re telephone on hook off hok ok circuit in article apr bnr ca moffatt bnr ca john thomson writes just a thought of mine here since an on hook line is aprox v and off hook it usually drops below how about an led in series with a zener say around v on hook led on off hook led off would this work if anyone tries tried it please let me know aye there s the rub if you draw enough current to light an led the equipment at the phone company will think you ve gone off hook in the on hook state you re not supposed to draw current which means you should just use your digital voltmeter you can use an old vom but the phone company equipment can detect that and might think there s something wrong with the cable look guys what s the problem here if you want a light that goes on when the phone is off hook all you need it to run it in series with the line as i mentioned in my previous post if you want a light that goes on when the phone is on hook all you need is a voltage threshold detector if you re going to do the series diode thing which is the easiest just make sure that the led can take the current i can t recall it off hand but it s something like ma or more careful now folks also consider the vac hz that is forced on ring and tip when the phone s supposed to ring even with a simple zener and led setup you might end up with some carbon real quick whatever scheme you use make sure you ve got at least v rated components on the frontend also remember that if i m not mistaken the phone line is a ohm equivalent circuit any current you draw from the v or so gets dropped across that ohms that s fine until you re down to roughly v when ma bell considers it to be off hook but dropping it that far down is probably a big no no the easiest implementation to accomplish the above tip rectifier resistor diode v zener resistor v led ring this is only a suggestion go ahead and blow holes in it but you get the idea choose a high efficiency led so you don t need much current to get it to light up choose values for the other components as required aaron
