phone light problem

You cannot just go hanging an LED/resistor across the phone line and expect it to not interfere with the normal operation of the phone line. Using an LED and 100 ohm resistor, such as you asked about, would most likely make the line appear as off hook at the central office.

In my suggestion I would recommend that you run multi-pair cable (telephone wire is common with 2 pairs and sometimes 3 pairs). Then setup a second pole on your switch to switch a low voltage DC onto an extra pair with which to light your LEDs at the telephone locations. Use a low cost wall wart type device at the switch location to energize the pair for the LEDs. You could even re-purpose an old cell phone charger or a 5V USB hub power supply.

--

Michael Karas
Carousel Design Solutions
http://www.carousel-design.com

--- TPC takes a dim view of anything using its 48V to power non-TPC stuff, so here's what I'd do: (View using a fixed-pitch font)

TELCO T/R -----O |S1A | PREMISES WIRING

TELCO T/R>-----O |S1B | PREMISES WIRING V+ \ +--------O +-[R]---[LED1>]--+ |+ |S1C | | [BATTERY] | ]--+ | | +-------------------------------+

This way your LED circuitry is completely isolated from TPC's lines.

S1 is, of course, a 3 pole single-throw switch

Instead of a battery you could use a wall-wart or any other DC supply, and to figure out the values of the resistors you go:

(V+) - Vled R = ------------- Iled For example, if you had a 9V source and a red LED which dropped 1.8V with a current through it of 20mA, you'd have:

9V - 1.8V R = ----------- = 360 ohms 0.02A

and the resistor would dissipate:

P = I²R = 0.02A² * 360R = 0.144 watt

360 ohms is a standard 5% value and it's available in a 1/4 watt size, so that would work.

-- JF

100 ohms would make the CO think the phone was off-hook, and the ring signal would blow out the LED.

A high-efficiency green LED will be nicely visible at 50 uA, so use a

1M resistor. A couple of those circuits won't disturb the phone line.

A fancier circuit could charge a cap at, say, 1 uA and blink the LED at 1 Hz or so. Probably not worth the trouble.

I tested some good green LEDs once. They were clearly visible in indoor lighting at 1 uA, and, dark-adapted, I could just detect visible light at about 0.8 nA.

John

Use a little brainpower...

1) I = E/ R; I = (48V)/(100 ohm) = 480mA (!!); wy too much - useful to fry the LED if the source had lo internal R. 2) Massive loading like that will be the same as of a phone was off hook. 3) Are you trying to imply there is an _AC_ LED??

Pick a high luminance at low current LED and run it at 100uA (there are some blue ones and some white ones that are quite bright at that current level); this loading might be acceptable.

...and 20mA is WAAY to much current; most decent LEDs are rather bright at 1mA;many at 100uA. Lower power drain on the poor 9V battery will allow it to last longer.

I built a really basic "LED Analyzer" for Instructables.com a while back, and nearly blew out my retinas testing some random "super-bright" green LEDs at mA currents.

What was the forward voltage at 0.8 nA? The circuit I used would have to be significantly modified to get accurate results at such low currents.

I have a friend who runs the LED lighting division of Hubble. He gave me a multi-chip white LED thing, about the size of a quarter. At 12 volts, half an amp or so, it looks like an arc welder.

1 mA is plenty for a good LED on a PCB as a test indicator, like on a uP port pin. We like the Osram surface-mount parts, nice colors and they hold up to soldering.

I don't recall; it was dark, so I didn't take notes! I used a bench power supply and various series resistors, 10G ohms max I think.

John

I have a Tadiran 3 A-H lithium battery connected to a good green LED through a 1M resistor. It will outlast me.

John

--
You must have missed that instead of giving a man a fish I was
teaching him _how_ to fish.

--
Hopefully, then, it'll burn out soon . ;)

100 ohms would make the CO think the phone was off-hook, and the ring signal would blow out the LED.

A high-efficiency green LED will be nicely visible at 50 uA, so use a

1M resistor. A couple of those circuits won't disturb the phone line.

