Still more stories about Neon lamps: Experimenting as a kid (35 years ago or so), I hooked one (an NE-2) directly across a telephone line as an indicator for the ring signal. It worked "kinda". Turns out that the AC voltage of the ring caused the bulb to strike, and since I didn't have a resistor in series, the current of the strike was enough to signal "answer". Then the central office returned the supply voltage to the normal 48 volts, and since this was below the keep voltage, the bulb went out and with no current, the C.O. thought the phone was hung up. The other extension phones had a short ring. The caller heard little. You had to run to the phone and answer it if you wanted to talk. It makes for a very annoying trick! The solution to this is to add a resistor (about 51k as I remember it) in series. The current drawn when ringing thru the resistor isn't enough to make the C.O. trip answer. Now fast forward a bunch of years, and I work for a company that uses neon-CdS "optical isolators" to detect ring. They DID put the reisitor in series. The problem then happened that they forgot to put a capicator in series as well. Normally this doesn't make any difference, but in some areas (mostly rural) the voltage is raised to make up for long line loss. Sometimes it is raised to over 90 volts. In some of these situations the indicator would always indicate "ring". It wasn't too good. Now days we use optical isolators and a series R-C combination. It works pretty well. You need a reverse diode across the optical isolator (an LED works well, and makes a good indicator) so the cap won't take on a DC bias. p.s. 4 layer diodes work like neon lights (different strike/hold voltages) but a lower voltages. An X-Y matrix similar to the neon ones discussed would work, but with no visual readout. These were proposed, but IC's came into being, and the hassel wasn't worth it. Oh, well. __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com