For his Amateur radio practice I have collected several schemes calls. The most interesting was a call on the decoder KIT with the melody, programmable resistors. After some time had an idea: "why not develop a scheme call yourself?". Especially houses have accumulated a fair amount of old musical postcards, and there was plenty to choose melody.
The project is not complicated. The call consists of 3 main modules: power supply, circuit retaining button, shawl from cards + power amplifier.
In the scheme used parts: transistors KT315 (4), CT, CT, CTB (2pcs.), diode D, Zener D, diode Assembly, 4 electrolytic capacitor, 8 resistors, relays RAS, mains transformer. The power supply you can use the chip stabilizers on 12 V. it Can be powered by utility power supply and the circuit cards through the quenching resistor. Can be done on the body by two connectors: one for the voltage supply of 220 V, the other for the wires from the button - it's easier to service the call and change the battery in the card. The selection of R2 and C1 can be adjusted the length to play the melody.
Publication: www.cxem.net