June 2005, Issue 179

Accurate Capacitance Meter
Cypress PSoC High Integration Challenge 2004 Contest Winner

EXTERNAL HARDWARE

You can implement, as a proof of concept, a capacitance meter with the CY8C27443 using just one external resistor, but a real application requires stability, a good power source, and, of course, a visual reading. A standard DC or AC power adapter powers the meter. A linear voltage regulator (LM317) generates V_DD. A MAX232 converts between CMOS and RS-232 levels on a standard DE9 male connector. A simple LC filter powers the MAX232 to suppress its noise. A standard 2 × 16 LCD generates alphanumeric output. A two-color LED from the starter kit indicates the measurement state. A pair of 75-W reference resistors connected in series is used as R_SET.