Telephone On-Hook Current

So are you trying to power your circuit from the line, or just know when the line is disconnected from the phone?

Knowledge. Its use is for logic controls. ...Jim Thompson

I never saw a PAL version, but the NTSC was 4*3.57954545 MHz

I had $65,000 worth of Metrodata character generators at a CATV head end (2 systems * 4 channels each). They used 6845 Video chips and a 6800 CPU per system on the Motorola Exorcisor bus. There was 48 KB of RAM per system. The C-64 was better quality, and a whole lot cleaner than the Apple II used on our community loop by the local school system. Even with it's 12 line, 22 column display you could barely read it.

But, the C64 had a really bad vertical sync pulse that created a lot of problems for various monitors. It sorta looked like an inverted ramp, with a sharp front edge that then had an exponential curve up to the front porch. I had a sync stretcher that got it to work for my system...

Charlie

flipper:

They do, provided the telephone has a separate power supply. Probably also a supercap, charged while off-hook, would do the trick.

Separate power supply isn't line powered.

Possibly. I haven't looked at the schematics of one but it seems a bit iffy to me that the phone would quit working if you haven't made a recent call.

I should note I wasn't saying he could get it FCC certified. I was just suggesting he might get away with it.

That would probably be a simple divide by 4, the PAL system effectively requires 2 subcarrier bursts in quadrature, using a 4x crystal and a quadrature divider neatly avoids the conventional (semi) analogue approach of shifting the subcarrier oscillator in a PLL.

I remember the loss-leader Jap TVs that wiped out our industry. Some makes had 2 subcarrier crystals, one synchronised to the primary subcarrier and the other to the quadrature phase.

tones

I fed one (SX-64) into a early '50s vintage 25 KW UHF TV transmitter for a video test generator and it looked good on the output of the demodulator. If you had one of the very early units with the white ceramic Video chips with a gold cap, I've heard of problems with those, but they looked like crap anyway. There were several revisions of the video chip over the years.

And you try to tell me PAL was better! ;-)

Well before the Blue Box era, friends had phun with pay phones.

All the upper housing were keyed alike so a repairman needed but one key. The lock of a 3-gonger was a proud Bell System invention, the 10G. So they patented it. And the key. [Or was just the key labeled "10G"; don't recall.]

And that Bell System-wide key was cut *just as shown in the patent filing..*

So they made their own keys. And when Ma had the audacity to raise the price to TEN CENTS; they went around and lowered them to a nickel again...

Nice!

We used to take a wrapper from a stick of juicy Fruit gum, the foil over paper one, put a slight curl on it so it would slide between the base and pay phone. This worked on the older style (1960's era) pay phones. You would slide the foil in on the right side at about the middle then slide it slowly up and down till it shorted out the magic connections. Voila, a dial tone and you could make a local call.

I heard reports of the 'impenetrable pay phone' (early 70's) being deployed at Cornell University. Supposedly the phone had been removed from the wall by the 'inquisitive' folks, reverse engineered and hacks distributed within a day of deployment...

Pay phones in some locations used three wires, the third wire was ground. The ground was used to activate the transfer of the coins from the holding location to either the money box (for a completed call) or the coin return (for a failed call). Open the ground and the money stayed in the holding location. Make your call (long distance even) with the ground open. Pay, then hang up. A few seconds later, reconnect the ground and make a call to a number which you knew was either busy (usually the number of the phone you were at!) or would not be answered. Then hang up and the coins from both calls would drop into the coin return.

It got so the operators would listen for the 'crash' of the coins going into the coin box, and if that didn't happen, they'd ask the user if they heard it! Of course the user always said yes. Later users got smart and had a box that they dropped coins in at the right time, to make the appropriate sound.

I once made a long-distance call with slugs.

Cheers! Rich

I think that's too low tech to qualify for this discussion, Rich. :-)

Somewhere there's a fascinating history of the development of mechanical coin acceptors and all the effort they went to in order to reject slugs and other counterfeit coins. Apparently the clever idea someone had to let the coin fall to hit a piece of metal and then bounce into another slot takes care of rejecting coins that are the wrong pass and even -- to some degree -- the correct mass but the wrong metal.

---Joel

There literally is a company named "Coin Acceptors". Modern mechanisms not only basically weigh the coin, they measure thickness and eddy current "drag" as it goes down the chute. ...Jim Thompson

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The first dollar bill changers around 1964 would accept a single sided BW picture of a dollar bill (Washington's face). Just had to have the right dimensions and approximate paper thickness.

-Bill

flipper:

Gosh.

The caller-ID enabled phones distributed by Telecom Italy have two AA batteries.

Right.

Better than Never Twice the Same Colour anyway.