The 10€ LTE module A7670C: A review (and guide-ish thing)

This article is part of a series on the cheapest LTE modules of AliExpress. Please Donate to keep this series alive.

The appeal

The A7670C is extremely cheap. While it is not the cheapest I have ever seen, it is quite impressively cheap. It clocks in at 9.34€ for a pre-assembled board WITH external antenna, and 9.86€ for the bigger board.

I bought the smaller board because I do not need the extra pins of the big one.

Specs

GSM and voice calling available in some listings, but not in the one I bought.
LTE CAT.1 speeds, that is 10 megabits down and 5 megabits up; (GSM EDGE, that is 236.8 kilobits both down and up)
TCP, UDP, HTTP, FTP, HTTPS, FTPS, MQTT support builtin
Transparent transmission supported (default mode: command)
Over-the-air firmware upgrade
USB support
SMS, but not necessarily voice (if voice is available, so are Text-to-speech and Voice replay)
Bands: LTE-FDD B1, B3, B5, B8; LTE-TDD B34, B38, B39, B40, B41; (GSM 900, 1800)
Frequencies: LTE-FDD 2100, 1800, 850, 900; LTE-TDD 2000, 2600, 1900, 2300, 2500; (GSM 900, 1800)
This places it in slightly problematic territory for worldwide use as TDD bands are only usable an china, and not enough FDD ones are supported for good global reception.

Compatibility with western networks

I live in germany, and tested out two SIMs so far: One from the Telekom (D1 network), and one from 1und1 (EPlus network). Most FDD bands are deployed in europe (and one TDD band: B38). In germany itself however, only the B1, B3, and B8 bands are deployed (plus others this module can't access anyway). They're deployed by ALL carriers, but with different coverages.

Both SIMs were usable as this one's transceiver is much cleaner than that of the last one.

Let's plug it in

Upon connecting the module's VIN pin to 5V, and connecting its UART to my PC on 3.3V level, I was immediately able to send commands to it. It was not only very quick to react, but also very nicely documented online. But wait, there's more! The AT commands are almost entirely compatible with the other SIMcom LTE modules, so a tutorial for the A7600E for example, works for this one too!

I'm immediately very glad to see how easy this one is to get running, unlike the FS800E from the last article.

Using it

Now since it works so well, I think this deserves a little getting-started guide right now, right here! So, I'm simply using a USB-to-UART adapter thing, set to 115200 8N1. An arduino as a "serial proxy" would work for this too.

The setup on the PC: Open the arduino IDE, select the module's serial port, open the serial monitor. Line endings: CRLF

19:10:13.683 -> 
19:10:13.683 -> *ATREADY: 1
19:10:17.688 -> 
19:10:17.688 -> +CPIN: READY
19:10:19.310 -> 
19:10:19.310 -> SMS DONE
19:10:19.376 -> 
19:10:19.376 -> +CGEV: EPS PDN ACT 1
19:10:20.671 -> 
> AT+CREG?
19:10:20.671 -> AT+CREG?
19:11:07.504 -> +CREG: 0,1
19:11:07.504 -> 
19:11:07.504 -> OK
# Let's send an SMS first! These commands are identical to those of the SIM800L module.
> AT+CMGF=1
19:13:30.004 -> AT+CMGF=1
19:13:30.037 -> OK
> AT+CMGS="+49MYNUMBER"
19:13:53.979 -> AT+CMGS="+49MYNUMBER"
19:13:53.979 -> > 
> Hello[[paste \x1A here]]
19:15:03.182 -> Hello
19:15:03.347 -> 
19:15:03.347 -> +CMGS: 243
19:15:03.347 -> 
19:15:03.347 -> OK
# I received the SMS as expected!
# Now let's do internet!
> AT+CGDCONT=1,IP,"internet.telekom"
19:23:24.244 -> AT+CGDCONT=1,IP,"internet.telekom"
19:23:24.244 -> OK
> AT+CIPMODE=1
19:24:53.526 -> AT+CIPMODE=1
19:24:53.526 -> OK
> AT+NETOPEN
19:25:15.539 -> AT+NETOPEN
19:25:15.539 -> OK
19:25:15.539 -> 
19:25:15.539 -> +NETOPEN: 0
> AT+CIPOPEN=0,"TCP","tudbut.de",81
20:01:55.353 -> AT+CIPOPEN=0,"TCP","tudbut.de",81
20:01:55.486 -> CONNECT 115200
> GET /hello_world.txt HTTP/1.1
> Host: tudbut.de
> 
20:03:00.946 -> HTTP/1.1 200 OK
20:03:00.946 -> Server: nginx/1.14.2
20:03:00.946 -> Date: Sat, 30 Sep 2023 18:03:00 GMT
20:03:00.946 -> Content-Type: text/plain
20:03:00.946 -> Content-Length: 8
20:03:00.946 -> Last-Modified: Sat, 30 Sep 2023 17:26:36 GMT
20:03:00.946 -> Connection: keep-alive
20:03:00.946 -> ETag: "65185a4c-8"
20:03:00.946 -> Accept-Ranges: bytes
20:03:00.946 -> 
20:03:00.946 -> hiiiiii
# turn line endings off
> +++
20:03:18.956 -> 
20:03:18.956 -> OK
# turn line endings back on
> AT+CIPCLOSE=0
20:03:26.565 -> AT+CIPCLOSE=0
20:03:34.283 -> OK
20:03:34.283 -> 
20:03:34.283 -> CLOSED
20:03:34.283 -> 
20:03:34.283 -> +CIPCLOSE: 0,0
# delightful!
> AT+CPOF
20:05:25.869 -> AT+CPOF
20:05:25.869 -> OK
20:05:26.166 -> 
20:05:26.166 -> +CGEV: NW PDN DEACT 1
20:05:26.166 -> 
20:05:26.166 -> +CGEV: ME DETACH
20:05:26.166 -> 
20:05:26.166 -> +CIPEVENT: NETWORK CLOSED UNEXPECTEDLY

As you can see by the timestamps, it took weirdly long for me to do all this. Well, that's because I wrote things down as I was learning them. :P

Conclusion

Unlike the FS800E, this does everything it promises to do, and if you're lucky enough not to get the LANV variant, it might even do GSM and phone calls! But even if not, this module is so worth it. Especially considering the similarities with other SIMcom ones, because that allows us to use code written for the more expensive modules on this really cheap one.

Here's where I bought it from

However, one issue: The title clearly states it does GSM, but it does not do that. I have messaged the seller about this and have told them to update the title or start shipping correctly. We'll see how that turns out.

Once again, please Donate to keep this series alive (and so that the two FS800E purchases for absolutely nothing are less painful lol).