• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
Resource icon

Simple, cheap, Square/Triangle/Sine-wave generator 2012-05-25

A test signal generator is invaluable when making or repairing electronic equipment. Although a fully-fledged, accurate (and expensive!) sig gen is desirable, there are many occasions when a simple, non-calibrated, highly portable signal source will suffice for a quick test such as signal tracing. To that end I've designed this circuit which selectively generates square, triangle and pseudo-sine waves in three frequency ranges covering 15Hz to 2MHz.
The core of the generator is a Schmitt-trigger oscillator U1 whose frequency is determined by the setting of a 100k pot Rt and one of three switch-selectable capacitors Ct1-Ct3. These passive components should have short connecting wires to minimise spurious signal pick-up. Unused Schmitt gate inputs in the CD4093 or CD40106 IC should be grounded.
The U1 gate output is a square wave, and the voltage on the Ct capacitor is a triangular wave. The triangular wave is shaped by diodes D1, D2 into a reasonable approximation of a sine wave. Any one of these waves is switch-selectable.
The selected wave may be used as is, to feed a high-impedance load, but here it is passed to an optional buffer amplifier with a gain of 3. The amplifier comprises an LT1007 op-amp. Other op-amps would be suitable provided they have an adequate gain-bandwidth product. Capacitors C3 and C4 aid amplifier stability. C4 should be wired close to the op-amp supply pins. Resistors R2 and R3 provide a synthesised ground reference (half the supply voltage) for the op-amp. R4 and R5 set the op-amp gain. The op-amp output is AC-coupled to a 10k pot for output-level control.
The op-amp frequency response is practically flat up to ~ 20kHz and then tails off, but the output directly from U1 stays flattish up to ~ 200kHz. There is still a very usable output up to 2MHz.
The sig gen can be run from a PP3 battery and housed in a small box. Current consumption is about 8mA.

Footnote: Feedback welcome on circuit performance and suggested improvements.
First release
Last update
4.00 star(s) 1 ratings

More resources from alec_t

Latest threads

EE World Online Articles