telephone busy light is not right.....

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dacflyer
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telephone busy light is not right.....

Post by dacflyer » Mon Mar 10, 2003 1:29 pm

ok,, i built me a telephone busy light...<p>2 phones phone A & B
1 line...<p>telephone A had the busy indicator,,,so as i was told,,if telephone B is picked up,,then the busy light for telephone A should light up...<p>well not so...the busy light only lights up for telephone A...and if B is picked up..its dead..
this is working like a modem protector sold bu radio shack,,,<p>i need a schematic that will turn on a busy light on phone A if phone B is picked up...whould be a + if it is just something to attach to the lines,,and not something that has to run in series with the phone line...even if it needs to be battery powered,,,if not then thats another plus if its line powered!
i know theres one out there somewhere..please help...thanx !

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Re: telephone busy light is not right.....

Post by greg123 » Mon Mar 10, 2003 2:03 pm

Dac,<p>I am assuming that both phones are connected to the same outlet. What you need is a level sensor. Basically, when a phone is on hook, the line voltage is around 48V and when off hook the voltage is around 10V (this differs in different areas). <p>I copied the following schmatic from an old copy of Nuts and volts in one of TJ's column's. I hope he dosn't mind and hold me in contempt of copyright. :-)<p>Bsically, when the phone is on hook, the line voltage (50V) exceeds the zeener voltage (15v) which causes Q1 to turn on shorting the base of Q2 thus turning it off.<p>I am assuming its what your looking for. The led will light up when the line is in use. <p>Greg<p>Phone in use indicator.

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Re: telephone busy light is not right.....

Post by dacflyer » Tue Mar 11, 2003 9:20 am

thanks for the circuit,, i will make this and give it a try...<p>so,this will tell when a phone is off the hook,
and yes,both phones are on the same line...<p>thanks again !

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Re: telephone busy light is not right.....

Post by greg123 » Tue Mar 11, 2003 1:19 pm

It dosn't matter if the line is in use or off the hook. The line voltage is still the same. This ckt will cork on any phone on the same line (i.e. same number)<p>greg

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Re: telephone busy light is not right.....

Post by frhrwa » Wed Mar 12, 2003 8:34 am

not so about the line voltage being the same.. when you come off hook you complete the circuit from Tip side to Ring side, splitting up the line voltage.. monitoring one side will give a definate drop... Voltages and line currents vary now since the creation of the digital switches.. depending on how far from the C.O. you are, if your behind a pbx, etc..
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Re: telephone busy light is not right.....

Post by greg123 » Wed Mar 12, 2003 12:55 pm

By "Line voltage being the same" i meant that if a phone is off hook, all phones on the same line will be at the "off hook" voltage, around 8-10 volts. I said this, so its not confused where one phone is off hook and at 8 volts, but another phone is on hook at 8 volts as well (not 48).<p>Greg

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Re: telephone busy light is not right.....

Post by lowtec » Wed Mar 12, 2003 7:04 pm

Ok, I'm kinda a newbie.. I looked at that schematic. What is the symbol below R1, with the label 15V. Is that a power source? What should I do with the grounds? Thanks
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Re: telephone busy light is not right.....

Post by dacflyer » Wed Mar 12, 2003 8:27 pm

what you see there is a 15 volt zener dioad<p>and all grounds gonnect together...
easy...<p>
now my turn...lol<p>i made this and it works...
but one question... can i reduce the 2.2k resistor to power a brighter led ? or a blinking led ?
and can i have more than one of these circuits on a line..or is there a limit..was thinking one for each phone...4 phones total....thanx

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Re: telephone busy light is not right.....

Post by gadgeteer » Wed Mar 12, 2003 11:47 pm

I would absolutely go the route of "BRIGHTER LED" rather than lower resistor. No one is s'posed to connect anything to the phone lines anyway; so the lower the drain, the better. If you get a nice 3000-10,000mcd LED, you can reduce the LED power.<p>Less is better...<p>You should also be able to use a blinking LED---but bypass it with a large electrolytic, so that its current drain evens out somewhat (adjust the LED resistor so that the blinking voltage is roughly at rated---do not exceed MAXIMUM...)

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Re: telephone busy light is not right.....

Post by dacflyer » Thu Mar 13, 2003 6:40 pm

i have a super bright led...but it does not get to full brightness...
oh well.. i will be happy with what i have...thanx<p>
but..can i have more than one attached to a line?
like for 2 phones or more?

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Re: telephone busy light is not right.....

Post by greg123 » Thu Mar 13, 2003 8:15 pm

Dac,<p>When you specify a line, do you mean "one phone number". Yes you can one of these at each phone. They will be on if the phone is off hook or in use.

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Re: telephone busy light is not right.....

Post by chessman » Thu Mar 13, 2003 8:54 pm

If you really want to be conservative and not draw 20mA from the line then you can hook a BJT and a 9V battery so the base of the transistor goes to where the anode of the LED was, the emitter goes to ground, the collector goes straight to the cathode of the LED, and the anode of the LED goes to a 480ohm or around there resistor and then to the 9V battery to give you 20mA through the LED with minimal load on the line.

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Re: telephone busy light is not right.....

Post by dacflyer » Sat Mar 15, 2003 7:37 am

chessman >>> BJT ?? whats this? transistor?
advise more please....<p>greg >>> yes 1 line = 1 telephone #
and i have 3 phones on this 1 phone number...
so can i attach one of these devices at each phone with out over loading the phone line?<p>if so...whould it be better to use chessmans idea?<p>[ March 15, 2003: Message edited by: dacflyer ]</p>

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Re: telephone busy light is not right.....

Post by Will » Sat Mar 15, 2003 9:52 am

Something is amiss here - I'm not really a phone man but I'm willing to learn by uttering wrong statements abd then being shot down - I believe that the exchange detects the 'Off Hook ' condition by detecting a current of 20mA or more in the lines ? I did not see the schematic but if you have a 2k2 resistor in series with a 48 volt supply, a 15 volt zener and an LED then won't that produce a line current of 15 mA i.e. (48 - 15)/2200 = 15 mA - So, if you add one more to the line that would be 30 mA. That means that, in order to use more than one circuit, or to use a larger LED, you would have to use Chessman's idea - which looked OK to me Will
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Re: telephone busy light is not right.....

Post by greg123 » Sat Mar 15, 2003 4:33 pm

Dac and friends,<p>Here is the schematic again with chessman's design change. It is the second schematic.<p>Phone In-Use Indicator<p>Greg

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