• RS232 Data Bus Status Indicator
  This circuit indicates TXD and RXD activity.  The thresholds are set at plus 3 volts and minus 3 volts. (added 12/04)

• RS232 Serial Interface Status Indicator
  I designed this circuit many years ago and have used it several times since.  It uses a single logic IC to indicate the TXD and RXD line activity of a typical RS-232 serial data communications link.  The thresholds are set at plus 3 volts and minus 3 volts.  Two dual color LEDs are used as indicator lights.

Revolution Meter:  Revolution meter by measuring method of strobe synchronization. It can measure up to 100,000 rpm in two ranges.  (added 6/06)

RF Power Meter #2:  (circuit / schematic added 2/03)

RF Power Meter for the QRPer:  (electronic design / schematic added 2/05)

RF Power Meter:  simple RF power meter cum dummy load for low power transmitters. . (added 9/04)

RF Probe:  Use this probe with any transmitter for tuning. Connect the probe at the output of each stage and tune till maximum DC voltage appear on Digital Voltmeter.  (added 11/05)

Ring oscillator measures cable length:  05/12/94 EDN Design Ideas  In Fig 1, an ECL exclusive-NOR gate (F100107) and a length of cable form a simple ring oscillator. The delay from the cable and the gate determine the ring oscillator’s frequency. A 100m cable yields approximately a 600-MHz oscillation frequency. The gate’s second output connects to a frequency counter.  (added 09/05)

RMS Calculations for Energy Meter Applications Using the ADE7756:  AN-578 Analog Devices Application Notes  (app note added 6/06)  The document describes the implementation of an rms signal processing algorithm using the ADE7756 and a Microcontroller (PIC16C63)   from Microchip.

RMS to DC Converter is Accurate and Stable:  09/14/95 EDN-Design Ideas / (added 11/05) Combining the well-known true RMS-to-dc circuit with a simple S/H circuit eliminates offset errors, which increases accuracy and temperature stability. The circuit in Fig 1 uses a low-cost analog multiplier, IC1; an integrator, IC3A, R5, and C1; and an analog inverter, IC2, R3, R4, and D1 to convert the analog VIN into a true-RMS dc VOUT. The input signal can be ac, dc, or a combination. With an input-signal range of 0 to 2V, the circuit can handle ac signals with crest factors up to 5. Unfortunately, offsets in IC1 and IC3A contribute significant error to the circuit. Moreover, these offsets drift with temperature. To remove these offset errors, the circuit performs self-calibration with the help....

RS-232C Link Monitors Animal Activity:  11/06/97 EDN-Design Ideas / (added 6/06)