|
In this sequel to my 7-segment Power Bank circuit, I've rigged up an interesting little oscillator.
To make it go, flip the SPDT switch up. Then, flip it back down. Current will now flow back and forth through the inductor and in and out of the 7-segment display. Crazy.
Actually, the concept is pretty simple. The 7-segment display contains hidden capacitors. By adding an external inductor, I've created a resonate tank circuit. This tuned LC circuit will oscillate at its resonate frequency, causing the display to blink ON and OFF.
We can actually calculate the capacitance of the 7-segment display if we know the resonate frequency and the inductance.
C = 1 ÷ (4 × π² × f² × L)
C = 1 ÷ (4 × π² × 1260² × .02) = 800nF
For the very observant, you will see a rather strange relationship between the voltage, current, and light in the display. The display lights up when the current is flowing into the device. But, due to the interaction of voltages and currents in an LC tank circuit, the current and voltage are out of phase by 90. This puts the display in a very odd state where the current through it and voltage across it are not directly proportional. See how when the current is at a maximum, the display lights up, but the voltage is near 0V? I guess this proves that the light in an EC LED is based on the amount of current, not voltage.
Prequel circuit: https://everycircuit.com/circuit/5861787383365632
This trick can be done with 2 LEDs also. https://everycircuit.com/circuit/4699313716068352
|
