Fast switching DEL display, persistence of vision verification
This project shows a control circuit used to produce short pulses. When the key is closed, the table LED is lit momentarily, even if the key is kept closed.
This circuit can be used for a game where a number or letter is displayed momentarily, and players must attempt to recognize the number or letter. You can spell words or give numerical responses, etc. You can probably think of a lot of possibilities.
The transistor switching circuit uses the charging current of the capacitor to switch the transistor on. The transistor then completes the circuit to the anode of the LED pins. When the key is open, the capacitor is discharged by the two resistors of 10K.
Then, when the key is closed, the capacitor is charged 3.3 uF quickly up to 9 volts across junction B-E activates the transistor full function only during the time that the current passes. The power transistor is as a short circuit from C to E to permit current to pass LED simultaneously with the charging current of the capacitor.
After the capacitor is charged up to 9 volts, there is more current which can pass junction B-E of the transistor when the transistor is completely stopped.
Audits by VOM does not clearly demonstrate the action of the circuit because of the short period of time during which the circuit parameter change. One thing that is remarkable is that a measurable amount of time must be allowed for the capacitor discharges after the key is opened.
You may want to try different values of capacitors and see their effect. Do not use capacitors whose value exceeds 10 uF because the transistor for would be grilled by the basic excessive current. Of course, you'll want to try different numbers and letters on the LED, especially if you play the game of persistence of vision check.