J.E.Lawrie HINTS-CT Low-Voltage Indicator Circuit and LED positioning. ( for description - see HINTS-21 ) Battery +ve _________________________________________________> | | | | | | > > < < > 220k > 4.7k < < | | | | +ve |___________b c_______|__________________________ | | | NPN e a > transistor| LED 3mm Red < | k > 47k pot. | _________________________| < | | -ve | | | | | | > | | < | | 1/6 watt resistors > 22k | | < | | | | | | | | |______________|_______|_________________________> Battery -ve OPERATION. The transistor conducts, shorting out the LED, until the voltage across AC is 4.4 volts and across BC (by prior adjustment of the pot.) is less than 0.6 volts when the LED lights. Resistor values are not critical. Max circuit current - <1.5 mA LED Positions :- Green Red ____________________________________________ | | @ represents LED. Slot 3 | @ LED centres - 4 mm @ | | down. | Positions are ___________|_______________________________| important to avoid > < > < difficulties in 4 mm 15 mm fitting the LEDs. Back to HINTS-INDEX, HINTS-21