NE555 Timer Tester Schematic

In this 555 tester circuit voltage is supplied in DC by a 9V battery. This battery charges up the capacitor (C1) which is monitored by pin 6, the threshold pin, once this capacitor reaches 2/3 VCC, it will discharge to pin 7, the discharge pin. Voltage is also supplied through a resistor (R3) to pin 7 which is done so pin 6 can compare the voltage of the capacitor to VCC and essentially decide whether to discharge or recharge, (discharge if > or equal to 2/3 VCC or recharge if < or equal to 1/3 VCC. Because two resistors of equal value are used during charging and only one is in use while it is discharging, we will have twice the resistance while charging than when discharging. (A diode could be used here so that both directions have the same resistance). Pin 6 is connected to pin 2,(the trigger pin), so that when the capacitor is around 1/3 VCC it will be low enough to trigger pin 2, thus completing the circuit and telling the 555 to begin recharging the capacitor again. The output of the circuit, from pin 3, the output pin, is measured with two LEDs that will turn on when the circuit is completed with the button, and flash when the button is held, (due to the Astable nature of the capacitor that is discharging and charging). Also on the schematic a diagram, a 555 timer was used, but as the purpose of this circuit is to test if a 555 timer is functioning, a 8 pin base would be used here instead so that the timer could be interchanged and therefore tested.