Circuit Project Electronic

Most of the telephone security devices available in market are simple but quite expensive. These devices provide blinking or beeping type line-tap/misuse indications. Quite often they do not offer guaranteed protection against unauthor-ised operation. A very simple and uni- que circuit of a telephone watch-dog to safeguard subscriber telephone lines against any fraud is described [...]

Toy Organ By IC Timer 555

Circuit : Andy Collinson
Email: anc@mitedu.freeserve.co.uk
Descriptipn:
A switched timer for intervals of 5 to 30 minutes incremented in 5 minute steps.
Click to View Circuit
555 Timer 5 to 30 Minute

Notes:
Simple to build, simple to make, nothing too complicated here. However you must use the CMOS type 555 timer designated the 7555, a normal 555 timer will not work [...]