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Autoranging Capacitance Meter

wide-range, PIC-controlled

Autoranging Capacitance Meter
Most commercial digital Capacitance meters can measure capacitors from a few pFs (picofarads) up to 2,000 µF (microfarads). A few are able to measure up to 20 mF. Circuits like audio power amplifiers, switchedmode power supplies, printers and photocopiers often incorporate really large capacitors in the hundreds of mF range (1 mF = 1,000 µF). With this cheap circuit, you’ll be able to measure any capacitors of almost any ‘size’, from picos to Farads.Main Features– Low cost, direct reading,– Wide range, (from a few pFs up to several Farads)– Auto-ranging, (no range switches)– Auto-zeroing, (nulls stray capacitance of connected test leads or test jig on power up)– Low-Battery indication– Simple setup
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Gerber file

CAM/CAD data for the PCB referred to in this article is available as a Gerber file. Elektor 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.

Extra info, Update
The parts list and the circuit diagram indicate different transistors in position T1. Both the BC559B and the BC557B will work in this circuit, although the BC559B is the preferred device. The Farnell order code for the Pactec case used in this project should be: 736-442.
Resistors:
R1 = 120?
R2 = 5k?6
R3 = 5M?6
R4 = 1k?
R5 = 39k?
R6 = 10k?
R7 = 470? 1W (see text)
P1 = 1M? 10-turn multiturn preset, vertical mounting
P2 = 1k? 10-turn multiturn preset, vertical mounting
P3 = 100? 10-turn multiturn preset, vertical mounting
P4 = 22k?
Capacitors:
C1 = 47nF
C2,C7 = 100nF
C3,C4 = 4pF7
C5,C6 = 330nF
Semiconductors:
D1 = zener diode 5V6 1W
D2,D3 = 1N4148
IC1 = TLC555 (Texas Instruments), 3V555 or TS555 (Thomson)
IC2 = PIC16F84A-20/P, programmed, order code 020144-41
IC3 = 78L05
T1 = BC559B
Miscellaneous:
BT1 = 9V PP3 (6F22) battery with clip-on connector
JP1 = 2-way pinheader with jumper
K1 = two 7-way socket strips, lead pitch 0.1 inch
K2 = 16-way boxheader
K3 = PCB solder terminals
S1 = on/off switch
X1 = 20MHz quartz crystal
LCD display, 2x16 characters, e.g., Trimods 1536, Farnell # 142-554
Length of 16-way flat cable with IDC socket
Enclosure: e.g., Pactec HPS and HPLS series, type HPS-9VB (28x53x91x146 mm), Farnell # 736-351, see also www.pactecenclosures.com
PCB, order code 020144-1
Disk, source code and hex files, order code 020144-11 or Free Download
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