Introduction

Pictured above is a Raspberry Pi Model 4b (L) connected to an SIM800C module (R) to send and receive Short Messaging Service (SMS) Cellular phone messages commonly referred to as “Texting”. This device has possible applications for Emergency Management organizations where Response Teams can be alerted or updated with timely information and instructions.

Hardware Description

The Raspberry Pi Model 4b is a computing platform featuring a high-performance 64-bit quad-core processor, dual-display support at resolutions up to 4K via a pair of micro HDMI ports, hardware video decode at up to 4Kp60, up to 8GB of RAM, dual-band 2.4/5.0 GHz wireless LAN, Bluetooth 5.0, Gigabit Ethernet, USB 3.0. Only a small portion of the features is required to rapidly send lists of names, phone numbers and text messages to the SIM800C module. Cost is about $80, including heatsink as shown.

The SIM800C module from SIMCom is a Quad-band GSM/GPRS Module that operates in the 850/900/1800/1900 MHz bands for voice, SMS, and data information. It delivers a data rate of 85.6 kbps and supports CS 1, 2, 3, and 4 coding schemes. This module also supports point-to-point MO & MT, SMS cell broadcast, and text & PDU modes for SMS. Total cost is about $10 on eBay.

Software Description

A #! /bin/bash shell script takes command line arguments for a text message (*.txt file) and a contact list (Name, Phone #) in CSV format. Iterating through the contact list, commands are sent through the system’s minicom modem program to the SIM800C module. The result of each call is logged to a file. This bash shell script was mainly written by ChatGPT.

Note that a single SMS message is defined as alphanumeric characters only with a maximum length of 160 characters (including spaces). Smartphone designers add features to handle longer messages, perhaps containing emojis and graphic files.

SIM Card

A cellular SIM card is required to connect to the cellular network. I chose UltraMobile who offer low cost, pay-as-you-go plans for Data, Text, Voice access. Monthly Rate is $3, Unlimited 1-day data Pass (including SMS) is $5.

Reference Links

Raspberry Pi 4B product description: raspberry-pi-4-product-brief.pdf (raspberrypi.com)

SIM800C Module Datasheet: SIM800C (simcom.com)

UltraMobile SIM Card: https://ultramobile.com

SMS message guide: https://www.androidpolice.com/sms-guide/

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