The rectified voltage from the rectifier diode is not constant, because by a sine form and also from the tapped voltage of direct current affected hum. By installing a capacitor (usually elco) between plus and minus, the hum voltage will be reduced, this is because during pauses hum voltages, the capacitor provide the current and during each half period its will be charged. Hum voltage is determined by the capacity of the capacitor and current are used, it is according to the following rules:
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The easiest way to calculate the buffer capacitor
LDR Measurement and Testing
Measuring and testing the LDR sensor (Light Dependent Resistor) is very easy to do. As we know, this electronic component is a resistor whose value will change according to the intensity of light received by the surface of LDR circuit. So, when doing testing, you need to compare the resistance value of LDR, between the moment when light and dark.
How to test LDR:

