beginner questions

[Alastair W Heptonstall]

I don't know how much info you were wanting about the power 
supply thing, but what I usually do is to use a supply with a higher 
voltage than necessary (such as 15v for a 12v circuit as you 
suggested) and to put this through a voltage regulating IC  (which 
you can find pretty easily in a maplin of farnell catalogue) to bring 
this down to 12v.  This means you always get a pretty smooth 
supply.  Watch the power consumption though because these 
things get rid of the difference between input and output voltages by 
heating up, so you may need more than one.  They're really easy 
to use as they only have three pins, these being for ground, high 
voltage in and low voltage out (the catalogues normally list which 
pin is which under a strange diagram of the case type)

As far as the +15 to -15 supply is concerned there is a pretty 
simple circuit using the relatively cheap 555 timer ICs.  I'm not sure 
if this circuit is given on the 555 data sheet, but if you want I can 
look it out for you and scan it.  Again you may need more than one 
of these circuits if you are drawing a large current.

Hope it all goes well.

Alastair Heptonstall

University of Glasgow
Department of Physics and Astronomy