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Re: [ST] Helmet camera
- Subject: Re: [ST] Helmet camera
- From: "Mike Bostock" <mike@xxxxxxxxxxxxxx>
- Date: Fri, 25 Apr 2003 23:35:56 +0100
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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