Need help with project...

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twistedi
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Need help with project...

Post by twistedi » Thu Nov 04, 2004 10:45 pm

I have 2 audio inbputs (A)Primary and (B)Secondary.<p>(A) needs to always be active. When a button is pressed, (B) will turn on along with (A). When audio is detected in (A), (B) will turn off until the button is pressed again.<p>Although I say (A) is always active, there isn't always audio, but it is importent for (B) to be shut off as soon as audio is detected on (A).<p>I have no idea where to start with this project. Currently I am getting away with just using a switch so that I may tuen off (B) when I hear anything in (A), but (B) sometimes downs out the signal in (A).<p>Any help would be great!<p>~Chris

redrocker
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Re: Need help with project...

Post by redrocker » Fri Nov 05, 2004 9:45 am

Please clarify. It is clear that if (A) is not on and (B) button is pressed, then (B) takes control of the channel. However, it is not clear what is to happen when the (B) button is pressed and (A) is currently on. Do you want:
1) (B) to mix with (A)
2) (B) to cut off (A) and take exclusive control of the channel
3) do nothing (leave A in control of the channel)?

Enzo
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Re: Need help with project...

Post by Enzo » Fri Nov 05, 2004 3:35 pm

Is this something like the stereo will be on until someone plays the jukebox? or maybe music is on until someone keys the paging mic to make an announcement? If you gave us a specific application it might help us make answers.

twistedi
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Re: Need help with project...

Post by twistedi » Fri Nov 05, 2004 7:20 pm

Audio (A) always stays on, so when the button is pressed, (A) and (B) are mixed. Audio (A) is to never be turned off.<p>Once there is audio detected in (A) (Begins with a short tone) Audio (B) needs to stop (mute) and can not be mixed with audio (A). The reason that (A) is always on is because it is importent that the short tone be heard.<p>These both come as standard mono - 2 wire inputs, and one mono - 2 wire output.<p>Can always catch me on MSN [email protected] if you wanted to chat about this project.<p>Thanks!
~Chris

redrocker
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Re: Need help with project...

Post by redrocker » Sat Nov 06, 2004 4:50 am

I think what makes your project tough is that it is not simply a combinational logic problem but a sequential logic problem because it matters in which order events occur. Essentially you have a state problem. For example, (A) cuts off (B) if and only if (B) is on first and (A) comes on second. However, if (A) is on first and (B) comes on second, then the two are to mix. Therefore the outcome depends on the order of events.<p>Scenario 1:
S1: A audio off - initial state
B audio off - initial state
S2: B audio on - B audio on output
S3: A audio on - B cutoff, A on output
S4: B released - no change
S5: A audio off - no audio output (back to S1)<p>Scenario 2:
S1: A audio off - initial state
B audio off - initial state
S2: A audio on - A audio on output
S3: B audio on - A + B on output
S4: A audio off - B audio on output
S5: A audio on - B cutoff, A on output<p>If this is correct, your next step is to draw a state diagram. Once you do that, others can help you with the physical implementation of your hardware (discrete latches and gates or a microcontroller).

dyarker
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Re: Need help with project...

Post by dyarker » Sat Nov 06, 2004 8:51 pm

Sounds like a Public Address system. "B" is music or low priority announcements. "A" is high priority announcements.<p>The ones I've worked on used either a push-to-talk microphone, or a line from an internal telephone system. Pushing the button on the mic (or dialing the PA number) mutes "B", un-mutes "A" and triggers the tone generator. When the user hears the end of the tone, he/she speaks. When push-to-talk is released (or telephone hung-up), "A" is muted and "B" is un-muted.<p>VOX (Voice Operated transmit) is possible, but usually less desirable. If you have a second PA system using another system's output for it's "A" input, then VOX is the only way for the second system to mute it's "B".<p>Am I close to what you're doing?<p>A fast attack/slow release VOX will only lose the first few milliseconds of a tone that lasts a few seconds.<p>An always open mic paralleled with a tone generator on "A" is a bad idea. Adds noise to output, and results in embarrasing "announcements".<p>C U L -
Dale Y

redrocker
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Re: Need help with project...

Post by redrocker » Sun Nov 07, 2004 3:10 am

Yes, I agree, it does sound like a public address system. The question is whether twistedi wants the classic setup you describe or whether he wants a specific customization of one. It seems to me the question of what he wants is predicated on his definition of the word "mix". Does 'mix' mean that two inputs mutually exclusively share a common output channel (multiplex) or does it mean that two active audio sources are to be present on the output simultaneously. I have taken his meaning of 'mix' to be the latter (both sources simultaneously present on the output), which is a slightly different situation than that of a classic PA system. He'll have to clarify this distinction for the forum.

twistedi
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Re: Need help with project...

