RE: TI-H: speaker


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RE: TI-H: speaker



I think I figured out what's wrong.  The red/white wires are normally at 5
volts, right? Well, to make a tick (or a short sound), the red/white wires
have to be turned NEGATIVE! This means that when the + side of the speaker
is on ground, and the red/white wires are on -, the ONLY way to make sound
is to make the red/white wires more negative than ground, thus current
flows from ground to red/white. This is why I think it is IMPOSSIBLE (well
it is still possible...but not the way they tried to do it before) to make
a transistor amplifying speaker, unless you can make the battery switch
around every time you want a tick!

>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


__
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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