Capacitance Meter
using a CMOS timer
Published in issue 316, December 2002
As demonstrated in this article, a simple test instrument is sufficient to unravel the mysteries of the cryptic and impossibly small print often found on capacitors.Besides the obvious advantages of space savings, the miniaturisation of electronic components has a couple of dark sides too. Until about ten years ago, there used to be plenty of room on capacitor bodies to print the capacitance value, the tolerance, operating voltage, manufacturer code and other salient information. Today’s capacitors, being much smaller in size, have illegible, incredibly small and cryptic print on them and before fitting such a capacitor you are well advised to measure the actual capacitance! Rocket science? Well, no. The good news is that this article describes a low-cost and extremely simple instrument to do just that.
Resistors:
R1 = 390Ω
R2 = 22MΩ
R3 = 2MΩ2
R4 = 220kΩ
R5,R9 = 22kΩ
R6 = 2kΩ2
R7 = 220Ω
R8 = 1kΩ
P1 = 2MΩ5 preset
P2 = 25kΩ preset
Capacitors:
C1,C2,C4 = 100nF
C3 = 10µF 63V radial
C5 = 47µF 16V radial
Semiconductors:
D1,D3 = zener diode 5V6, 500mW
D2 = LED, red, high-efficiency (2mA)
T1 = BF245A or BF256A
IC1,IC2 = 555C or TLC555 (CMOS 555)
Miscellaneous:
S1 = rotary switch, 2 poles, 6 positions
S2 = pushbutton, 1 make contact
K1,K2 = 4-way SIL socket for IC pins, turned pins
Case, 60 x 10 x 126 mm with battery compartment
Knob
Moving coil meter, f.s.d.100 µA
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Click below to download a PDF copy of this article from Elektor magazine. Please note. In view of the complexity of international markets, Elektor cannot guarantee the availability of components for this project.
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