Post by twistedi » Sun Nov 07, 2004 10:35 am

ok.. <p>audio A is a phone system. It's my headset.<p>audio B is my discman<p>When I am on the phone.. and a call comes in.. my phone automaticly answers the call and warns me with a tone. When I choose.. I want to press a button during non-peak hours so that I may listen to music. So this is how it will work.<p>Normal operation = Audio A is on. Regardless if ther eis audio or not.<p>Press the button = Audio B is mixed in with Audio A *UNTIL* There is audio detected in audio A (even though I say it' mixed in with.. it's not actually there) Then it needs to stop playing audio B<p>The reason it has to be mixed is because that warning tone IS NEEDED.<p>That's it. The music does not come back on until I press the button again.<p>Basicly when ever there is audio in (A), it shuts off audio (B) and audio (B) never comes on until I press the button.<p>Hope I didn't leave anything out.<p>thanks for all the help, and sorry I have not been very clear.<p>~Chris

redrocker
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Re: Need help with project...

Post by redrocker » Mon Nov 08, 2004 1:07 am

Good. Now we have a clear idea of what you want to do. This is a cool project and should be very doable. Check the block diagram and let us know if this accurately describes what you want. If it is correct, then we can move on to thinking about the definition of each block. We can also start thinking about the installation: what wires need to be cut and connectorized; where you put the circuit board; how to power this gadget. But let's start with the block diagram:<p>Image

twistedi
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Re: Need help with project...

Post by twistedi » Mon Nov 08, 2004 9:00 pm

as far as i can tell... that looks about right :)

redrocker
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Re: Need help with project...

Post by redrocker » Tue Nov 09, 2004 5:00 am

My sense of things is that since you have been so good about participating in this discussion, twistedi, that you are genuinely interested in this project and that you don't simply want others to do your work for you. There is no pride in that anyway, and what you want is simply some guidance. As such, I am going to throw out a couple of ideas for the block definitions and let you do some research on your own to see if these ideas might be suitable. For the analog mux block, I was thinking about the CD4053, and for the Logic block I was thinking about the MC14044 (aka CD4044) Set-Reset (R-S) latch. Datasheets are available at Fairchild's website. I don't have any ideas about the tone detector block. Perhaps you would like to contribute an idea, or let other forum members offer their own.

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jollyrgr
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Re: Need help with project...

Post by jollyrgr » Wed Nov 17, 2004 2:51 pm

I have a suggestion. Instead of a tone detector how about a VOX? <p>Replace the TONE decoder with a VOX. If you are not familiar with the term, VOX stands for Voice Activated Switch. (Why the X? My only guess is that a VOX is "normally" used to operate a transmitter which is sometimes abrieviated as Xmitter.) <p>Feed the AUDIO B through one set of NORMALLY CLOSED contacts on a DPDT relay. Use the other contact "NORMALLY OPEN" setting to latch the relay; i.e. to keep the relay ON after the VOX triggers it. Put a NORMALLY CLOSED push button in the LATCH path to reset the system so you can hear B again.<p>You can build a VOX kit from parts fairly easy. Schematics are all over the Internet of various designs. Or you can build one from a kit. Here is the manual from one such kit:<p>http://www.ramseyelectronics.com/downlo ... ls/VS1.pdf<p>Take a look at page 9 of the PDF file from the above link. The diagram there shows you how to create a latching relay as I described above. When sound enters the VOX circuit it triggers the relay. But because of the momentary switch and the contacts on the relay, the relay powers itself and latches. F on the circuit board is GROUND and E is the DC out that powers the relay. But one input pin of the normally closed switch is connected to +9 volts. This allows current to flow through the switch, then the wiper on one of the sets of contacts (the left set in the picture). When the relay is triggered current then flows through the NORMALLY OPEN contact and back to the coil of the relay. Until the button is pushed the relay will stay on. This satisfies the need of "When audio is detected in (A), (B) will turn off until the button is pressed again."<p>For your audio path you will want to connect the speaker/headphone the wiper and feed the B audio to the NORMALLY CLOSED or far right contact. <p>Word of warning: You will also need some sort of isolation or padding to prevent audio from B sneaking back and triggering the VOX. And normally you don't want to simply tie two audio sources together to one speaker. So what are you to do? Use an OP amp in each audio path (set for UNITY GAIN???) and a SUM amplifier. Beaker has a great idea going but missed one of your points; to always hear signal A. Beaker's schematic would eliminate the "sneak" of audio from B back to A by use of the top switch on his/her block diagram.<p>If you can get away with not hearing A until there is a signal, then you CAN use Beaker's idea. It is the same general idea as my VOX suggestion. And it eliminates the need for isolating audio A and B. Instead of using two relays you use the one I suggested and connect audio A to the NORMALLY OPEN contact and audio B to the NORMALLY CLOSED contact. As soon as there is audio in A the relay switches over from B, latches the relay and connects audio A to the headphones.
No trees were harmed in the creation of this message. But billions of electrons, photons, and electromagnetic waves were terribly inconvenienced!

dyarker
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Re: Need help with project...

Post by dyarker » Thu Nov 18, 2004 2:49 am

Jolly, "(Why the X? My only guess is that a VOX is "normally" used to operate a transmitter which is sometimes abrieviated as Xmitter.)" Exactly. Or, Voice Operated Transmit. Typically used by hams and MARS operators in the phone patch to HF radio.<p>Since "A" is a phone in this case, the detector (tone or VOX) should latch to "A" when tone starts. Then a button press to go back to "B".
Dale Y

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