About the article

Capacitance Meter

using a CMOS timer

Capacitance Meter
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.
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Gerber file

CAM/CAD data for the PCB referred to in this article is available as a Gerber file. Elektor GREEN and GOLD members can exclusively download these files for free as part of their membership. Gerber files allow a PCB to be produced on an appropriate device available locally, or through an online PCB manufacturing service.

Elektor recommends its business partner Eurocircuits as the company of choice for its own prototypes and volume production in selected cases.

Component list
R1 = 390?
R2 = 22M?
R3 = 2M?2
R4 = 220k?
R5,R9 = 22k?
R6 = 2k?2
R7 = 220?
R8 = 1k?
P1 = 2M?5 preset
P2 = 25k? preset
C1,C2,C4 = 100nF
C3 = 10µF 63V radial
C5 = 47µF 16V radial
D1,D3 = zener diode 5V6, 500mW
D2 = LED, red, high-efficiency (2mA)
T1 = BF245A or BF256A
IC1,IC2 = 555C or TLC555 (CMOS 555)
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
Moving coil meter, f.s.d.100 µA
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