Wednesday, March 28, 2012 by skemarangkaian
|Water Level Indicator Circuit|
D13 form half-wave rectifiers. The rectified output is filtered using capacitors C1 through C3 respectively. Initially, when water level is below strip L1, the mains supply frequency oscillations are not transferred to diode D1. Thus its output is low and LED1 does not glow. Also, since base voltage of transistor T1 is low, it is in cut-off state and its collector voltage is high, which enables tone generating IC1 (UM66) and alarm is sounded. When water just touches level detector strip L1, the supply frequency oscillations are transferred to diode D1. It rectifies the supply voltage and a positive DC voltage develops across capacitor C1, which lights up LED1. At the same time base voltage for transistor T1 becomes high, which makes it forward biased and its collector voltage falls to near-ground potential. This disables IC1 (UM66) and alarm cannot be sounded. Depending upon quantity of water present in the tank, corresponding level indicating LEDs glow. It thus displays intermediate water levels in the tank in bar-graph style. When water in the tank just touches the highest level detector strip L12, the DC voltage is developed across capacitor C2. This enables tone generating IC1 (UM66) and alarm is again sounded.