
author_rank: Frequent Contributor
timestamp: March 25, 2022, 06:28:32 pm
content: 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...

author: thm_w
author_rank: Super Contributor
timestamp: March 25, 2022, 10:10:20 pm
content: Quote from: MadScientist on March 25, 2022, 12:12:49 pmThen 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

author: MadScientist
author_rank: Frequent Contributor
timestamp: March 26, 2022, 10:47:34 am
content: Because as I sail from country to country I typically change the sim.