Light NeoPixel with 555 Timer IC (Part II)
To continue the discussion from Part I, the design goal is to generate BIT-1 for NeoPixel with 555 IC.
The following is another 555 astable circuit uses only one pair of RC, and it outputs equal high time and low time.
It can be analyzed using that RC step response equation (see Part I of this article).
Although VF, VT and V0 take different values for charging and discharging of the capacitor, the left hand side end up being the same value:
So the pulse width Δt = ln2 * R1*C1 = 0.69 * τ
With R=1.8k Ω and C= 330pF chosen, τ = 0.6μs and Δt = 0.4μs.
That 0.4μs matches the low time for a BIT-1 of the WS2812B NeoPixel controller.
So we just need to generate the 0.8μs high time, in order to send BIT-1 to NeoPixel and light it up.
One way to get a longer time pulse is to add another RC time constant τ, as Julian did. (discussed in Part I of this article)
But there is another way. That is to use the “control” pin of 555 to “modulate” the…
