duplicating phone and ring voltage

[mm]

I need to connect some telephone-type things together in my own little circuit, and test them, but I don't know a simple method or what voltages to use. I think I need to use some wire, some kind of DC power, something to put a ring-signal on the line, a phone, and whatever I am testing.

For example, I'm getting a replacement for my all-time favorite phone answering machine, but the owner has forgotten the 3-digit code for remote message retrieval. :( I'm willing to try all 900 or 1000, probably while I'm watching tv, but only if I can get it to go quickly. So I need a test line to ring it directly, have the machine answer, and punch in the code.

Also I have 2 fax machines, one that sends and one that receives! :) I'm pretty sure I can get it down to one that does both.

I don't have two phone lines, and even if I did, I think things would run quicker with my own little circuit.

In the 7th grade, we had two candlestick phones and a dry cell to play with during ham radio club, and everything worked (except it didn't ring, but that was ok because they had no bells. :) )

Any help appreciated.

[JANA]

Phones need 48 Volts DC with an in series of 600 to 800 ohm source. The ring is 96 Volts at 25 Hz.

For the answering machine, if it is a name brand, you should be able to get the information about how to reset the remote code. If it is a fixed uninique code, then you have a problem. For what it is worth, maybe it would be better to simply get a new answering machine.

[Kevin Ricks]

Are you sure you can't just program a new access code without knowing the old one? My machine does not ask for any codes at the base unit for anything. The new code just replaces the old. Only remote access requires the code. But yours may be different.

Kevin

[hallerb]

there are little circuit boxes that immitate the phone line, last I saw one about 60 bucks

[Michael Kennedy]

Thats the way to go... Getting the operating voltage (48vdc) isn't that hard just hook up 4 12 volt batteries in series with an 800 ohm (If I remember correctly) reisistor on the end. Getting a 20hz ringtone is the difficult part since the wall current is 60hz.. I never figured out an easy way to make my phones ring.

- Mike

[Tony Hwang]

Hmmm, In this digital age, playing with analog?

[Dave D]

There's several easy ways to generate a 25Hz at 96v, one is an old fashioned multivibrator driving a 120V/12V transformer secondary, (ie a 25Hz inverter) and adjusting the multivibrator's supply down to get 96V. It's rough and ready but there's no reason why it shouldn't work, and it uses a few standard, off the shelf components.

Dave

[Jay]

snip

Jana:

Seems like a lot of effort for short money (bad ROI)?

What Make and Model is this unit?

I bet we could find you one on e-Bay that doesn't entail hooking up multiple

12 volt batteries in series and punching in a possible 1,000 codes to get it to work!

Do you really want to sit amongst multiple car batteries in your living room watching TV punching in codes all night and then recharging them, trying

1,000 possible codes is going to take some time and will probably require one, or more, recharges.

Just my $.02 worth. Voicemail!!!!

Jay

[Beachcomber]

Yup... It's called POTS Plain Old Telephone Service.

One thing to consider... Many fax machines and other devices have dial tone detection circuits. The mere presence of DC voltage on the line will not make them dial. Also, getting the correct 20 Hz ring frequency and voltage (with the right current) in a home grown circuit is a pain unless you are willing to get fairly elaborate.

Here is a fancy Ringdown Circuit from Viking Electronics. List price is $106

Beachcomber

[spamTHISbrp]

Black magic ring generator-

Dave

[Dave Plowman (News)]

That's the spec to allow for vast voltage drop over the miles of cable between phones. Just to get two to talk to one another 9 volts will work just ok. Indeed if you're talking about old non electronics phones with carbon mics 1.5 volts will be ok for short runs.

[Ken Layton]

Try the Viking Electronics model DLE200 telephone line simulator box. It's only about 5" by 2 " with phone jacks on it. It only cost around $100 about 12 years ago.

[mm]

Thanks a lot.

It is a fixed code. A friend of mine and I each bought one 21 years ago, and the code was printed on the box, not on the bottom of the unit that became more common. I wish it had been on the bottom; we would still have it! This new one is from the wife of a friend, and she stopped using it a couple years ago and has forgotten the code. :(

It's Code-a-Phone, model 2530 or similar model.

Like I say, this is my all-time favorite phone machine. I have about

10 others, all different brands or models, that I've bought in the last 2 or 3 years, paying 1 to 3 dollars each at hamfests. They all work as designed but I don't like how they work.

[Bill Janssen]

I have always used the assumptions that there was 400 Ohms in the telephone. The telephone wants

20 milli-Amps or more so that says you need 8 Volts or more (per phone) The 48 Volts (really 52) that the central office uses is to push at least 20 milli-Amps through the longest line.

Bill K7NOM

[jimmiedee]

I used to have a hand cranked generator from an old phone. This puts out exactly what you need. Think they are still available through gov surplus as field telephones.

[mm]

We had these in that 7th grade class I mentioned, but I don't think they lend them out (and may not have them 46 years later :) and I live in another city) But I'll look in surplus sources. OTOH, this will slow down some my prospective 15 seconds per code, that I need to finish in about 2 hours. Thanks.

Thanks a lot to you and beachcomber. It is just what I need, and the price now ranges from 145 to 114, for the very same thing, online, plus shipping. It's small to -- oh, yeah, you said that -- and although that is a lot of money to fix these two things, it may have uses in the future. OTOH, I have the specs now to do this myself, so we'll see.

>

[Rich256]

Try ebay & search for crank phone or something similar.

[Michael Kennedy]

Wish someone had told me that when I was trying to build a ring circuit.

Oh well I guess I know now. :-)

- Mike

[Ross Herbert]

Since you need to find the 3 digit code for message retrieval it is not simply a matter of generating the correct ring signal. The ring signal needs to be received and tripped so that a normal line connection is established with correct DC potentials etc. Only then can you send the DTMF signals to the fax to determine the 3 digit code. For this you will need an analog phone line simulator similar to

Unfortunately these aren't cheap (US495 for the TLS3).

AN Australian device which will do the trick is shown here

and sells for around USD271 plus postage.

In the UK you can buy a kit to build one

will be a lot cheaper than the Teltone.

[Ken Weitzel]

Hi...

I'd be willing to bet that if the OP would disassemble the machine he'd find the code on a label somewhere inside it.

Take care.

Ken