Re: TI-H: speaker
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Re: 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.
>
> 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. :{
:) ... Try this ...
(vcc)-._________________ Legend: (vcc) Input voltage
| | (gnd) Ground (+ link shielding)
| .----| (in) red + white wires
| [C] [S] [R] resistor
[R] `----| [C] capacitor
|___ | [T] transistor
| `-[P]--[T] [S] speaker
(in)--[R]--[T] | [P] variable resistor
| |
(gnd)_______|___________|
This is what I have in my TI-Sound box. It plays the music pretty
loud (I'm using 9V battery as input voltage), and doesn't consume
any power when inactive. The capacitor filters all unneded high
noise caused by 1-bit sound output of the calc, while the transistors,
working in switch mode, invert the signal and amplify it to 9 volts.
The capacitor I used is about 50 uF, while the resistors are around
1 kohm, but that heavily depends on the beta of the transisors used.
I hope this helps,
Vojtech.
References: