Re: Is there a dual NE567?


ferdimh@xxxxxx wrote:

On 21 Mrz., 14:31, MooseFET <kensm...@xxxxxxxxx> wrote:
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.
This could be a solution kicking a bunch of electronics out of the
device. But it requires some modifications. See below...
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.
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.

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.
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)
http://img253.imageshack.us/my.php?image=intercom1tb0.png

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


http://www.national.com/mpf/LM/LMC567.html 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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