Op 2 februari 2009 13:59:57 schreef klein is fijn:
[...]Zo'n V/A meter met PIC/AVR vergt overgens wel wat serieus afregelwerk. Even de software van een andere site halen geeft enorme afwijkingen.
Volgens de handeling zit er een setup in, waar je max. voltage, max. spannig en vref. kan in stellen.
En voor die €5,00 wil ik het wel wagen
During normal work short S1 circuit cancel amount of displayed charge. In versions without charge displaying, short S1 circuit doesn't make any reaction.
To enter setup push and hold S1 switch (short S1 circuit), then power on multimeter. When "www.elfly.pl" appear on LCD, you are in setup mode.
First parameter to adjust is ATMega8 voltage reference. Reference voltage inaccurracy is the main measurement error factor in previous multimeter code versions, because Vref vary from chip to chip in quite wide range . You can measure reference voltage between multimeter ground and µC pin no. 21. There are special pads on PCB marked "Vref" to make it easily. Measured value you should write down in setup. If you don't write anything, it will be assumed, that Vref=2.56V (due to datasheet).
After Vref setup, button must not be pressed for about 5 seconds. The next parameter to set up is shunt resistor value.
If the resistor value is known, repeat button pushing until correct value reached. If resistor value is unknown (e.g. self made resistor), short PSU output by ammeter, set some current by PSU current limit regulator and then, push button, lead to equal current indication on ammeter and multimeter.
After shunt resistor value setup, button must not be pressed for about 5 seconds. The next parameter to set up is voltage.
Because PDIP version doesn't have potentiometer to adjust input voltage divider, you have to do it in soft manner. Simply connect voltmeter to PSU output and pushing S1 lead to equal voltage indication on ammeter and multimeter.
After voltage setup, button must not be pressed for about 5 seconds.
The next parameter to set up is fan switch-on power threshold. It is the real power loosed on output transistor (transistors), because multimeter has information on voltage drop on transistor and driving current. To avoid instability switch-off threshold is automatically set to 20% less than switch-on one.
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op 2 februari 2009 18:13:34