Author Topic: Empire Liberty Payphone  (Read 3176 times)

Offline dsk

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Empire Liberty Payphone
« on: October 27, 2013, 10:06:19 AM »
Hi
I have a feeling of great potential to learn more about payphones, in other words I have a feeling of knowing nothing.

This stainless steal box named Empire Liberty 503 is an extremely simple payphone.
The coin handling are 100% mechanical, a weight and size controlling system are designed to sort out to big, or to small coins, a magnet stops magnetic coins.  
When putting in the right coin. (now modified by me to accept NOK 10)
a micro-switch counts it on the way to the coin box.

I dont know about the circuit diagram, but it is based on the NE 554, with a push button dial.
The network looks like a standard network, and the dial p.c.b. are probaly modified, since the integrated circuits are painted so we cant identify them. A little professionally looking p.c.b. are wired up to the dial p.c.b. in a way that looks less professional.

How does it work?
Going off-hook, and the transmitter are blocked.
Dialling 0 as the first digit and the transmitter works.
Dialling 1 as the first digit and the phone has a long flash of about 1 sec.
All other dialing just works, but the transmitter are still blocked.

Adding the right coin, the transmitter unblocks when the coin hits the micro-switch at the inlet of the coin-box.

It seems like the nothing blocks the telephone except when hanging up, or disconnecting the phone, so you may talk for as long as you want.

dsk


« Last Edit: October 27, 2013, 11:13:12 AM by dsk »

Offline dsk

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Re: Empire Liberty Payphone
« Reply #1 on: October 27, 2013, 12:59:30 PM »
This made me thinking ;D  (proud!) ;D

As described in another thread, making a circuit blocking the transmitter until coin is detected should be simple, when you just know how. (That's where the thinking was needed)

I ended up with an extremely simple circuit made of what I had, actually only one basic component! ( $1!)
The thyristor has been almost a useless component in my eyes. Here it is the solution.

To test, I needed a telephone with a circuit who dont break the dial tone when I remove the transmitter, one with an extra button, to indicate collected coin, and one I could use for experimenting without risking to ruin a fortune.

Look at the pictures:




This circuit works, but it is polarity sensitive, so just reverse the ring/tip if it doesn't work.

Of-course always a unexpected problem, shouting in the transmitter, the resistance increases, and suddenly the transmitter are blocked again.  Then I had to limit that, and the first (and best?) a 680 ohms resistor as a shunt to the transmitter solved it.

Not exactly Bell laboratory's, but good enough for me, so far. 

dsk

Offline dsk

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Re: Empire Liberty Payphone
« Reply #2 on: November 03, 2013, 04:06:26 AM »
I guess I have made it Norwegian  :D

Here are a scan of the old label, and a new label in Norwegian.

dsk