A few times a month I bring my old aunt to the local church. Sometimes the church service takes much longer time and the end time is hard to predict. So after a few half an hours waiting, I thought it would be better if she could warn me the service had ended. However, she is 88 years old and can not handle a regular smart phone anymore.
I got the idea to make a device so she can alarm me to pick her up, that way this quick project was born.
The module has only one switch, if you switch it on, it connects to the GSM network, gets the time from the network and sends a SMS: "your aunt wants to be picked up" together with the measured battery voltage and the time the SMS was send.
The device is made from:
Step 1: Flash the Sim900A
The stock sim900A does not work in my country (The Netherlands). However, after flashing it with the 1137B09SIM900B32_ST.cla firmware it works fine (you can even use a mobile data connection (GPRS).
The firmware is found on this website.
Flash via a FTDI adapter.
Step 2: Hardware Setup
Step 3: Software Setup
The code is published on my Github.
- An init of the GSM module
- Ensures a connection to the GSM network
- Gets the time from the GSM network
- Ensures the SMS was send (if the sending was not succesful, another attempt is made after 60 sec)
- Sets the GSM module to sleep to save battery power in the time before the module is switched of by me