"chuckcar" wrote in message
...
"hhgggff" wrote in
news
My friends dad is building a Tardis for his grandson.

We have rigged up the blue flashing light using a 12 volt car battery,
we now need to sort out the sounds.

I was thinking of using an old cars cassette tape, but I have an old 9
volt portable cassette handy.

Will it burn down the TARDIS if I use that instead ?

The tape motor will run at the wrong speed for one. What you need is a
voltage regulator. A 7809 should do the trick. The 7800 series convert DC
voltages. Granted a transformer does it, but these handle *much* wider
voltage inputs and are tiny in comparison. A 7812 hooked to the +12v
connection with the other connection hooked to a 200 microfarad capacitor
should give you a rock solid +9v out. You'll need a piece of breadboard
about 1" square to mount these on.


You should read up on a subject you know little about before giving advice
to others.

Even in older cassette recorders the motors had centrifugal speed governors
and modern ones have an IC speed controller (otherwise they'd run slower and
slower as the battery was used).

Your mention of transformers is misleading, without a "chopper" circuit to
convert DC into AC a transformer will burn out.

The OP is best advised to ask people who are equipped to give accurate
advice, such as the folk on News:sci.electronics.basics .