Australian Standard Phone Ringer

[@rt]

Hi Guys
Well inspired by Dave’s last video I decided to do the Australian phone ring duration the hard way
The duration is: 400ms ring, 200ms delay, 400ms ring, 2000ms delay, repeat.

hehe...


Both chips reset each other, so if the decade counters started batty it would fix itself.
Sometimes decade counters can start with more than one bit set, and all bits continue through the counter until reset.
This schema doesn’t include the rest of the circuit to drive the ringer solenoid, just the ring durations.
If you see any simplification please let me know
Cheers, Brek.

[Berni]

Here you go a simplification



But it is cool to look at old designs from back when there was none of this fancy newfangled microcontroller rubbish and amazing things ware being built out of piles of 74xx

[Tac Eht Xilef]

It's also cool to look at old designs from back when there was none of this fancy newfangled 74xx rubbish and amazing things were being built out of springpiles

https://youtu.be/VzIXvO6RahQ

(The 3 on the right are the 3 ring 'phases')

Very similar machines were used here in Oz right up until the demise of ARF/ARE gear around the turn of the century (and beyond - there were still a few of the little ARK-style motor-generator ringers installed in smaller places, left running to feed ring to special services like outdoor extensions etc., when I left the Evil Empire in the mid/late 00's. Although by that time most of even those had been replaced by solid state ring generators.)

[@rt]

I used bakelite knobs for each 555 oscillator and a real transformer if that counts for something

[@rt]

I am stuck here at how to tell the phone was picked up to stop the ringer and connect the voice circuit.
If there was a relay in series with he phone ringer circuit, and the phone went lower impedance when it was picked up,
maybe the relay would then latch with he extra current to the relay coil,
but this stops making sense to me in practice where the relay would have to be held on.
So does another current source kick in through the relay switches to hold it latched to the voice circuit?

I have the high voltage oscillator and timing worked out to ring the phone ok, but would be nice to keep going.

Cheers, Brek.

[Berni]

I am not sure of the exact numbers but phone lines have 48V on them when open cirucit. Once you pick up the headset the low resistance speaker comes in to circuit and drags the voltage down to a few volts.

I have no idea how they detected that in the old days but it would make sense that a relay coil would be used for that since a picked up phone has a DC bias running trough it that serves as its "power supply", but i suspect the coil of the relay would have to be fairly sensitive.