Hi, there. I have been looking for a way of using ne555 as a 50% duty oscillator with only one resistor tuning for frequency. Your method sounds awesome, but it's still not very clear to me how to implement it. Could you please do me a favor to show me an example circuit that can do exactly what you said? Many thanks.Don't use pin7, drive the cap from pin3 which is bipolar (through one resistor), and you just need 1 cap and one resistor and it automatically makes a 50% duty oscillator.
I have not used pin7 in a while, unless I specifically need a 555 with a duty that is NOT 50%.
Formula: T = 0.7 * (R1 + (2 * R2)) * C1 (without diode)
f = 1.4 / ((R1 + (2 * R2)) * C1) (without diode)
T = 0.7 * (R1 + R2) * C1 (with diode)
f = 1.4 / ((R1 + R2) * C1) (with diode)
Symbols: T = Time period (Units: Seconds)
f = Frequency (Units: Hertz)
Mark = High time of output waveform (Units: Seconds)
Space = Low time of output waveform (Units: Seconds)
Duty Cycle = % of period T in which output is high (mark)
Data: Mode: Astable
Calculate component values
Frequency = 40 Kilohertz
Duty Cycle = 50 %
Results: Period = 25 Microseconds
Mark = 12,5 Microseconds
Space = 12,5 Microseconds
C1 = 10 Nanofarads
R1 = 1 Kilohms
R1 nearest preferred value = 1 Kilohms (E24 / 5%)
R2 = 1,786 Kilohms
R2 nearest preferred value = 1,8 Kilohms (E24 / 5%)
Diode D1 should not be fitted
50/50 is the easiest 555 circuit of all, and 40 KHz is easily within the range of both bipolar and CMOS parts.Could someone help me to generate a 40khz square pulses(Astable multivibrator) using 555timer IC,with 50% duty cycle.
And you helped keep it breathing.Another resurrected thread!
It's very strange, although I like that way, but when I tried it on one month ago and it didn't work, I did that again on yesterday, but it still can't reach to 50%/50%, I was used LM555CN and one resistor, one capacitor.Don't use pin7, drive the cap from pin3 which is bipolar (through one resistor), and you just need 1 cap and one resistor and it automatically makes a 50% duty oscillator.
I have not used pin7 in a while, unless I specifically need a 555 with a duty that is NOT 50%.
I just thought maybe you were used the CMOS type, but do they really can reach to 50%/50% or just close to.What duty cycle did you get?
It's possibly a bit off 50% due to the old TTL 555 having slightly different sink/source characteristics of the output pin 3. Some brands are worse than others.
I'm generally using CMOS 555s these days like the 7555. Faster, less power required etc.
I was used IWATSU 100Hhz O'scope to measured your circuit, it shows as below:Scott,
Have you looked at the output from the circuit I attached to post #13? My scope is not sufficient to see that much detail.