555 timer audio switcher question

M

milo

Guest
hi everybody

i am trying to build a circuit that will switch an audio signal on and
off, using a 555 oscillator. Basically i want the audio signal to be
fully on when the oscillator waveform is hi, and fully off when the
waveform is low.
What is the best way to do this?
i have tried connecting a transistor to the output of the circuit, so
that the base termainal is connected to the pin3 output, and collector
and emmiter are connected to the audio signal path. i used a 2n3055
transistor. It worked quite well, but the problem was, even when
waveform is low, a small part of the audio signal slipped though and
could be heard. I want it to be fully off, then fully on. How can i do
this? what transistors are most appropriate? should i use two
transistors, with one switching on the other?

Thank you
Milo
 
On Sun, 15 Feb 2004 14:38:17 -0800, milo wrote:

hi everybody

i am trying to build a circuit that will switch an audio signal on and
off, using a 555 oscillator. Basically i want the audio signal to be
fully on when the oscillator waveform is hi, and fully off when the
waveform is low.
What is the best way to do this?
i have tried connecting a transistor to the output of the circuit, so
that the base termainal is connected to the pin3 output, and collector
and emmiter are connected to the audio signal path. i used a 2n3055
transistor. It worked quite well, but the problem was, even when
waveform is low, a small part of the audio signal slipped though and
could be heard. I want it to be fully off, then fully on. How can i do
this? what transistors are most appropriate? should i use two
transistors, with one switching on the other?
Click to expand...
Forget the transistors, make it easy for yourself and use a 4066
analogue-switch. One IC does all the switching you require, will work
straight from the 555 oscillator.
http://www.philipslogic.com/products/switches/4066/

--
Michael Turner
Email (ROT13)
zvxr.gheare1963@ivetva.arg
 
On 15 Feb 2004 14:38:17 -0800, delta_316@yahoo.co.uk (milo) wrote:

hi everybody

i am trying to build a circuit that will switch an audio signal on and
off, using a 555 oscillator. Basically i want the audio signal to be
fully on when the oscillator waveform is hi, and fully off when the
waveform is low.
What is the best way to do this?
i have tried connecting a transistor to the output of the circuit, so
that the base termainal is connected to the pin3 output, and collector
and emmiter are connected to the audio signal path. i used a 2n3055
transistor. It worked quite well, but the problem was, even when
waveform is low, a small part of the audio signal slipped though and
could be heard. I want it to be fully off, then fully on. How can i do
this? what transistors are most appropriate? should i use two
transistors, with one switching on the other?
Click to expand...
---
Are you trying to switch an audio signal going to speakers, or to the
input of an amp, or??? That is, what voltages and currents are we
talking about?

Is the audio signal real AC, like something that goes above and below
zero volts, or something else?

Inqiring minds want to know!-)

--
John Fields
 
On 15 Feb 2004 14:38:17 -0800, delta_316@yahoo.co.uk (milo)
wrote:

hi everybody

i am trying to build a circuit that will switch an audio signal on and
off, using a 555 oscillator. Basically i want the audio signal to be
fully on when the oscillator waveform is hi, and fully off when the
waveform is low.
What is the best way to do this?
i have tried connecting a transistor to the output of the circuit, so
that the base termainal is connected to the pin3 output, and collector
and emmiter are connected to the audio signal path. i used a 2n3055
transistor. It worked quite well, but the problem was, even when
waveform is low, a small part of the audio signal slipped though and
could be heard. I want it to be fully off, then fully on. How can i do
this? what transistors are most appropriate? should i use two
transistors, with one switching on the other?

Thank you
Milo
Click to expand...
I use a simple tranisitor to switch the audio along with the
video on my webcam page below. It is a line level signal. To
prevent bleed over on full off, you may need to connect the audio
feed to a ground when it is in the off position.

http://www.geocities.com/zoomkat/ppswitcher-demo.htm
 
if you can find some 4066 or equ bilateral mos gate switch
you can turn off the audio very nicely..
P.s. you will have to do this at the preamp stages because
this unit is very low current drain compared to what your
currently using :))


milo wrote:

hi everybody

i am trying to build a circuit that will switch an audio signal on and
off, using a 555 oscillator. Basically i want the audio signal to be
fully on when the oscillator waveform is hi, and fully off when the
waveform is low.
What is the best way to do this?
i have tried connecting a transistor to the output of the circuit, so
that the base termainal is connected to the pin3 output, and collector
and emmiter are connected to the audio signal path. i used a 2n3055
transistor. It worked quite well, but the problem was, even when
waveform is low, a small part of the audio signal slipped though and
could be heard. I want it to be fully off, then fully on. How can i do
this? what transistors are most appropriate? should i use two
transistors, with one switching on the other?

Thank you
Milo
Click to expand...
 
thanks for replying

ideally i want my audio switcher to switch either AC line level or AC
to amplifier level. Would this cmos chip be good for this?
 
delta_316@yahoo.co.uk (milo) wrote:

thanks for replying

ideally i want my audio switcher to switch either AC line level or AC
to amplifier level. Would this cmos chip be good for this?
Click to expand...
Your spec is still rather vague. What does 'either AC line level or AC
to amplifier level' mean? Do you mean you want to switch either:
- a low voltage, low current AC input signal
or
- a high voltage, highish current amplifier output signal.

If so, then the former would be easier, so why not forget about the
latter? Switching the low-level signal probably *could * be handled
with a CMOS 4066 chip.

--
Terry Pinnell
Hobbyist, West Sussex, UK
 
Without putting numbers to 'high', 'low', 'AC line level',
and so many other expressions; then many are simply ignoring
your post. Any response would be futile. If you want a junk
science answer, then use a high pass or low pass filter. Is
this reasonable? Only if the answer does not include numbers.

milo wrote:
thanks for replying

ideally i want my audio switcher to switch either AC line level or AC
to amplifier level. Would this cmos chip be good for this?
Click to expand...
 
bloody 'ell... all these numbers..... . . . ..

ok, i think i know how to put it know. i want to use a switch,
triggered by the 555 output pulse, that is capable of switching large
waveforms.

by 'large' i mean waveforms that are up to 10v p-p amplitude. this
would be the absolute maximum though, i think that most wavforms i
would use would be under 5v p-p. maximum current probably about 10 mA
..i spose that a cmos wouldn't be able to handle this.
 
delta_316@yahoo.co.uk (milo) wrote:

bloody 'ell... all these numbers..... . . . ..

ok, i think i know how to put it know. i want to use a switch,
triggered by the 555 output pulse, that is capable of switching large
waveforms.

by 'large' i mean waveforms that are up to 10v p-p amplitude. this
would be the absolute maximum though, i think that most wavforms i
would use would be under 5v p-p. maximum current probably about 10 mA
.i spose that a cmos wouldn't be able to handle this.
Click to expand...
More numbers: the 4016 and 4066 can dissipate up to 100 mW. So,
assuming your 10 Vpp is roughly 3 V rms, that means the current
through the switch could be up to 30 mA absolute max. Therefore 10 mA
should be OK. But voltages *must* remain within the CMOS chip's supply
limit.

I suggest you now track down and read the datasheet.

--
Terry Pinnell
Hobbyist, West Sussex, UK
 
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