# Voice activated on shot switch



## leroys1000 (Aug 16, 2007)

Anyone know where I can find a voice activated one shot switch?
Can't seem to find one.
The ones I am finding are power on,not one shot.
I am trying to set up a voice controlled media center computer and
would like to be able to power it on and off by voice.
I want to tie the switch into the pins on the motherboard header,
so it has to be a one shot switch or the computer would just keep
turning on and off.
I could use something like a clapper and set power on after power fail,
but then I would end up with a dead cmos battery,so I would like to
go with a one shot on the header.

Thanks,
LeRoy


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## Frank4d (Sep 10, 2006)

How are your circuit design or modification skills? There are kits available online for "the clapper" circuit. You would need to modify it so there are two one-shots, but no latched or flip-flop output.

While it would be easy to design a circuit that simply fires off a one-shot upon hearing a single sound, it would probably be susceptable to false triggering. A circuit that only gives an output if two sounds are detected over a short time span would be better.

Upon hearing one clap the microphone would start a long one-shot (maybe 5 seconds). If a second clap is heard within the 5 seconds that one-shot output is on, it would start a second shorter one-shot (one second). The output of that one shot would be connected to something capable of driving the motherboard input (an open-collector NPN transistor should do).


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## Koot (Nov 25, 2007)

Sounds like you are looking for a *VOX circuit*, but I don't know how involved you want to get.


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## leroys1000 (Aug 16, 2007)

My soldering skills are decent and have had electronics training
through to transisters and special devices unijunction transistors
and mosfets,nothing digital.
I could,build one of those kits,but every one I am finding is for
switch on,so it is on constantly.
Something with a preprogrammed,basic control set like on off would be cool.
I wonder if it might be possble to connect an SCR to the switch circuit
on one of the kits so when the circuit turns on,the SCR would turn it back off.
I have look at vox switches,but they seem to be on too.
Wonder if there are any with adjustable delays and sensitivity.
Might have to try to design and patent a switch for this purpose.
People would probably buy it.LOL 

I have media center communicator 3 kind of running on windows 7 even
though it's made for vista.
If I can find the windows executables for shutdown/standby I can set
custom commands for those,but still need to turn the unit on.
It's amazing how much work I'll do to be lazy,Ha Ha.
But it's a cool project to work on.


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## leroys1000 (Aug 16, 2007)

Looks like the tape recorder vox circuit I have been seeing
online is probably the best bet.
It takes 6 volt operating power that should be able to run
from the 5 volt standby power on the computer power supply.
Adjust the sensitivity level so it only responds to higher level
sounds and it should do the trick.
Something like this...........
http://www.electronickits.com/kit/complete/surv/ck213.htm
It kicks on,runs the delay timer,then shuts off.
Set it for a one second delay and it should work.


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## Who's Me (Aug 29, 2006)

I was looking at the picture for that kit and noticed just above the remote out cable is a switch for remote polarity. I think that circuit may be putting out a voltage to turn on the tape recorder. If I understand what you are trying to do you want something that just connects two wires together and NOT apply voltage to the motherboard. I found this link:
http://www.electroniccity.com/shopping/pricelist.asp?prid=520
which looks like the same board and says you may add a relay for switching loads. The kit looks like exactly what you need but I would build it and check the output, if it is battery voltage then get a 5V mini reed relay (http://www.radioshack.com/product/index.jsp?productId=2062478) and a diode (http://www.radioshack.com/product/index.jsp?productId=2036268) to protect the circuit from the relay, and connect the motherboard pins to the switched contacts of the relay. Most any relay/Diode would probably be sufficient I am just giving some quick examples.

Anyone please step in and correct me if I am wrong.

Edit: I realized it may look like I am recommending buying the board in the link, I was not. I was trying to find more information on the board you were looking at and I think that one is the same thing. (only cost more and mentions the relay.)


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## leroys1000 (Aug 16, 2007)

The output on the switch line on the one I showed is
just continuity,like an on switch.
There are manual recorder switches like that,that are just a switch
and a cable that plug into the recorder.
There shouldn't be any voltage at the switch posts.
The problem with the ones I have seen that drive a relay is
they all need a 12 volt power source.
There is no 12 volt at the computer power supply in off or standby.


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## Who's Me (Aug 29, 2006)

My concern is with the polarity switch just above where the 1/8" plug is connected to the board. if it is just continuity there would be no need for a switch to reverse it.


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## leroys1000 (Aug 16, 2007)

Yeah,that's strange.
Didn't see that.
I know the remote tape recorder switches work by interupting
the power to the tape drive and every thing else is powered
by pressing the record and play buttons.
Wonder what that is for.
If it put out 5-6 volts,I could probably still use that
at the header to start the computer.

Guess I'll have to waste some money to try it later.
Right now I am still trying to figure out how to access
third party plugins in media center by voice.


