555 toner circuit 2.0

This circuit is a toner (without the worble because i only have so much space to build in this app). There are multiple power sources shown yet only two power sources in reality. All the 10v sources are just the positive terminal of a battery. The 50v source is "Talk Battery" or voltage from the telephone service provider. The 555 puts out an oscillation. The oscillation goes to base of BJT and the BJT will act like a switch on and off repeatedly. The diode above the BJT hooked up to Vcc(the battery / the 10v source) is there so that if the toner probe is hooked up to a source that is 10.7v (Vcc plus diode brrak down voltage) or more, the diode is biased in a manner that it will not conduct therefore the BJT will be sinking current off and on from the telephone line allowing for a swinging voltage to be present on the line that can be picked up with a tone probe. The op amp and its associates circuitry detects wether there is a small signal on the line (tone generation from 555) or a large signal on line (off and on sinking current from telephone line as source). The opamp will trigger a relay to switch between two modes of operation for the bjt. So pretty much if high voltage is senses the op amp knows to switch the toner into sink mode. If low voltage is sensed the op amp knows that the user has not hooked up the toner to a live line so the user wants to tone a inactive or dead or open line. The switch on the far right above the 50v power source represents the two situations; probe hooked up to 50v source from telephone line or probe hooked up to open / inactive line. You will see the LED as a visual aid to let you kniw that current is being SOURCED during open / inactive line mode. I may add reverse polarity detection as it would only comprise of a Fet and a few resistors etc. But for now this is the circuit.

published 8 years ago