Subject: Re: 0-100s timer using 555 IC and panel LED
Organization: The Armory
X-Newsreader: trn 4.0-test69 (20 September 1998)
From: firstname.lastname@example.org (Richard Steven Walz)
Date: 13 Sep 2002 19:42:15 GMT
In article <3D81D04D.CEE9A61A@nospam.com>,
Fred Bloggs wrote:
>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!
>This is too cumbersome and inflexible for implementation with discrete
No, it's not, it's dead simple, FOR SOMEONE WHO KNOWS HOW, instead of ONLY
knowing how to use GottVerdammt PICs.
>Your time is much better invested in configuring any number of
>PIC or microprocessor development kits for the job. You will still need
>to design the semi-analog beam break detectors and a logic-OR into the
>board. Take a look at any issue of Circuit Cellar for ideas- and pick
>one with a high-level language compiler- preferably BASIC for the
>ultimate in simplicity. The literature is rife with projects that can be
>modified to fit your application. If you insist on a razzle-dazzle
>4-digit LED display at each beam position, then drive these with the
A PC parallel port would be dandy, but the soldering and the programming
for the PIC, Parallel Port, and Soldering Discrete TTL respectively, are
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