i've tried this diagram, and it's ringing all night. sun up alarm can detect light in a dark area, but even if it is dark it keeps on buzzing. this is our project, and we need help badly. i dont know what the problem in our circuit.
The photo-transistor is supposed to be turned off (its emitter less than 3V) when it is dark. Yours is turned on (its emitter is more than 6V). Check its pins then replace it.
the longer one in my phototransistor pinned in the ic which is pin 1. and the the shorter one is connected to the vcc. i used wpt-440 ?? the one that sells it told me it is a phototransistor
You should have looked at the datasheet for the WPT-440 IR photo-transistor.
It is most sensitive to infrared light, not ordinary visible light.
Its datasheet has a photo showing its pins. Both pins are the same length.
Maybe you connected its pins backwards. Maybe you have too much infrared light when it is dark.
The 300k resistor at the input of the first Cmos NAND gate to ground keeps the oscillator turned off when there is no light and when the photo-transistor is removed.
NAND: BOTH inputs must be high for the output to go low. If ONLY ONE input is always low (by the 300k resistor) then the output is always high. If ONE input is always high (by light on the photo-transistor) then the output is the opposite logic to the other input (which is part of the oscillator).
Maybe your power supply filter capacitor is missing and is causing severe ripple.
what if i want the circuit to buzz at night? do i have to use another LDR as an input and a LED to be its output, so that it will not buzz in the daylight?