My Blog crossed 100000 hits. In this happy moment, I am posting a funny circuit for the kids. This Music Doll gives melody when the hand of the kid approaches the doll. It is a simple Do it yourself (DIY) Project for the beginners who wish to start project building.
When LDR is in light, it conducts and keeps the trigger pin 2 of IC1 high. IC1 will be off. IC1 is a short duration monostable timer with R3 and C1 as timing elements to give 2 minutes high output from IC1. When the shadow of the hand falls on LDR, it ceases to conduct and trigger pin 2 of IC1 becomes low and it triggers. The output from IC1 is around 9 volts which is dropped to 3 volts by the Zener. IC2 is melody generator and gives output when IC1 triggers. T1 amplifies the sound. After 2 minutes, IC1 turns off and melody stops.
Assemble the circuit as compact as possible to enclose inside the doll. Use a 12 volt mini battery (one used in Car lock remote). Place the LDR on the hat of the doll. Use a small Mylar speaker (one used in toys).