Comments on: Guide to SIM900 GSM GPRS Shield with Arduino

By: ABIY

ABIY — Sun, 12 May 2024 01:39:42 +0000

In reply to Sara Santos. Dear Sra Santos, When I enter AT command, I do not get any response. So please help me.

By: vht Vicky

vht Vicky — Mon, 11 Mar 2024 14:37:04 +0000

Hello, Is it possible to separate the message content and the number from the received message inorder to handle them differently?

By: Csabo

Csabo — Sat, 07 Oct 2023 17:27:05 +0000

By following your tutorial, sending SMS, initiating phone calls are working. My issue is that once the module receive an incoming call, it automatically hang up. There is no “RING” in the serial. Do you know what could be the problem? Wiring are the same, except that i don’t have FTDI programmer.

By: Xelula

Xelula — Wed, 05 Jul 2023 08:06:10 +0000

Excelent..!

By: vagelis

vagelis — Fri, 09 Jun 2023 08:28:02 +0000

very good work. but how can we recognize an incoming phone number so that if a known number calls us, some function will be activated

By: Noel

Noel — Wed, 01 Mar 2023 11:02:31 +0000

It is worth pointing out a couple of things:-
There are a number of these boards fitted with a SIM900A instead of a SIM900 main chip. This is obvious when you look at the board, or actual photos and not old ‘stock’ photos from internet suppliers. The difference is that the SIM900A is ‘Dual Band’ and not ‘Quad Band’. I have several boards and one is the SIM900A version will not connect for me, despite using SIMs that work in the other boards.
There is also a slightly smaller version of this board without the bulk of the battery holder and SIM carrier on the back. They also don’t have the phone jacks and RTC chip. The lack of an RTC is not really an issue, as the time can be picked up from incoming call and message activity.
Good luck with your projects….

By: Carlos

Carlos — Tue, 28 Feb 2023 17:25:06 +0000

I have a SIM900 I wanted a project that answers a call after 3 seconds, hangs up the call and activates pin 13 if the number is valid with a predefined list.

By: Noel

Noel — Wed, 01 Feb 2023 02:35:27 +0000

A quick follow up. I have had all sorts of issues with my UK network provider who I now refer to as VodaFoe – lol. I still can’t get credit onto a spare SIM, as suggested above to limit potential costs if things go wrong. However, the SIM has worked before and apart from not yet being able to send messages, it can still receive them for now.

I have fitted pin headers, 2 x 8 pin and 2 x 6 pin, to the underside of the empty ‘shield connectors’ – J13, J14, J21 & J22. I had previously swapped the existing yellow 6 pin headers out of J13 & J14 into J13_1 and J14_1. Fortunately I have a desoldering machine. This allows the UNO and SIM900 to fit onto a breadboard. The battery on the underside makes this a little tricky but it works. I also fitted pin headers to the other, empty spaces on the top of the board, 3 x 6 way and 2 x 5 way.

I found a good quality switch mode power unit from a discarded router at 5V 3Amps, the plug fits tight and it works well. However, I didn’t really want two power supplies for SIM900 and Arduino UNO. So rather than try to power the SIM900 off the Arduino, that I can understand is not wise, I have done it the other way around as the UNO needs much less current.

To keep connections simple, I have added a wire between the SIM900 DC Barrel Connector +ve on the back of the board, to connector J14_1 pin 6 ( NB not J14 pin 1 which is the connector beside it on the inner side of the two ). That is not connected to anything else on the SIM900 except J14 pin 1. This allows the UNO to get it’s power from the larger SIM900 PSU via its 3 Amp on board regulator. I fitted a Du Pont jumper wire between UNO 5V and SIM900 J14_1 pin 6 ( beside J14 pin 1 ). The regulator is running quite cool so far. No resets, glitches or data corruption encountered.

Initially, I could not get any intelligible characters in the serial monitor using the ‘Reading Received SMS’ code example above. Lots of funny characters that looked like a baud rate issue. I tried playing with Serial Monitor baud rates – no change. Then I spotted another, similar project, on another site, still using the SIM900 and UNO. They were using 9600 baud instead in their code. My board is brand new out of a sealed bag, so not sure why it is different, or why others are using different defaults. However, it now works perfectly after changing to 9600 baud in the code.

By: Noel

Noel — Tue, 31 Jan 2023 00:31:49 +0000

Thanks for the replies. I am more than happy that the UK regulator is giving my project a potential lifetime of a further 10 years. As it says, 3G can and will go, but 2G must remain for much longer. I quote below the relevant extract from that report :-

2G will be switched off by 2033

All the mobile providers have confirmed to the Government that they do not plan to offer their 2G (and 3G) services beyond 2033.

We expect that mobile providers will start making plans to switch off their 2G networks at some point after they have switched off their 3G networks. None of the providers have set a specific date yet, but we will update this advice if their plans change.

By: Ian

Ian — Mon, 30 Jan 2023 13:16:05 +0000

In reply to Noel.

Although in the UK, it’s the 3G they’re turning off and not the 2G. 2G is the GSM systems which runs your phone calls and SMS. If you turned 2G off completely then I think you’d have no phone service as that still runs on 2G. (3G/4G/5G are data only services in parallel to GSM).

As this shield is just 2G and if you’re only using it to send/receive SMS I think it will continue. If you’re using the data functions over 2G will then maybe they might somehow get disabled while still leaving SMS and phone service working. but then it’s probably not costing them anything to run that as it’s part of GSM anyway, which is still needed for the basic phone service.