Is there a dual NE567?

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I\'m pretty sure there isn\'t, but what\'s your application?

Maybe there\'s a better way.

The circuit is an intercom over a 2-wire interface. The goal is to be able to use many stations on the same two wires and call them. My idea was to superimpose an ultrasonic tone on the speech signal to do that. So one NE567 is used to decode the tone and the other is used to make it (a NE567 is a nice sawtooth oscillator with only two external components). I could also use a 555 for this purpose, but combining two NE567 would save a chip and an extra 555 would never save one.

I haven't found any, but I could email the schematic to you. Maybe you find the perfect solution...?

Ferdinand

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Maybe. ;)

In keeping with the spirit of the newsgroup, though, it would be
better if you posted it somewhere where we can all access it.  Since
you can\'t access any of the binary USENET groups through Google that
rules out alt.binaries.schematics.electronic, but maybe you can post
it to a website somewhere and then post the URL here?

20 Mar 2008 14:04:38 -0700 (PDT), snipped-for-privacy@gmx.de wrote:

there's a better way.

I'm going to be the first in this thread with a "use a PIC" solution:

The PIC can read some dip-switches to know its station number. The ADC can sample the signal from the two wires and code can look for this stations frequency. The call signal can be a tone made by wiggling a port output.

Now for a non-PIC based idea:

The LTC6906 makes a squarewave output with just a single resistor. Changing the resistor value makes different frequencies for selecting which station to call. The part is about as small as the capacitor you'd need with any other sort of oscillator.

The decoding could be done by making basically a superhet radio. An oscillator can be set just a small amount off the frequency for the call signal and then a simple mixer could turn the call signal into a tone in the audio band that is sent to the speaker to alert the user.

This could be a solution kicking a bunch of electronics out of the device. But it requires some modifications. See below...

I'd prefer the sawtooth generated by the NE567, because it has a lower harmonic content. But, if I find a source of these, I'll consider them. Note that this is a hobbyist's project, so I need to buy in small quantities.

I think you misunderstood the design. The tone is intended to unmute the speaker, so that the real call can be done by voice. That's why the call tone needs to be ultrasonic.

Here is the schematic (my webserver is down at the moment, so I had to use imageshack)

Some explanations: The intercom is going to be used to link several flats spread over two houses. Because people (especially some old women) live there, the intercom needs to be as easy-to-use as possible, i.e. press button, speak, release button, await answer.

You too can't expect these people wait for the line to become inactive, so an interlock is included to avoid collisions on the line. That's why the line is raised to 2V while speaking, allowing simple detection whether the line is in use or not. Sometimes there will be need to call everyone, so every station will react on a DC level on the line above 5V and unmute the speaker. There is also support for an entry-phone. Because one can't expect strangers to understand what a PTT is for, the PTT is moved into the other stations. The TAA4761 is a quad operational amplifier with high-current open- collector output.

BTW: I'm from Germany so please be gentle with my English...

Ferdinand Meyer-Hermann

first in this thread with a "use a PIC" solution:

based idea:

Try

They carry lots of linear stuff.

Yes, perhaps I did. I had assumed that a person had to do something at the receiving station.

Here is the schematic (my webserver is down at the moment, so I had to

There is something wrong with the image. I can't see much of it. There is a big square blank in the middle.

Are they talking to a central station?

Your english is quite good.

Perhaps more later. I've got to run.

says that National has discontinued the LM567 but still makes the low power version, the LMC567. You should have no problem finding a vendor of National Semiconductor in Germany.

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No, there is no central station except a central 15-20V power supply. All stations are wired in parallel. So there needs to be sort of an algorithm to arbitrate who is will use the line next.

I have no trouble getting the LM/NE/SE 567. The problem is the LTC6906.

Ooops, I really don't know what has happened to the schematic, but here is another try:

Happy Easter! Ferdinand Meyer-Hermann