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'[EE] My First Original Circuit!'
2007\03\06@050709 by Marcel Birthelmer

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part 1 1055 bytes content-type:text/plain; charset=ISO-8859-1; format=flowed (decoded 7bit)

Hi all,
I'm sure to most of you this will be boring, but this circuit
represents the first time I've come up with a useful, non-trivial,
functional analog(ish) circuit, so I'd like to share it with the
group. Circuit is attached, or available at
http://marcel.carrietech.com/switches.png

There are three switches mapped to two outputs. SW1 = 01, SW2 = 10,
SW3=11. The idea of this circuit was to prevent SW1 and SW2 being
pressed at the same time to cause the output to look like SW3. (If SW3
is pressed along with either of the other two, the output will be 11.)

In the idle state, both voltages are low. When one switch (assume
it's SW1, without loss of generality) is closed, the transistor Q2
turns on, dropping its collector voltage (and thus Q3's base voltage)
close to 0. Q3, in turn, is cut off, leaving no current to flow
through SW2 if it is closed. The same takes place if SW2 is pressed
first. When SW3 is closed, both outputs are forced high via the
diodes.

Any comments are welcome.
Thanks,
- Marcel


part 2 14252 bytes content-type:image/png; name=lab2_switches.png (decode)


part 3 35 bytes content-type:text/plain; charset="us-ascii"
(decoded 7bit)

2007\03\06@055841 by Michael Rigby-Jones

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{Quote hidden}

I think you have just re-invented the priority encoder!  A 74LS148 would do this job, and you could even exapnd it up to 8 inputs.

Regards

Mike

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2007\03\06@060624 by John Chung

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Good attempt.  Good exercise.

John


--- Marcel Birthelmer <marcelb.listsspamKILLspamgmail.com> wrote:

{Quote hidden}

> > --

2007\03\06@060716 by Marcel Birthelmer

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Mike,
not quite. In a priority encoder, whichever input has higher priority
will always clobber the others. In this circuit, though, the button
that's pressed first has priority as long as it's pressed.
- Marcel

On 3/6/07, Michael Rigby-Jones <.....Michael.Rigby-JonesKILLspamspam.....bookham.com> wrote:
>
>
> >{Original Message removed}

2007\03\06@062756 by Rikard Bosnjakovic

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On 3/6/07, Marcel Birthelmer <EraseMEmarcelb.listsspam_OUTspamTakeThisOuTgmail.com> wrote:
[...]
>  In the idle state, both voltages are low. When one switch (assume
> it's SW1, without loss of generality) is closed, the transistor Q2
> turns on, dropping its collector voltage (and thus Q3's base voltage)
> close to 0. Q3, in turn, is cut off, leaving no current to flow
> through SW2 if it is closed. The same takes place if SW2 is pressed
> first. When SW3 is closed, both outputs are forced high via the
> diodes.

Brilliant.

Given the explaination, I didn't have too much difficulties
understanding the circuit, but I would have most likely never been
able to design something similiar myself.

How do you professionals do when you design stuff like this?


--
- Rikard.

2007\03\06@063054 by Michael Rigby-Jones

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>-----Original Message-----
>From: piclist-bouncesspamspam_OUTmit.edu [@spam@piclist-bouncesKILLspamspammit.edu]
>On Behalf Of Marcel Birthelmer
>Sent: 06 March 2007 11:07
>To: Microcontroller discussion list - Public.
>Subject: Re: [EE] My First Original Circuit!
>
>
>Mike,
>not quite. In a priority encoder, whichever input has higher
>priority will always clobber the others. In this circuit,
>though, the button that's pressed first has priority as long
>as it's pressed.

Ahh, I understand now.  I initialy thought you were just trying to prevent simultaneous pressing of SW1 and SW2 causing the same output as SW3.  In that case it seems like a neat circuit.

Regards

Mike

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2007\03\06@094331 by John Chung

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--- Rikard Bosnjakovic <KILLspamrikard.bosnjakovicKILLspamspamgmail.com>
wrote:

{Quote hidden}

 I am not a professional designer but my
understanding depends mainly on my knowledge and
application of previous work. You ought too build more
circuit with simpler design first and start applying
from there. In electronics, application of simple
designs from the TEXTBOOK is crucial plus some
experience on the breadboard. It is really not a
problem once you break it down. Perhaps you need to
read on circuit analysis first to be quicker in
identifying circuits. Once again try and try again.
Just match the theory in your mind to the circuit.

John





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