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Explain bottom.
Well, here is a VCO 555 that is used as clock in one counter and two shift register.
I use some extra circuits to make a speed down counter and make it more real.
Start begin when press on the button located on bottom right.
First click (ON) reset the shift register and start the counter.
Second click (OFF) set the first shift register bit and start the roulet effect.
Hope you like.
Explain:
The 555 (see internet) has many configurations. One of this is as astable. This mode uses one Vref through two resistors and one capacitor. The charge of this capacitor gives to 555 two references through THR and TRIG pines. Inside 555 there are some comparators thar set output to one or zero and open to ground the DISCHARG pin to discharge capacitor. When this happens, output complete a cicle. The internal comparators use Vrefs from +Vcc. Exactly, 1/3Vcc and 2/3Vcc. As capacitor charges from +Vcc too, the frequency is constant (without changing C, R1, R2). If we could change this Vref, we could change the frequency. So, this is what transistor and capacitor do. When you press button capacitor begin its charge up to Vcc while button is on. This Vcc is now the Vref through the two resistors and capacitor. As this Vref is from another capacitor, it is going to down slowly, if capacitor is bigger or faster if it is little value.
Now you can understand what 555 do. It build a clock that is high frequency on start and is going to down slowly while first capacitor is discharging.
This clock is applied to counters to make light effects with leds and 8-seg display.
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