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From: Spehro Pefhany
Subject: Re: Linear voltage change over a 30 minute period?
X-Newsreader: Forte Agent 1.92/32.572
Date: Fri, 13 Dec 2002 19:54:59 GMT
NNTP-Posting-Date: Fri, 13 Dec 2002 14:54:59 EST
On 13 Dec 2002 11:26:33 -0800, the renowned email@example.com
>I have a basic electronics question (or I would think it's basic). I
>want to build a simple DC circuit that will supply a linearly
>increasing voltage from V=0 at t=0 to V=10 volts at t=30 minutes. The
>circuit would be powered by either a battery or an AC/DC adapter.
>If linear is too complex I would be okay with just getting the voltage
>to ramp up over a time period of about 30 minutes. Can anybody
30 minutes is a fairly long time for an analog circuit. You'd
either be dealing with very low currents and a film capacitor or
more reasonable currents and a potentially leaky and otherwise
troublesome special electrolytic cap. Resetting it accurately
could also be a problem (I've used reed relays in some cases).
I suggest you consider using an oscillator (a 555 will do), a
CD4040B 12 bit counter and a R-2R ladder to generate it digitally.
If you use up one output to halt the 555 at the end of the ramp,
you'll have 0.05% resolution (steps every 0.88 second), which
leads to quite reasonable timing components for the 555.
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