temperature-logger

Log ambient temperature readings in degrees Celsius and Fahrenheit.

Motivation: The ideal temperature while sleeping is between 60 and 67 degrees Fahrenheit. I am using this application to experimentally tune my heating systems (heater or thermostat settings) to the sweet spot. Of course, this application can be used for many other use cases where temperature logging is desired.

Usage

# in the project root folder
cd temperature_logger_umbrella/

# start elixir application
iex -S mix

# In another terminal start a tcp client
telnet 127.0.0.1 4040

# display available ports
> enumerate

# start logging with default period and file path
> start

# stop logging
> stop

# start logging every 60 seconds to the default file
> start 60

> stop

# start logging every 20 seconds to the file `~/logs/temperature.log`
> start 20 ~/logs/temperature.log

TCP Client API

enumerate

Prints out the available ports.

start <period> <path>

Starts logging temperature data.

Option	Description	Default
period	How often a sample should be recorded, in seconds (minimum is 1)	1
log_path	The path to the file that is written to	/temperature_logger_umbrella/log/temperature_logger.log

stop

Stops logging temperature data.

Installation

git clone git@github.com:johnc219/temperature-logger.git

Hardware

Required parts:

• TI MSP430G2553 microcontroller with Launchpad
• TMP36 temperature sensor
• .1uF capacitor (see TMP36 datasheet Basic Temperature Sensor Connections)

Note the 0.1 μF bypass capacitor on the input. This capacitor should be a ceramic type, have very short leads (surface-mount is preferable), and be located as close as possible in physical proximity to the temperature sensor supply pin. Because these temperature sensors operate on very little supply current and may be exposed to very hostile electrical environments, it is important to minimize the effects of radio frequency interference (RFI) on these devices.

Firmware

1. Install Energia
2. Ensure the MSP430G2 drivers are installed
3. Open temperature_sensor.ino
4. Connect the Launchpad via USB
5. Select MSP430g2553 under Tools > Board, and select the correct serial port under Tools > Serial Port. If you don’t see a selectable serial port, you likely have a driver issue.
6. Upload temperature_sensor.ino to the MSP430G2553

Software

1. Ensure elixir is installed
2. Ensure C compiler dependencies are satisfied
3. Navigate to temperature_logger_umbrella/
4. Run mix deps.get
5. Run mix compile

Extending to different boards

If you are using a board other than the MSP430, you can implement your own microcontroller code. The Elixir app expects to receive UART messages every second. The message is expected to be a JSON string with a \n at the end in the following format:

{ "celsius": <Number>, "fahrenheit": <Number> }

The code must adhere to the following rules:

• Baudrate of 9600 b/s
• Must start sending data when an "O" is received
• Must stop sending data when an "F" is received
• When sending, data must be sent at a period of 1 sec
• The data must be sent in format described above

Caveat

There is no current option to specify the port in the TCP client API. You must invoke

TemperatureLogger.start_logging(TemperatureLogger, [port: <String>])

directly in iex.

Q&A

Why not just buy a thermometer?

This application is to automate logging temperatures in addition to reading them.