uucp@iuvax.cs.indiana.edu (02/10/91)
This off-hook indicator is LINE POWERED. I've made one of these and it works; I recommend socketing the transistors (augat pins are perfect) as I've had awful luck frying them with the soldering iron (even though it's temperature controlled @ 700F). No warranties express or implied, build at your own risk, etc. +---------------+------------+----------+----|<------o POS side of phone line | | | | | | V | D1 | \ - LED | | / R3 | | C1 .01uF 200V | \ | | D1 1N4003 or greater | / / c | LED an LED \ | |/ | Q1,Q2 PN2222A * / R1 +-----+---------| b Q3 === C1 Q3 2N5551 \ Q1 | | Q2 |\ | R1 470K / / c c \ \ e | R2 20K | |/ \| | | R3 47K - 100K +------| b b |--------+ | R4 100 ohms | |\ /| | | \ \ e e / | | * 2N3904 or 2N4124 / R2 | | \ | also suitable \ | | / R4 | / | | \ | | | | / | | | | | | +---------+-----+-----------+-----------+------------o NEG side of phone line Interesting "polite" phone modification: to line ------------------------------------------ to phone TIP relay * | <-+ | - | - - - +-CCCCCC-+ | | | | RING to line -----o o-------+---|<---+-------------- to phone | | | D1 | +v v+ | | ---- +---|(---+ 'on' button + C1 D1 is a 6.8v Zener diode. C1 is an optional 680uF or greater electrolytic capacitor used to prevent call waiting from dropping the connection. The relay should be in the neighborhood of 2.2K ohms with a 6V coil; the contacts should hold to around three volts. On button is a standard NO pushbutton. When this device is wired in-line with a phone, depressing the "on" button will cause the phone to go off-hook, where it will remain until the switchhook button is pressed. It is most effective in a trimline-type phone, especially the one in the bedroom; since the phone no longer needs to be placed into its cradle, it can just be tossed up onto the headboard (or wherever). Very convenient if you're horizontal. I haven't actually made one (lost the relay somewhere), but I've seen one in action.