A fancier circuit could charge a cap at, say, 1 uA and blink the LED at 1 Hz or so. Probably not worth the trouble.

I tested some good green LEDs once. They were clearly visible in indoor lighting at 1 uA, and, dark-adapted, I could just detect visible light at about 0.8 nA.

John

=============

Using this formula to select the right current limiting resistor,

I tried a 2.2k but the phone wouldn't hang up. So I tried a 5k resistor on each of 2 LED's and it worked ok. I had my buddy call me. The LED's lit up brighter when the phone rang but didn't burn out. Just in case of power outages I'm using this circuit. I'm also going to try 1M as suggested so the LED's last longer. That way the circuit won't be dependent on the electric company to operate, even though that wouldn't be much of a problem if when the power is out the circuit uses N.C. relay contacts.

Pesky creditors. I'm going to block them out all together. I can't get any sleep on account of the phone ringing all morning. My girlfriend has fallen behind, not me.

[snip]

Rated? I've used old-fashioned (beefy) automotive starter relays to run golf carts at 300A+ for my Sun City hot rods... golf carts run on city streets. Never had one fail. ...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     |
             
I love to cook with wine.     Sometimes I even put it in the food.

The circled 'A' at the bottom looks like an amp meter!

--- Posted via news://freenews.netfront.net/ - Complaints to snipped-for-privacy@netfront.net

Yup. Sometimes you have to have an open mind about other people's symbology, though.

The circled 'CR1' in this illustration could be a diode, if you squint, too.

The text says it's a relay coil, though.

++++++++++++++++++++++++++++++++

From "Surely You're Joking, Mr. Feynman!" ISBN 0-553-34668-7

"I'm completely dazed. Worse, I don't know what the symbols on the blueprint mean! There is some kind of a thing that at first I think is a window. It's a square with a little cross in the middle, all over the damn place. I think it's a window, but no, it can't be a window, because it isn't always at the edge. I want to ask them what it is.

You must have been in a situation like this when you didn't ask them right away. Right away it would have been OK. But now they've been talking a little bit too long. You hesitated too long. If you ask them now they'll say, "What are you wasting my time all this time for?"

What am I going to do? I get an idea. Maybe it's a valve. I take my finger and I put it down on one of the mysterious little crosses in the middle of one of the blueprints on page three, and I say, "What happens if this valve gets stuck?"

-- figuring they're going to say, "That's not a valve, sir, that's a window."

So one looks at the other and says, "Well, if that valve gets stuck --" and he goes up and down on the blueprint, up and down, the other guy goes up and down, back and forth, back and forth, and they both look at each other. They turn around to me and they open their mouths like astonished fish and say, "You're absolutely right, sir." "

--Winston

The symbology in this thread seems to be derived from Wade Instruments web site and since they are a 13 year old SOFTWARE company the symbols could hardly be described as "Industry Standards" or anything like most of us have come to understand. Just another example of Jon's lack of understanding of electrics.

Interestingly the relay in the Wade tutorial above does not seem to have a key on the spigot so could be inserted any way you like with obvious unpredictable results.

--
John G

John G commented:

site and since they are a 13 year old

or anything like most of us have come to

The Ladder Logic prima facie industry standard is older than that. The PLC host apparently dates back to 1968:

Though I do see that the existing industry standard was formalized much later (IEC 61131-3 1993).

Have a look at the top of page 6. This looks eerily familiar, yes?:

(...)

on the spigot so could be inserted any

The relay is keyed using a bump on the 'octal' socket center pin. Look between pin 1 and pin 8:

--Winston

Just to be clear, there are at least two of us posting under the name Jon....

--- Posted via news://freenews.netfront.net/ - Complaints to snipped-for-privacy@netfront.net

Jon clarified:

(...)

Yup. snipped-for-privacy@bellaire.tv is the OP.

You (Why_bother@this_task.com) first brought up the documentation issue.

--Winston