RE: TI-H: speaker

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RE: TI-H: speaker

One possibility would be to run it through a "not" (7404) gate,
this will reverse your voltages. :-)

-----Original Message-----
From:	Thayne Miller [SMTP:yomaster@geocities.com]
Sent:	Sunday, August 31, 1997 11:39 PM
To:	ti-hardware@lists.ticalc.org
Subject:	TI-H: speaker

First of all, before I go into any major detail, has ANYone gotten the
transistor-amplifying speaker to work??? I built one and it works, but it
constantly makes a high-pitched noise, even when the 85 is off.

I did some testing on a bread-board and found some very wierd things (well,
I don't know much about electronics, so if someone could straighten me out,
I would be very happy =)). First, I tested out a simple circuit with the
speaker (actually a piezo buzzer). I wired the + side of the speaker to the
red/white (clock/data) wires of the link port; the - side to signal ground
(shield). I found out that the red/white wires are constantly active (5V).
This means that the 85 uses reverse-logic (a zero means active and a 1
means inactive). This configuration constantly made a high pitched sound
(because there was a closed circuit). I then switched the red/white wires
to the - side and the ground wire to the + side. THIS WORKED! All the
programs with sound worked fine (yeah...big deal ;)) I don't understand why
the current flows through the speaker backwards.

I proceeded to add the transistor into the circuit. I wired the + side of
the speaker to the + battery terminal, the - side to the collector of the
transistor, the red/white wires to base, and signal ground to the emitter
(try and picture it). This worked, but with the high pitched sound. I
switched the + and - sides of the speaker, but now it didn't even work at
all!!! >=( I am confused, because it seems that the red/white wires can
make current go though the speaker backwards, but the battery cannot
(someone that knows some electronics help me out :)) I do know that the
red/white wires act as a "switch" that let current flow from the + battery
terminal to signal ground, thus making sound, but how do I wire it so that
it lets current flow from + to ground, when the red/white wires are
INACTIVE??? (remember that since the red/white wires are active in "normal"
mode, the "switch" would let current flow which makes sound).

To get to the point, I need help in finding a transistor that lets current
flow when base is INACTIVE (0V), or figure out why the crap current can
flow BACKWARDS through the speaker only in SOME circuits. :{

To see the actual schematic of this speaker, go to
http://www.geocities.com/SiliconValley/Lakes/5081/Richfiles.html and look
in the SPinTerface cart page.

Thank you so VERY much for your time.

__
Thayne Miller
Email: yomaster@geocities.com
Home Page: http://www.geocities.com/SiliconValley/Heights/5084

"Yes, well, that's the sort of blinkered, fitestine, pig-ignorance
  I've come to expect from you non-creative garbage!"
      -Monty Python
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