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## cwwozniak (Nov 29, 2005)

leroys1000 said:


> Yeah,that's strange.
> Didn't see that.
> I know the remote tape recorder switches work by interupting
> the power to the tape drive


I did not see anything that looks like a relay on the board. I did see what looks like transistor just to the left of where the control cable attaches to the board. I suspect that the circuit uses the transistor as a switch to control a DC motor in the recorder. The transistor can only conduct in one direction and the switch allows support for recorders that can place either + or - voltage on the tip of the plug.

That switching transistor can probably be used to momentarily pull the PSU's power control line to ground to trigger the power up cycle.


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## leroys1000 (Aug 16, 2007)

Yeah,should be all it needs.
Just need to get that start pulse.
It has a sensetivity adjustment,so I should be able
to set it out of range of most sounds.
I live across from BSU in Boise,so their cannons
could probably set it off,LOL.
They also have the fireworks in the park close to here.
Have to watch that.


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## Frank4d (Sep 10, 2006)

I found a schematic for it so we can stop guessing how it works: http://www.paia.com/KRUKits/K13/K13.pdf

If you power the circuit from 5VSB of your computer power supply, the SW1 switch position needs to be set so the collector of T3 drives the power switch input to your motherboard. R9 needs to be made smaller to give you the desired one second delay.

I see a potential problem since you said in the original post that you want to turn the computer on and off. In Windows 7 the default behavior when you press the power button for one second, is to warn you to close open applications. So you would need to over-ride that so it just turns off.


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## leroys1000 (Aug 16, 2007)

Nice job finding a schematic.

Looks like providing a forward bias across the base and collector
produces a momentary pulse to trip the switch,which cause the
collector base juction to become forward biased.
Looks like it is an NPN transistor.
Gonna have the check and see if the standby power is positive
or negative.
That could be a project stopper there.
Will have to make sure it is connected with the proper polarity.
That may be what the polarity switch is for.
It looks like the trigger switch IC provides forward bias and start and stop pulses
via pin 3-4 and 5-6.
It's supposed to be adjustable,but I only see what looks like one micro sliding pot.
That might just be a switch too.
May have to get a couple of small pots to put inline.
Anyway,When the shutdown on the computer is triggered,it runs the windows
shutdown routine,which is what I want.
I don't have any apps that are hanging,so shutdown shouldn't be interupted.
I have it set to standby,so I don't have to wait for everything to load as long.
I don't want it to just shutdow because that would lose all cached data
and probably corrupt the hard drive.
The T3 transistor shound be able to pass the small amount of current
needed to trigger the motherboad,no problem.

Probably not thinking quite right,been a while.
Looks like output of pin 4 provides forward bias and pin 5
will pull down the base voltage to turn off T3.


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## cwwozniak (Nov 29, 2005)

leroys1000 said:


> Looks like providing a forward bias across the base and collector
> produces a momentary pulse to trip the switch,which cause the
> collector base juction to become forward biased.
> Looks like it is an NPN transistor.


Yes, transistor T3 is an NPN part. Don't you mean a forward bias is applied to the Base-Emitter junction, not Base-Collector? As long as positive bias is applied, it will not produce any kind of pulse and the transistor will remain conducting.



leroys1000 said:


> Gonna have the check and see if the standby power is positive
> or negative.
> That could be a project stopper there.


The ATX power supply design guide calls for a positive 5 VDC ±5% standby output with a maximum continuous allowed current draw of 2 amps.



leroys1000 said:


> It's supposed to be adjustable,but I only see what looks like one micro sliding pot.


The 5K ohm adjustment potentiometer is labeled P1 in the schematic and is the black single turn trimpot on the PCB.



leroys1000 said:


> Looks like output of pin 4 provides forward bias and pin 5
> will pull down the base voltage to turn off T3.


Turning T3 on and off is only controlled by the high or low logic level output at pin #4. The pin #5 input of the inverter doesn't pull down anything.

FWiW, the PDF file with the schematic diagram includes a pretty good description of the circuit operation. Any sound level above a set threshold will keep T3 conducting as long as the level then stays above a slightly lower threshold. Once the sound level falls below the lower threshold, T3 will remain conducting for about 10 seconds. You can change component values to shorten this period but it will not have any affect on T3 remaining turned on while the sound level is above the threshold.

You might be better off with trying to adapt a "Clapper" type circuit like this one (page has link to PDF with schematic diagram and theory of operation). It requires two distinct and closely spaced loud sounds to trigger on or off.


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## leroys1000 (Aug 16, 2007)

Yeah,meant base emmitter bias.
The pot onboard is for audio sensitivety.
Was thinking about a pot for timer delay.

I saw the one in that link too,as well as others.
The one takes a 9 volt power source and the others
needed 12 volts.
Kinda of puts them out of the range of the standby power.
5 volt positive standby is going to reverse bias the base collector junction.
That's not going to work.
So definately going to have to find one tha drives a relay.

Thank you for all the info.


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