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Re: [ST] Helmet camera



In your message regarding Re: [ST] Helmet camera dated Fri, 25 Apr
2003 10:15:38 -0700, Neil Lindsey said that ...

>NL- 
>NL- On Thu, 24 Apr 2003, Mike Bostock wrote
> 
> > BTW it requires a 12V regulated power supply (the bike can peak to
> > 13.5 volts) any easy way of regulating this?
>NL- 
>NL- On Thu, 24 Apr 2003, Bill Swartz wrote:

<snipped>
>NL- The voltage will drop as the load (current drain) increases.  Don't believe
>NL- me? -- check the output with a multimeter.  A properly regulated power
>NL- supply does not vary with the load current, so the open-circuit voltage
>NL- should read the same as when it is loaded down by the device it is powering.

I believe you!


>NL- 
>NL- To create a properly-regulated 12V supply, the first thing you need is an
>NL- unregulated power source that is ALWAYS higher than the target regulated
>NL- output.  Such is not the case with automotive power systems, since the
>NL- output can go down to (or, in some instances, below) the 12V nominal
>NL- reading.  There are ways to up this source voltage.  Some are more
>NL- complicated than others, but a 'voltage doubler' made with capacitors may
>NL- suffice for low current applications.  Also presuming a low current
>NL- application, you may be able to regulate this increased voltage with nothing
>NL- more than a carefully-chosen resistor and a zener diode (12V in this case).
>NL- If the current requirements are higher then you may need more circuitry that
>NL- involves a power transistor to pass the additional current required for
>NL- increased loads.

I don't think the current requirement is great.  The Zener diode
solution will probably work well and I have seen its use in another
application (Autocom powered Icom PMR radio).  I can manage to wield
a soldering iron - how do you orientate the Zener diode in respect to
its markings in the power cable?

- -- 
Mike Bostock
http://www.toothfairy.co.uk/
Wales & SW ST Riders
http://www.sprint-st.org/

'99 Red ST

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