by W.A. Steer  PhD
About...

High stability 25kHz sinewave signal generator

Single-bubble sonoluminescence experiments require a high stability sinewave oscillator operating at around 25kHz, and tunable to within a few tens of Hertz. Although sufficiently good quality general-purpose signal generators are available commercially, they are typically well beyond the budget of school and even university undergraduate laboratories. This page presents notes on a low-cost, high stability homebuilt oscillator with limited frequency range, ideal for sonoluminescence experimentation.

Unfortunately the design and construction of the oscillator was not properly documented at the time it was built. Since I've had quite a few enquiries about the signal generator, I've brought together here most of the information I do have. This information does not constitute a full write-up, but rather acts as a guide for someone with competence in electronics.

 circuit.gif : the definitive circuit diagram for oscillator &
               buffers. DOES NOT INCLUDE power supply section.

 power.gif   : power supply for oscillator FROM MEMORY.

 parts1.gif  : ignore the circuit-diagram scrawl, the previous
               (lab-book) scan has the definitive circuit.
               The part numbers shown are RS stock numbers as
               of 1997.

 parts2.gif  : again the circuit scrawl is not definitive, but
               indicative of my thoughts regarding Veroboard
               layout.

 parts3.gif  : more ideas for parts - may be duplicated on next
               sheet.

 
 parts4.gif  : Maplin order form - mechanical parts.

All parts are available from RS components (http://rswww.com/), some 'cosmetic' parts knobs, feet etc were obtained from Maplin (http://www.maplin.co.uk/). You might be able to get the bits from Maplin - though they've reduced their range a lot recently.

It is crucially important that the 1000pF capacitor is of the Mica type (again could easily be 2 UK pounds), otherwise the thermal stability of the circuit will be severely compromised. You should also use high quality potentiometers (similar to those specified), which will probably cost 3 to 5 UK pounds a time.

The resistor *types* aren't specified, but 1% tolerance metal film resistors have good stability and won't break the bank! Use either 0.25W or 0.6W power rating.

The parts lists above are not comprehensive. Extras including power-on LED, series resistor for it, the Veroboard itself etc aren't given.

Don't ask for any other written documentation - this really is all I have, apart from the data sheets for the IC's, which you can probably download off the web these days!

Update: May 2007

A correspondent mentioned that NEC make a reasonably-priced pin-for-pin alternative, the NTE864. Its datasheet can be found at http://www.nteinc.com/specs/800to899/pdf/nte864.pdf

Someone asked why I have the TTL ouput. The answer is that TTL output is useful for synchronising oscilloscopes (it's nicer to synchronise to a square-wave!) and also has the added bonus that by using a separate output, if the scope loads it in any way, it won't affect the amplitude of the sinewave (which needs to be stable).

Use the oscillator somewhere away from any source of heat, as it still has very slight thermal drift; don't put the it on top of (or inside) a computer or power-amplifier. Build it into its own case so it doesn't react to a draft, and you won't have any problems! Be absolutely sure to use the silvered-Mica capacitor as indicated.