Simple Signal Generator
A signal generator is one of a class of electronic devices that generates electrical signals with set properties of amplitude, frequency, and wave shape. These generated signals are used as a stimulus for electronic measurements, typically used in designing, testing, troubleshooting, and repairing electronic or electroacoustic devices, though it often has artistic uses as well.
This signal generator provides a 440 Hz sine wave output at two levels. The power supply may be 1.5-16V, so even a single 1.5 V battery can do. Opamp IC operates as a rectangular-wave generator; the values of R4 and C1 determine the frequency at which the output of the device toggles. Preset P1 enables the output to be set as a square wave (it may be adjusted by listening for minimum distortion). Network R5-R6-C2 reduces the output of-IC-1a by 3 dB (50%), after which the signal is superimposed on half the supply voltage (derived from the average level of the rectangular signal by C2). This voltage is needed for setting the DC operating point of IC-1b. Opamp IC-1b forms a third-order Chebishev filter with a cut-off frequency of 400 Hz, This filter removes the majority of harmonics from the rectangular signal so that the output is a reasonably clean sine wave. The level of the output signal is selected with S1 from potential divider R9-R10-R11, depending on the requirements of the circuit on the test. With a power supply of I 6 V, the output level is 1.5 V r.m.s. or 30 mV r.m.s., with a 1.5 V supply, the output levels are 150 mV and 3 mV. The output frequency is somewhat dependent on the supply voltage and varies from about 440 Hz at 16 V to around 370 Hz at 1.5 V. The circuit draws a current of 300 µA at 16 V and 80 µA at 1.5 V