In this exercise, the focus in on learning how to use Programmable Unijunction Transistors, also known as PUTs. With the ‘belly’ of the transistor facing your right, the top leg is the anode, the middle is the gate, and the bottom is the cathode.
What makes PUTs different from the previous transistors in earlier projects is that the anode must be ‘more positive’ than the gate in order for the power to go to the cathode. Say, if the gate had a 2k2 resistor and the anode a 50K resistor, no power will travel to the cathode. No power is traveling because the gate has ‘more power’ than the anode. The gate is blocking energy from travelling to the cathode.
By adding capacitors in parallel to the anode, enough ‘power’ can be collected that the anode will eventually be ‘more positive’ than the gate, which causes the capacitors to discharge and send power to the cathode. The cathode is connected to an LED, which lights up until the power level in the anode drops below the power level of the gate.In theory, this process acts like a timer which flashes an LED. Keeping the capacitor the same, the LED can be made to flash faster by decreasing the resistance in the anode or increasing the resistance in the gate.