42 lines
2.1 KiB
Plaintext
42 lines
2.1 KiB
Plaintext
The following info comes from a leaflet entitled 'FREEFONE':
|
|
|
|
"British Telecoms recent record profits and continuing appalling
|
|
service have prompted the circulation of this information. It
|
|
comprises a method of making telephone calls free of charge."
|
|
|
|
DIAGRAM: PARTS REQUIRED:
|
|
O----o-------o/ o------o----O S1 = SPST Switch
|
|
L ! S1 ! T
|
|
I o--------|<--------o O D1 = 1N4004
|
|
N ! D1 !
|
|
E o--XXXX------>|----o T D2 = L.E.D. (TIL209 etc)
|
|
! R1 D2 ! E
|
|
I o--------||--------o L C1 = 1uF, 250vac non elec
|
|
N C1 E
|
|
O----------------------------O R1 = 2K8 resistor
|
|
OPERATION:
|
|
This circuit inhibits charging for incoming calls only. When a
|
|
phone is answered, there is normally approximately 100ma DC loop
|
|
current, but only 8ma or so is nessecary to polarise the mic in
|
|
the handset. Drawing only this small amount of current is
|
|
sufficient to fool BT's ancient 'Electronic Meccano'.
|
|
|
|
Its extremely simple. When ringing, the polarity of the line
|
|
reverses so D1 effectively answers the call when the handset is
|
|
lifted. When the call is established, the line polarity reverts
|
|
and R1 limits the loop current while D2 acts as an indicator to
|
|
show when the circuit is in use. C1 ensures that speech is
|
|
unaffected. S1 returns the telephone to normal when closed.
|
|
|
|
With the phone on the hook this circuit is undetectable at the
|
|
exchange and/or on the line. The switch should be closed to make
|
|
outgoing calls and when receiving calls from the operator.
|
|
|
|
The method illustrated here uses the same technology that BT use
|
|
on their 0800 exchange to obtain free incoming calls. (Try this
|
|
number as a demo: 0800 800 800.)
|
|
|
|
*****DO NOT DIVULGE YOUR SOURCE OF THIS INFORMATION*****
|
|
|
|
|