Monday, October 13, 2014
DIY Digital Thermometer in Wireless Form Overview and explanation
Overview
This digital thermometer project uses any standard FM broadcast band radio at regular intervals in order to report the temperature.
Explanation
An Atmel AT90S1200 is used to construct the prototype along with a modified low cost wireless microphone kit that function as the transmitter in order to save design time. The device can be used as standalone or as part of a PC-based weather station or HVAC system since it uses a simple low bit rate tone signaling scheme which can be interpreted easily by both machines and humans. The design allows the use of any inexpensive FM radio to monitor the temperature with easy set up of any number of monitoring locations.
There are various circuits used in this project including, the thermometer interface, audio interface, and power interface. The operation consists of applying power and tuning the unit to any unused FM channel. A 9V transistor radio battery was chosen since the 5V regulator used can accept any DC voltage between 5.5V-12V. A programs tests if larger or lesser and converts the binary format temperature output from the thermometer clip to a format that can be transmitted a digit at a time.
Wednesday, September 24, 2014
Triangular wave form Generator Circuit
A suitable circuit is shown, it has the unusual advantage that only the one power supply is required. When the output voltage from the Schmitt trigger circuit is low, the current flowing through Ra is integrated by C; to produce the negative slope of the triangular wave at output 1. When the output 2 voltage from the Schmitt trigger ls high, current flows through R; to produce the rising part of the waveform at output 1. The output waveform will have good symmetry if R1 = ZR;. The output frequency ls given bythe equation: f=V(+) - Vbe/2R1C1V Whel8 R1 = 2Rg, V35 ii the steady voltage at the inverting input (0.5 V) and V is the difference between the tripping points of the Schmitt trigger.
