Hello, I want to ask you how to implement notification system with multiple terminal devices,
which allows to make call from any terminal to any other terminal? Main
constraints are not using programmable chips/MCUs (only general-purpose
and specialized hard logic), using wired communication instead of
wireless, not having a separate cable between every two terminals,
having single power source instead of batteries everywhere. There is no
need to transmit voice or text - just targeted notifications in the
style “doorbell between any two rooms”. The receiver must know who sent
I would like to implement in my home a kind of notification system to
make calls between rooms, either by designing it myself or by finding
an existing design. Basic idea is that there will be several terminal
devices (below called “terminals”) A, B, C, D, ... at different places.
Each terminal will have separate button for every other terminal (so for
example terminal A will have buttons “B”, “C”, “D” and so on), separate
LED for every other terminal (thus terminal A will have LEDs “B”, “C”,
“D” and so on), and one bell (like usual electric doorbell). The buttons
will be used to make calls, and the LEDs will indicate the caller.
How it should work
Suppose Alice (who is currently near terminal A) would like to call
Bob (who is currently near terminal B). Then Alice pushes button “B” on
the terminal device A. As a result, the LED marked “A” lights up on the
terminal B, and the bell on the terminal B rings. Terminals C, D, etc.
stay quiet. Bob hears the bell and sees the LED and goes to terminal A
to look/ask what happened.
There will be at most 16 terminals and at least 5 terminals.
Instead of multiple LEDs there might be one or two seven-segment displays on every terminal, to show caller’s ID.
Optionally, there will be also button "call all other terminals at
once", e.g. to call B, C, D etc. from A simultaneously. This (as well as
other optional features) will largely depend on whether it simplifies
or complicates things.
All terminals will be powered from single power supply (instead of
having batteries in every terminal), thus at least two wires will go
through all terminals (Vcc and GND). Depending on schematics, third
power wire might be needed. Further, low-frequency wire-based
communication is preferred over high-frequency wireless communication
for several reasons, including lack of experience with radio
frequencies. Up to 8 additional wires for communication (i.e. not
counting power wires) should be acceptable, with all cables meeting at
single point (the location of power source). Alternatively, there might
be additional mediating device which is connected to every terminal.
There may be problem if two calls are made simultaneously from
different terminals. This can be mitigated by locking terminals B, C, D
once terminal A is activated, and unlocking them back once A is
deactivated. Anyway, this issue can be ignored completely, assuming that
any combination of simultaneous calls will not destroy the circuitry.
I have a (still rough, no schematic yet) idea of how to accomplish
the above project with general-purpose hard logic (gates, counters,
encoders, decoders). Each terminal might send two bursts of impulses,
one burst encoding caller, another burst encoding receiver. One or two
communication wires might be enough. This seems to be nontrivial but
viable. Perhaps I will have to find someone to review my schematics
before trying to implement it.
However, I have strong feeling that this or similar problem is
already solved and implemented in some specialized integrated circuits
or electronic modules that can be just plugged in with minimal/moderate
additions. I'm unsure how to search for such a solution, though, as well
as whether the cost will be viable for me. My attempts at
“multidirectional doorbell”, "home notification system" and several
other queries did not provide anything relevant.
Maybe remote controls might be repurposed into terminals (calling
part), with different commands for different receivers and different
protocols for different callers, but then either every receiver must be
able to understand all callers (multiple receiving modules in every
terminal?), or there must be at least 20 different commands supported by
remote control (to cover 5 terminals) to 240 different supported
commands (to cover 16 terminals). I did not investigate the idea with
remote controls closely, though.
Can you point to an existing solution with multiple "peer" terminal
devices which is primarily intended for making simple non-voice
Or to any ideas of how this might be implemented?
Or to existing places on the web where the same thing is discussed under
different name / in different setting?
Are there existing solutions to other problems (like remote controls)
which could be adapted for this purpose?
Please note that I will not accept answers suggesting programmable
chips/microcontrollers/anything which must be programmed, even if this
will really simplify remainder of circuit. (I am not saying such answers
will be totally useless, since other people with different skills may
have the same problem! Also, a few jumpers or micro-switches inside
every terminal device to assign unique IDs to terminals are acceptable,
even though this can be considered 'programming'.)
If nothing else, I will try using gates and counters. Even if the
whole thing will turn out infeasible for me at this point, I'll still be
glad to know what are existing possibilities.
Any input is welcome!