Alt-BEAM Archive
Message #00190
To: Jean auBois aubois@trail.com, beam beam@corp.sgi.com
From: "Ben Hitchcock" beh01@uow.edu.au
Date: Fri, 05 Feb 1999 21:58:16 +0000
Subject: [alt-beam] Re: The BEAM clock challenge
Great idea!
I see just one problem, though: accuracy.
I'll tell you a story.
A couple of years ago I was in my final year of high school, and being the
sort of person that I am, I decided that the school assemblies were pretty
boring. For our last one, I thought that I would liven it up a little bit.
I knew a little bit about electronics, and so I decided that I would make a
time bomb. Not anything dangerous, of course (I wanted to get into uni!)
but something that would cause a bit of a stir.
One of my friends had a smoke alarm in his room that he didn't want
anymore... Instant siren. I don't know how many decibels this thing put
out, but it was pretty loud! Okay. So now for the timing circuit.
I used a straight 555 timer IC, with a 6 minute delay period. I calculated
out all the correct values, and tested it out. Ten minutes after resetting
it, the chip fired. Okay, I thought, ten minutes isn't that bad.
I then tested it again, and it didn't fire at all. I checked the voltage on
the 9V battery, and it was pretty low.
Next I got another battery and tried that. 5 minutes. OKay I thought, this
will be great.
I wired the circuit up so that the 555 timer tripped a relay that supplied
power to the smoke alarm. I set it up so that the whole unit was inside a
cardboard box, with two wires coming out to a momentary switch - my set
button. Press this, and the timer resets.
The day arrived, and I connected the battery, cut a small hole in the box to
let the sound out, and taped up the whole affair thickly in duct tape. A
couple of minutes before the assembly started to fill, I put the box
underneath a chair, pressed the reset button, cut off the wires with a pair
of scissors, and sat on the other side of the room.
TWO minutes later, it went off. I don't know if it was the temperature, if
the 9V battery suddenly got a higher charge, or what the heck the problem
was. The assembly hadn't started yet, people were still coming in, and the
effect wasn't nearly as amusing as I might have hoped.
The moral? Straight R-C timing circuits with a time period of over 1 minute
are pretty unreliable.
Your clock would be pretty cool, though. I guess if you had some way of
resetting it each day (say from a normal clock that had its alarm set for
midnight) then it would work really well.
I'd love to see it when it's finished!
Ben
----------
>From: Jean auBois
>To: beam@corp.sgi.com
>Subject: The BEAM clock challenge
>Date: Fri, Feb 5, 1999, 7:01
>
>I was wondering if you could design a BEAM clock. The sort of clock I'm
>thinking of has two output variations. The first would have 6 LEDs to
>indicate about how many minutes past the hour it is, each LED corresponding
>to 10 minutes. It would also have 24 LEDs that indicate each hour of the
>day.
>
>The second variation would use the relative brightness of some electrically
>powered light sources to indicate the time very roughly. In the first 10
>minutes of the first hour of the day, the two light sources would be either
>extinguished or off; near the end of that same first hour the hour light
>source would still be about as dim (or still off) as it was earlier but the
>minute light source would be its brightest; at the end of the day both
>light sources would be their brightest.
>
>The insides would have to be straight Nv/Nu/Suspended technology, without
>the use of conventional registers (although someone has been using latches
>to make bicores) or counters.
>
>I figure that making the minute loop (if you did implement it with a loop)
>would be trivial to make -- it could use a hexcore that has a ten minute
>delay for each neuron. On the other hand the hour loop might need both
>reliable 1-hour delays and some sort of synchronization with the minute
>loop.
>
>Can it be done? How?
>
>
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