Yep, I understand thatHello,
During the charge state the discharge transistor is not having any current.
The voltage of the capacitor is the input to BOTH comparators.
The comparators have different comparison levels.
The lower one (trigger) is at 1/3 VCC, the upper one (threshold) is at 2/3 VCC.
In the applet you could see the trigger starts the "fill" cycle and
the threshold starts the "release" cycle.
Greetings,
Bertus
Ok. As it's flowing into the capacitor, how does the threshold pin not read that Voltage?"All" the current from the resistors (Ra+Rb) will flow into the capacitor during the "fill" cycle.
Ok, good. Thats what I was trying to get at.Hello,
The threshold only sees the voltage of the capacitor.
The capacitor delays the voltage coming from the 9 Volts through the resistors Ra+Rb.
Greetings,
Bertus
RightHello,
The resistance of R(1)a+R(2)b together with the capacitor give the delays.
You can calculate t1 and t2 times with the formulas below:
t1 = .693(R1+R2)C, t2 = .693 x R2 x C
T1 is the "fill" time, T2 is the "release" time.
Greetings,
Bertus
Yes I know how it works. I thought maybe it served a dual purpose.The capacitor is there to accumulate charge at a predictable and repeatable rate. It charges through R1 & R2 in series. It discharges through R2 through the switch in the 555.
Have you read about how a 555 timer IC works?
Why does 9v not go through R1/R2?R1 and R2 do not apply 9V to the capacitor. They apply a small current that slowly charges the capacitor.
You might find this link enlightening, especially post #3. http://forum.allaboutcircuits.com/showthread.php?t=12808f you have a capacitor in series with a ciruit, once the capacitor fills up, no more electricity will flow in the circuit...correct? Or is this wrong.
by Duane Benson
by Jake Hertz
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by Jake Hertz