"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.

http://en.wikipedia.org/wiki/78xx

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(setq (chuck nil) car(chuck) )