[Coco] Telephone System

[Brendan Donahe]

This is interesting, John Mark.  I have often thought of a demo (at a VCF,
not CoCoFEST) to include my pair of acoustic-coupled TI thermal printer
terminals and associated rotary or keypad Bell telephones, but thought I'd
need to get my hands on a PBX to do so.  This seems much simpler!  Thanks
for sharing!

If I weren't flying to the fest or wasn't already loaded with other things
to bring, I'd consider bringing something to hook up to your demo system.

Brendan

On Sun, Apr 28, 2024 at 6:43 AM John Mark Mobley via Coco <
coco at maltedmedia.com> wrote:

> All,
>
> How to make a simple analog phone system:
> https://www.youtube.com/watch?v=8bwLjU90puA
> Note 1: The resistor is unnecessary if the telephone devices are in series.
> Note 2: With a 300-ohm resistor and both phones off the hook the system
> draws about 5 mA and the audio is softer.
> Note 3: Without a resistor and both phones off hook the system draws about
> 9
> mA and the audio is louder.
> Note 4: If you hang up one or more phones then the system draws about 0.0
> mA.
> Note 5: A 100-ohm resistor might be a good idea to protect against a short
> circuit.
> Note 6: If the battery and the two phones are in parallel then put a
> resistor in series with the battery.
> Note 7: The polarity of the battery does not matter.
> Note 8: There is no dial tone, dialing, or ring, just talk.
> Note 9: You can test this at home before the show.
>
> Please consider bringing something to the show to hook up to the phone
> system.
>
> -John Mark Mobley
>
>
>
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