Introduction
Building a telephone, how hard can it be?
Cost of project about 150 DKK, excluding trivial components also suitable for other projects (wires, swiches, regulators and such) and 19 DKK a moth for the phone plan.
Pictures and demo video
Important notes
The SIM800L module only supports 2G, so you need to use a provider, which offers 2G. Lebera does that and their cheapest plan is only 19 DKK a month, so they are perfect.
Components used
- Ardiono Nano
- SIM800L
- Microphone
- Speaker
- Amplifyer board
- 18650 Battery and insert
- Voltage regulators
- Push buttons
- On/off switch
- LED
- Resistors
- Wires
- Perf board
- Cardboard box
High level schematics
A single 18650 battery powers everything remenber common ground
Sim800L module is connected by RX and TX. Code is driven by AT-commands.
Push buttons are connected to the Arduino nano and trigger actions with AT-comamnds passed though RX TX, like dial mormor, dial farmor (mothers mother and fathers mother), hang up, send sms asking farmor, when we can eat pancakes.
The speaker is connected to Sim800L, but it needs to routed though an amplifyer board for proper sound.
Voltage regulator ensures that Sim800L can get steady 4v Very impotant and that the Arduino gets 5v.
The code is an event driven FSM by AT-commands triggered from push buttons.