Telephone On-Hook Current

"Errant", maybe, but it sure was a lot of fun.

Our first not-quite-legal phone call came from MF created from a Fender organ. I can't recall how we generated the 2600Hz. We got more sophisticated after that with real oscillators.

We sure had fun - as did Jobs and Wozniak (from what I read).

Bob

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One of Wozniak's claims to fame was that his blue box generated all the tones digitally.

He became quite good at abusing digital chips for analog purposes -- he did similarly creative/ugly things when generating (NTSC) color on the Apple II, adding almost no cost to the design in the process. Such a feat was largely unmatched for years; it was really only complete graphics ICs like the Commodore VIC and perhaps the Motorola 6845/6847 that -- eventually, as volumes increased and prices dropped -- outperformed Woz's approach on a price/performance basis.

---Joel

Did you ever look at that Apple II video on a waveform monitor? The ones I saw were nasty. The C64 was cleaner than some low end (

Why not use an analog voltage comparator to monitor the voltage on the phone line? That would keep the load in the uA range.

--
You can't fix stupid. You can't even put a Band-Aid? on it, because it's
Teflon coated.

Takes power to run the comparator. Though it does look feasible to use a battery. I can think of at least one configuration where power consumed from the battery would occur only for a few seconds each call. ...Jim Thompson

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| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |

      Remember: Once you go over the hill, you pick up speed

Use a wall wart. Even better, use one with +/-12 outputs. Small switchers are dirt cheap, or even free if you have a well stocked junk box. It would also provide the power for your relays and such.

--
You can't fix stupid. You can't even put a Band-Aid? on it, because it's
Teflon coated.

You've got RING POWER that you can harvest, and you're trying to fiddle around with stealing microamps during on-hook? Once again, a WPI grad has to jump in and help an MIT guy with the practical stuff. Jeesh*.

I'm not getting my book out for you again. Look up CFR Title 47, part

68, whatever subsection specifies how much a conforming phone can draw for a ringer -- it's huge, because it's designed for a bell. You'll be seeing something like a 20Hz, 100VAC (maybe 75V) sine wave, and you can draw as much current as a Freaking Loud Electro-Freaking-Mechanical bell draws and be OK. There ought to be enough Joules available at the end of the first cycle of that to calculate pi to 100 decimal places.

Then you just need electronics that can come awake fast enough to read the caller ID and make whatever decisions you want to make.

• :-)

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Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html

What happened to Ma Bell when she backed up into a meat grinder?

Disaster.

-Bill

flipper:

If you are connected to a private PABX, not to a central office.

Here in Italy the maximum resistance tolerated is about 4 M. Lower resistances will trigger an investigation on circuit losses.

F. Bertolazzi:

Minimum, clearly.

In the US should be 5 Megaohms.

Here, the current loop indicates off hook.

How does your central office detect off hook?

I guess your regs don't allow line powered phones with caller ID and phonebook dialers

I still look back with a smile on how the public utilities were mandated to have technical documents on file in certain libraries. I know that here in New York, the Ma Bell stuff was on file at Cornell University and Clarkson College (where I attended). Both campuses became active phone phreakery sites. You'd think the bigwigs would have put the documents in a liberal arts school rather than engineering schools...

At the point when the phone company moved to electronic switching systems, tracking of theft of service went into high gear. Most of the 315 area code (Northern NY) was configured to put a hold and trace on any circuit (outside of legitimate ones) where a 2600Hz tone was detected. In an interesting twist of fate, my daughter re-married and her father-in-law is a retired phone company investigator who was involved big-time in hunting down phone phreaks. Nice guy, very smart and I'm very happy that I never had a chance to meet him in his official capacity...

Oppie

I'm watching the pass-thru port on this call blocker...

At t = 0-, all you see is the typical ~45VDC

At t = 0+, that voltage goes away because the call blocker disconnects that port for the duration of the first ring... that's what I want to detect... that drop-out of ~45VDC.

I see no ringing voltage on this port until the second ring. ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |

      Remember: Once you go over the hill, you pick up speed

"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...

Strip out a few old speakerphones - the one's that don't have a battery compartment often have a high voltage-very low current inverter to maintain the supercap at a much lower voltage.

AFAICR the PAL standard Commodores used a 4x 4.433MHz crystal with a quadrature divider to avoid a lot of complicated analogue stuff.

Ah -- I misunderstood. I thought you were _building_ your own call blocker for some reason. Does it make sense to tap into the incoming line, just for ring power?

--
http://www.wescottdesign.com

No, but from Woz's description of how it worked, I'm not surprised. Even he says he wasn't sure it would really work on all TVs!

But for a hack that didn't cost much of anything, it's still quite clever.

The first computers I used were Apple II's and Commodore PETs (before the C-64 came out), and honestly... I'm amazed Commodore survived its PET era to go on to make the (very good) C-64 -- compared to the Apple II, the original PETs were quite crude. (...and the story goes that this was even after Chuck Peddle had talked directly to Woz and knew a lot of how the Apple II was being designed. Although, on the other hand, Peddle deserves a lot of credit for realizing that a cheap CPU would completely revolutionize the industry...)

I find the entire history of the 8-bit computer industry quite fascinating -- it really demonstrated how a few smart guys (most of them without college degrees) created widgets that were years ahead of what much-better-funded large companies such as HP, IBM, Wang, and so on could cook up.

They did it "properly" (in the VIC-II) chip by taking their 14.318MHz crystal oscillator, generating quadrature signals at 3.58MHz, and then adding in various ratios of I and Q to get the desired phase shifts. Their hue (I/Q or U/V), then, ended up as the ratio of a couple of on-chip resistors -- quite decent -- but their intensity was a function of an on-chip resistor's raw value -- kinda crappy. The story goes that Commodore was too cheap to let them add, e.g., an external 1% resistor so that intensity could be reasonably accurate as well:

---Joel

Great story. Did you ever discuss your escapades with your daughter's father-in-law? I would have loved to have seen his face.

We started goofing around after the famous Esquire magazine article was published with its interview with Capt. Crunch. We didn't have access to any official docs, but the book "Basic Telephone Switching Systems" was all we needed to build the blue boxes. I still have a copy of it.

Besides blue boxes, I built this thing labeled a "black box". It worked with incoming calls and would simply create a momentary offhook condition and then cap couple the phone to the line. Its effect was that the calling party would not get billed, but the two ends could talk. I'm not sure why it worked because there was no loop current to power the carbon mic.

Bob

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