On 2007-02-15, Chrom_ wrote:
Jasen,

there's no need to butcher the phone:
make a vibration sensor and set the phone to vibrate, or a light sensor and
detect the display lighting up when it rings.

I don't mind slaughtering the phone if I can save money :-) It's old
and useless as it is now. I could attach the relay directly to the
vibration motor, but in this case I nees an accumulator before the
relay switch. How do I decide the size of the accumulator and of the
relay?

if the phone is charged from an isolated source
(ie not from an earthed source like USB or the pc's powersupply)
you don't even need a relay. this circut will do it:

it's probably best to use the led for the signal as hopefully
it won's switch on and off many times retriggering the power
switch,


you'll have to get it the right way round both ends.
if you have a voltmeter the more positive terminal
is top both ends, if not it won't be damaged
if connected backwards


.------ to power switch
10uF /
+|| |/ BC547 /
----+-----||-+--[1K]----| (or 2n3904 etc)
| || | |\|
from LED [100K] -+- ~\
| /A\ 1N914 |
| | |
-----+--------+------------+------

(needs to be viewed with a fixed font
hit view source under options to align the text)

Bye.
Jasen