SMS Controlled Switch using a raspberry pi

This code interacts with a SIM7600 4g module using AT commands over the serial port. It uses the module to send and receive text messages for the purpose of controlling one more more switches. I use this to turn a preheater on and off for my airplane, but it probably has other uses too :-) It started out for a SIM900 module which stopped working when TMobile shut down their 2g network. The AT commands are pretty much the same for both though.

Setup

On a raspian minimal image, install the following modules:

apt install python3
apt install python3-serial
apt install python3-rpi.gpio

If you want a 1-wire temp sensor to be detected, add the following lines to /etc/modules

w1-gpio
w1-therm

Commands

Commands are not case sensitive.

1. On Command

• Syntax:
  On <switchID> <time> <duration>
  Description: Schedules <switchID> to turn on in the future at <time> for <duration> minutes.

  Example:
  On 1 18:30 15
  (Turns switch 1 on at 18:30 for 15 minutes.)

• Syntax:
  On <switchID> <duration>
  Description: Turns <switchID> on immediately for <duration> minutes.

  Example:
  On 2 10
  (Turns switch 2 on now for 10 minutes.)

2. Off Command

• Syntax:
  Off <switchID>
  Description: Turns <switchID> off.

  Example:
  Off 1
  (Turns switch 1 off.)

• Syntax:
  Off
  Description: Turns off all switches.

3. Status Command

• Syntax:
  status
  Description: Returns the status of the switches, including whether they are on or scheduled to turn on.

4. Received Signal Strength Indication

• Syntax:
  rssi
  Description: Returns the signal strength as reported by the cellular modem.

5. System Info

• Syntax:
  system
  Description: Returns system info such as uptime and CPU temp.

4. Temp Command

• Syntax:
  temp
  Description: Returns the current temperature as measured by the external DS18B probe.

Configuring the SIM7600 to connect to the internet

Create the following file: /etc/ppp/peers/provider

# This is the default configuration used by pon(1) and poff(1).
# See the manual page pppd(8) for information on all the options.

# Do not ask the remote to authenticate.
noauth

# Serial device to which the modem is connected.
/dev/ttyUSB2

# Speed of the serial line.
115200

# Use this connection as the default route.
defaultroute

# Makes pppd "dial again" when the connection is lost.
persist

nocrtscts
debug
nodetach
ipcp-accept-local
ipcp-accept-remote
usepeerdns

connect "/usr/sbin/chat -s -v -f /etc/chatscripts/gprs -T fast.t-mobile.com"

Create the following file: /etc/systemd/system/ppp0.service to start the connection automatically on boot.

[Unit]
Description=PPP Connection
After=network.target 

[Service]
ExecStartPre=/bin/bash -c 'while [ ! -e /dev/ttyUSB2 ]; do sleep 60; done'
ExecStart=/usr/bin/pon
ExecStop=/usr/bin/poff
Restart=always
RestartSec=30
User=root

[Install]
WantedBy=multi-user.target

And then enable/start the service:

systemctl enable ppp0
systemctl start ppp0