Meter Tester This unit uses switches and resistors to provide a number of current ranges. It allows you to test most of the meters available at surplus outlets, and without damaging the sensitive movements when yo ... read more>>
Digital Tachometer Counter This circuit produces a readout for the digital tachometer circuit. IC9 is a 3-digit LED display driver, counter and latch. IC8 drives the common-cathode LEDs, which are enable by Q1, Q2, and Q3. See ... read more>>
AC Current Indicator Using a dual op amp driving a rectifier and emitter-follower, this circuit indicates ac current on an LED. L1 is an audio transformer winding using a pick-up coil, or 100 to 200 turns of #28 gauge wir ... read more>>
4 Range AC Millivoltmeter By placing the rectifier in the op amp feedback path, nonlinearity is greatly reduced to insignificant levels. The meter will read the full-wave rectified average (absolute value) of the input signal. ... read more>>
1-Khz Harmonic Distortion Meter The circuit useful for distortion measurements notches out the fundamental frequency of 1 kHz to allow measurement of the residual level of harmonics. First a true RMS meter is used to measure the 1-k ... read more>>
