Posted on Feb 5, 2014

This project demonstrates a number of aspects of the PIC16F687 microcontroller, like: ultra low power wake up, serial communications, nanowatt technology etc. The device can be used for different purposes. For example: measuring the content of a rain water tank, of a water tank in a motor home or trailer, and so on. Place the sensor wires in the t

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ank. After putting the batteries, you should see the content on the bar-graph display (between 1/8 and 8/8). After about a minute the display will switch itself off. You can switch back on again at any time by shortly pressing the button. To switch back off, press and hold the button for more than 1 second. Once an hour the display will put itself on for a few seconds, while this is happening the device will also transmit the measured value using RF (433. 92 MHz) (optionally). The transmitter/measuring module can be used by itself or in combination with an optional receiver module (wich operates on 230 VAC). This receiver module can be placed in a radius of 30 meter around the transmitter/measuring module. Diode D2 is for protection against reverse polarity of the batteries and also for lowering down the supply voltage somewhat. Two lithium batteries are supposed to deliver 6 volts, but in reality this will be about 6. 2 volts with new batteries, the voltage drop over the diode will bring this voltage down to about 5. 7 volts which is acceptable for the PIC and the other chips. So we don`t need to use a voltage regulator IC (which would consume more power). Because measuring fluids with the aid of DC current will lead to electrolytic effects and corrosion problems, in this device we will use a measuring current consisting of an AC block wave with a frequency of about 10 kHz. The circuit`s main purpose is measuring the level...

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