Thermo-Master

The hardware was constructed on a breadboard for testing, then the schematic was created in Eagle and a circuit board manufactured. All the ICs are surface mount devices.

Input power is provided from a ‘wall wart’-type adapter, providing 5 VDC through a standard 2.1mm DC plug. Voltage regulation is done by a MIC39100-3.3 regulator providing the +3.3 VDC to power all circuits.

The microcontroller is a Parallax P8X32A (Propeller) in the QFP surface-mount package, with the program stored in a 24LC512 Serial EEPROM. Pads are provided on the edge of the circuit board for programming the EEPROM.

The XBee Wireless RF module is mounted in the required 2mm sockets. It is an Xbee 2mW Series 2.5 Chip Antenna. When I purchased another unit recently for doing some breadboarding, I purchased this as Xbee 2mW PCB Antenna - Series 2 (ZigBee Mesh). The XBee was configured using the Digi X-CTU configuration software and set as ZNET 2.5 COORDINATOR AT.

A two-pin header provides a connection for the pushbutton (normally open) switch. The pushbutton switch input to the Propeller is pulled to ground via a 10K resistor, and goes high upon switch closure. The pin is current-limited via an inline resistor. A small tactile pushbutton is also soldered to the pcb which provides a RESET function for the microcontroller, when pushed.

The main program first initializes the communications (FullDuplexSerial4port), then inits the LCD display. The real-time clock (DS1307_RTCEngine) cog is started and the time is read and stored. Next, cogs are started that read the temperature/humidity (uses Sensirion_full), monitor XBee communications, monitor the pushbutton, and write to microSD (uses fsrw). The program then enters a loop that monitors various flags (SettingRTC, NewOutTemp, NewDwnTemp, NewLocTemp) and calls subroutines based on the state of the flags. It also updates the time display once a second.

This starts the cog for reading the SHT11, which then takes a reading from the sensor every 5 seconds. After storing the temp/humidity data, a flag ‘NewLocTemp’ is set, indicating to the main program loop that the LCD should be updated.

This cog monitors the XBee ‘receive’ line for incoming data. The incoming data is identified by the first character received:

First Char	Message
D	the transmission is from the downstairs XBee. The rest of the transmission is parsed and stored as the downstairs temperature and a flag is set ‘NewDwnTemp’ to indicate that the main loop needs to update the downstairs temperature displayed.

T	this is a request from the downstairs unit for the current date/time and outside temp. A function is called to send the requested data.

O	this is a transmission from the outside unit. The temperature and humidity are parsed from the data string and stored, and a flag set ‘NewOutTemp’ to indicate to the main loop that the outside information has updated. The upstairs temperature is sent to the downstairs unit before resuming.

When this cog is launched, it retrieves the date/time info and uses that information to produce a filename in the format "yy-mm-dd.csv". The microSD card is mounted and a file opened. A header indicating “=== REBOOT ===” is written before the standard data header. This indicator is only written at cog initialization and can be used to see that the system restarted for some reason. The cog then enters a loop monitoring the current date/time. On the quarter-hour, the drive is mounted and the current data is written to disk. Each midnight, a new file is opened for that day’s data collection. A data header is written at the top of each new file.

This cog runs in a loop waiting for a button press. When a button press is detected, the cog sets a flag ‘SettingRTC’ to indicate to the main loop that the time-setting function should be called. The time-set routine uses short button presses to increment the current variable (year, month, day, etc) and long button presses to indicate that the current data is correct and to move to the next variable (after setting year, moves to setting month, etc).

Thermo-Master v2.2