My final-year project was to add a few sensors to an ordinary coffee percolator. The heating element was controlled using an opto-coupled TRIAC as the actuator. This percolator is then remotely monitored via the Trinity SMART Sight service that transmits and receives instructions via a Sierra Wireless FXT009 GSM modem which has additional custom AWTDA commands to communicate with the Trinity SMART platform.
The microprocessor chosen for this project, because it had 16 ADC ports, which are handy when interfacing various sensors.
For this project it was required to measure the base, steam and coffee pot's temperature. The Microchip MCP9700 thermistors were used for measuring the base and steam temperatures, while the Melexis MLX90614 infrared themometer was used to measure the coffee pot's temperature.
This thermistor does not need extra conditioning circuitry. It is literary a ``plug-and-play'' thermistor. It is inexpensive (costs ZAR 3.50) and very durable for a TO-92 package (it can operate in temperatures ranging from -40°C to 125°C). Its accuracy is unfortunately +/- 2°C, but for the price one cannot complain.
The MLX90614 is an infrared thermometer for non-contact temperature measurements. It is factory calibrated for ambient temperatures within the range of -40°C and 125°C. It can also detect temperatures from objects within the range of -70°C and 382°C. The average temperature is calculated within the field-of-view of the sensor with a typical accuracy of +/-0.1°C. An optical filter (high-pass filter) that cuts off the visible and near infrared radiant flux is integrated in the package to provide ambient and sunlight immunity. The wavelengths that are allowed to pass through the optical filter ranges from 5.5 to 14 micrometers.
Where to buy?
- Sparkfun - Click here
- Netram.co.za - Click here
- Riektron - Click here
Very inexpensive and easy circuit to build.
Components used:
- Fairchild MOC3061 --- Opto-coupled TRIAC driver with built-in zero-crossing circuit (Buy) (Datasheet) (App note)
- NXP BT136-600E --- Main TRIAC (Buy) (More info)
- 2N2222 --- NPN Switching Transistor (Buy)
This Fairchild MOC3061 opto-coupled TRIAC is used, in conjunction with the BT136-600E TRIAC, to control the percolator using the cycle control method [1].
For measuring the water reservoir level, ultrasensors were used. An adapted version from this site was used for implementing this sensor.
- [1] ON Semiconductor. (2006, Nov) Thyristor Theory and Design Considerations. [Online]. Available: http://www.onsemi.com/pub_link/Collateral/HBD855-D.pdf
- [2] Philips Semiconductors, "Chapter 6 - Power Control with Thyristors and Triacs." [Online]. Available: http://www.nxp.com/documents/application_note/APPCHP6.pdf