Oldschool SMS gate - own construction

[Vermes]

It is a device for sending and receiving short text messages.
The SMS gate consists of three main elements:

• GSM modem
• computer
• user's console
• cables, wires and universal plate

Well known and rather disliked Chinese ZTE MG3030 module (soldered in the universal plate in next photo) acts as the GSM modem. It supports all the normal AT commands for GSM modems, therefore it is not necessary to use the documentation provided by manufacturer. On the one side it is connected to the antenna, on the other it is connected to the microcontroller by UART. The third side is connected to the SIM card.



The microcontroller is STM32F103 (32-bit core Cortex M3, working with frequency of 64MHz, 20 KB RAM, 128 KB Flash). There are only few accompanying electronics: the relay which activates the power of console, two LEDs, few transistors that support transmission in the loop and the power supply.
The user's console is ASR33 teletype made in U.S. The encoding and decoding data transmitted in series, 1 start bit, 8 data, 1 stop, using the loop, is done mechanically.
The aim of this project was to make no modifications to the teletype. Some cables were attached to the terminal panel on the back of the device.
Photo below shows the partially disassembled for maintenance 'distributor' – a shift register producing serial data.



The software was self written. It uses a multithreaded 'operating system' Free-RTOS.
User, beyond the possibility of sending and receiving SMS, has access to a phone book (with the possibility of editing entries) and some functions such as checking the signal strength.
In the picture – a piece of teletype print.



The last picture – electronics built in teletype's 'leg'. The big transformer gives 115V to the teletype. It is a small toroid.




Link to original thread (video) – Oldschoolowa bramka SMS