three digit display.

  
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The Mini 3 digit display aka `DVM-module` (digital voltmeter module) can easily be tuned and modified because you have control over the firmware. The key advantages of this module are: The internal reference voltage in the atmega8 microcontroller is 2. 56V. Just by adding 2 resistors one can measure any voltage higher than 2. 56V. How can I measure
three digit display. - schematic

smaller voltages It`s simple: just add an amplifier. The problem is only the power of supply for the amplifier circuit. A lot operational amplifiers need positive and negative voltages of e. g +/- 15V. That is not really convenient for our application. We need something that works with about 5V (same as the atmega8). The TS272 or TLC272 is a very good option. It has a very high input impedance of typically 1GOhm. You can use this therefore for true voltage measurements e. g on electrochemical cells. The combination of resistors in the above example gives you a measurement range from 0-500mV with 1mV resolution. VDIV has to be adjusted in the file analog. c to calibrate the amplification factor into the software: Note that a voltmeter with more than 1GOhm input impedance is very sensitive to electric fields and grabs any voltage just out of the air. I recommend to use a shielded cable or to lower the input impedance by adding a resistor in parallel to the input (Ri in the above schematic). To measure a current you just need to measure the voltage over a low ohm resistor (e. g 1 Ohm, 5W). A current of 2A would then result in a voltage drop of 2V. By changing the VDIV calibration constant in the file analog. c you can calibrate the circuit as needed. If a voltage drop of 2V is not acceptable then just use 0. 1 Ohm and add an amplifier. You can then adjust it to your needs by using the above amplifier circuit with a different...



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