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Re: Voltmeter + Ammeter LCD panel


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I think a common 1N4001 diode would work for both D1 and D2. 

Note that the full rectified voltage of the power supply enters D2 and goes to the 12V voltage regulators.  The upper limit of the voltage regulator is around 32v so there is a good possibility that the voltage being supplied is at the regulator's limit.      To correct this I added a 12V 5w zener diode  right after D2 to burn off 12V before it gets to the regulator.  This brings the voltage into  the 12V regulator well within its limits.  You will still need a heat sink for the 12V regulator.  The 5V regulator runs cool.

I initially used a 18V 5W zener but found it got quite hot and the 12V with heat sink was cool when using the fan.  Using the 12V zener balanced it out a bit.

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Hi BlAzink

pdo59 provided original Eagle files and code  for the 2 line display here  http://www.electronics-lab.com/forum/index.php?topic=12409.msg68409#msg68409  and http://www.electronics-lab.com/forum/index.php?topic=12409.msg68894#msg68894.    I used this to build the unit with some minor modifications. 
  I believe Pin 25 on the Atmega8 chip is not actually used  even though the sketch shows it connected to R1 and R2.  In simple terms I hooked up a wire from Point 13 on the original Power Supply sketch which is the wiper of P2, and connected it  to Pin 25.      The voltage  at Point 13 controls the allowable current for the powersupply.  I can vary it from 0-1.7v .  On my power supply I used a 0.27ohm resistor for R7 so using V=IR ,  V is read by the ADC and R is known so the program computes what current can be allowed based on the setting of P2 then send that value to the lcd.  By turning  P2 on the power supply (0 to 1.7v) the allowable current is computed and  displayed on the lcd.

For temperature, I used a 3 pin  temperature sensor such as a MCP9700a or a FM50??.    I ran a wire from the 5v regulator on the ammeter to power it.  One wire to the ground,  and the output wire goes to a ADC pin on the Atmega 8.

Then through much trial and error  I revised the code to read two additional ADC pins, calculate, and display the results. 

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