Mike said:
Hi,
Does anyone have a schematic, kit, or a complete product to sense a line
level audio signal and turn a remote power amplifier on? I have done all the
searches I can think of and have not found anything. These things can't be
that rare!!
Thanks...Mike DeAngelis
The audio line activated switch is not VOX as some have claimed- VOX is
largely a radio term and describes detecting a few tens of mV or less of
microphone output. Your circuit is working off of 100mV,RMS minimum, and
up to 2V,RMS, into 10K loading. All you need to do is gain that up,
rectify, smooth, and drive a relay. Actually, you don't need to do any
of that using a single transistor and a CMOS 555. The circuit below uses
a 2N3904 to gain up the line input to a 5Vpp swing at the 555 TRIG
input. As long as the 555 receives triggers before the 15u can
discharge, which takes about 2 mins, it will remain on keeping the relay
activated. No adjustment should be necessary.
View in a fixed-width font such as Courier.
..
..
..
.. NEUT ------------->
.. GND -+----------->
.. |
.. .-----------'
.. |
.. (-)---------+ HOT -----o---v
.. 5V | o--->
.. (+)---------|---------.
.. |100u + | |
.. +--||-----+
.. \ | | |
.. \|--+--||-----+
.. \| 0.1U | |
.. | --------
.. .-----+----+------+---------+---|/ / / / |-.
.. AUDIO | | | | | -------- |
.. LINE 0.022u | | +| | +------|<|-----+
.. IN>--+-||--. | | === [120K] | 1N4001 |
.. | | [100K] [10M] 15U | | |
.. | | | | | | TLC555------. |
.. | [10K] | | | | | VCC/RST | 2N4401 |
.. | | | | | | | | |/
.. | +-[4.7M]-+-|<|-+----+----------|THRESH OUT|-[1K]-|
.. | | |1N4148 | | | | |>
.. | | 22p | | | | | |
.. | +---||---+-----------------|---|TRIG DIS|--. |
.. | | | | | | | | |
.. | | | | | | | | |
.. | | |/ | +---|CONT | | |
.. | '------|2N3904 | | | | | |
.. | |> | | | GND | | |
.. | | | | '-----------' | |
.. [1M] | | | | | |
.. | | | [100K] | | |
.. | | | | | | |
.. | | | | | | |
.. | | | | | | |
.. '--------------+-----------------+-----------+------|-----'
.. | | |
.. --- | |
.. /// '-------------------------'
..