The goal of this project was to build a small, cheap, light-weight telemetry transmitter to attach to a small animal. This version uses a commercial, low-power transmitter, the Radiotronix RCT-433-AS. The design worked well, but has a relatively high current draw of about 500 microamps. A CR1620 lithium coin cell runs the circuit for about a week. The current version uses a pair of CMOS oscillators to produce a chirp once per second.
The circuit shown above has two standard CMOS multivibrators. The second is gated by the first. The duty cycle of the first oscillator is about 1%, or 10 mSec every second. A logic-high at the telemetry transmitter control turns it on.
The circuit board was layed out using ExpressPCB software. You will need to download a copy to view the design file. The components are all surface mount. The dots shown below are on a 0.1 inch grid.
Note the antenna lead at the lower left. At 433 MHz (70 cm wavelength) a quaterwave antenna should be 17 cm long. The battery is partly shown at the right. It is a CR1620 lithium cell, but any 3 volt source may be used. The transmitter module sticks out to the left. Visit page
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