DS

The test beeper generates a sinusoidal signal with a frequency of 1,000 Hz, a common test  frequency for audio amplifiers.  It consists of a classical Wien- Bridge oscillator (also known as  a Wien-Robinson oscillator). The network that determines the  frequency consists here of a series connection of a resistor and  capacitor (R1/C1) and a parallel connection (R2/C2), where  the values of the resistors and  capacitors  are  equal  to  each  other. This network behaves, at  the oscillator frequency (1 kHz  in this case), as two pure resistors. The opamp (IC1) ensures  that the attenuation of the net- work  (3  times)  is  compensated  for.  In  principle  a  gain  of  3 times should have been sufficient to sustain the oscillation,  but  that  is  in  theory.  Because  of tolerances in the values, the  amplification ne...

As electrolytic capacitors age, their internal resistance, also known as "equivalent series resistance" (ESR), gradually increases. This can eventually lead to equipment failure. Using this design, you can measure the ESR of suspect capacitors as well as other small resistances. Basically, the circuit generates a low-voltage 100kHz test signal, which is applied to the capacitor via a pair of probes. An op amp then amplifies the voltage dropped across the capacitor’s series resistance and this can be displayed on a standard multimeter. In more detail, inverter IC1d is configured as a 200kHz oscillator. Its output drives a 4027 J-K flipflop, which divides the oscillator signal in half to ensure an equal mark/space ratio. Two elements of a 4066 quad bilateral switch (IC3c & IC3d) are alternately switched on by the complementary outputs of the J-K flipflop. One switch input (pin 11) is connected to +5V, whereas the other (pin 8) is connected to -5V. The outputs (pins 9 & ...