Here is a pleasant wake up alarm for the babies. As the morning light breaks in, the alarm gently wakes up the baby with a soothing musical note. What a pleasing way to make the baby rise to the day!
As already described, LDR has a very high resistance in darkness, which falls low as the light falls on it. Hence Ql does not conduct in darkness, as it is reverse biased by VR1. As the daylight breaks Ql goes into conduction and powers UM66 musical IC. Musical note at its output is amplified by Q2 and is fed into the 8-ohm speaker.
There a number of UM66 T chips, each giving a different note. You may also add a suitable voice COB like a sloka or a prayer in its place. The circuit is shown in Schematic 32.
You may use 3V with dry cells as the power supply, but operation at 3.6 V is good. It is better to use three or four Ni Cad or Ni Mh cells as they can be recharged and reused. Straight forward construction on a Vero board is all needed. Use plastic battery box available in the market to fix the batteries. Adjust 220k preset to the desired sensitivity, thereby at the required intensity of daylight, when the alarm should start singing.
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