Subject: Re: 0-100s timer using 555 IC and panel LED
Date: Wed, 11 Sep 2002 00:43:14 +0200
NNTP-Posting-Date: Tue, 10 Sep 2002 22:37:21 +0000 (UTC)
X-Mailer: Mozilla 4.78 [en] (Win98; U)
555 is not a good choice, you need a crystal controlled clock generator ..
Jeff Lawlis wrote:
> I am a Physics teacher with a basic understanding of electronic
> circuits. I would like to build an elevated ramp with adjustable
> slope, whereby an object would be allowed to roll down the slope. At
> 5 places along the ramp, I would like to incorporate phototransistor -
> LED (focused) pairs, such that when the light beam is interrupted, it
> activates a relay. The main goal would be to time the object at
> different locations, in order to caluculate the velocity at each
> position. I would like to use four digit LED diplays, displaying time
> to the nearest hundredth of a second.
> My questions are as follows:
> a) I was thinking of using a 555 timer in astable mode,
> operating at a frequency of 1000 Hz. This would be coupled to
> appropriate counters and IC chips to convert to 7-segment LED display.
> What is the "real" accuracy of such a circuit in this mode?
> b) Can I use the output of one 555 timer with 4-5 counter
> circuits (one for each group of LED displays)?
> c) Once you remove the input from a counter chip, does that
> "freeze" its output? I need a way of freezing the time at each
> location, once the light beam is interrupted.
> I know this is an ambitious project for me, but the kids would love
> it, I can guarantee!