User manual

depends on the operating voltage and is indicated in the data

sheet for the micro controller at Vcc x 0.7.

001 HIGH = 5V x 0,7

Before a HIGH level is recognised in the digital port, some time

will pass. We measure it within the Do-while-loop using the

variable

C_time

is approximately proportional to the

capacity of the capacitor, i.e. when

C_time

is very large, the

capacity to be measured is very large as well.

To get the proper measured value, we need to convert the variable

(

C_time

•

Factor

). The value (factor) must be determined ex-

perimentally with »a few calibration capacitors«, since

recognition of a HIGH level will deviate slightly from controller

to controller in spite of the information Vcc x 0.7 in the data

sheet, and the oscillator frequency of 16 MHz is not 100 % the

same in every board (quartz tolerances). Finally, the measured

value will be divided into Nanofarad (nF) and Mikrofarad (µF)

with a simple If()-query and output on the LCD before a new

measurement starts.

Get a few new capacitors – always use capacitors of which you

know precisely what capacity they have. You may have them

measured by an electronics specialist in the lab. New capacitors

usually have the printed-on values +/- 20 %, depending on type.