frequency counter & 555 questions

[sagar474]

A 555 operating as a monostable multivibrator has a C1 = 0.01 F. Determine R1 for a pulse width of 2 ms.

A. 200 k
B. 182 k
C. 91 k
D. 182

A frequency counter ________ a signal.

A. measures
B. displays
C. measures and displays
D. measures, displays, and generates

 

[ADITYAVARDHAN]

A frequency counter measures and displays
a signal.

---------- Post added at 03:03 ---------- Previous post was at 02:36 ----------

A 555 operating as a monostable multivibrator has a C1 = 0.01 F. Determine R1 for a pulse width of 2 ms.
Answer:182
Formula pulsewidth=1.1*R*C
I think it is correct.please correct me if I am wrong

 

[jpanhalt]

A frequency counter measures and displays
a signal.

I thnk in the context of the original question, "frequency counter ________ a signal," "measures and displays" is incorrect. A frequency counter does not display the signal (in my experience). It does display the result of the measurement, but that is not what the sentence means, if the substitution is made.

That leaves only answer, "A," as the most likely answer.

John

 

[mister_rf]

Yes for the 555 circuit series we have t=1.1RC, but we need to use R in ohms Ω, C in Farads in order to obtain seconds.
C=0.01F
t=2ms=0.002s
R= 0.002/(1.1)(0.01)= 0.18(18)Ω

A, B, C, D no valid answers...

 

[betwixt]

Hmmm.... I suspect the question is quoted wrongly as the 555 would never work with those values. Sagar474, check the capacitor is not supposed to be 0.01uF not 0.01F as you wrote. If I'm right and it should be microfarads, the answer would be 182K.

A frequency counter can only measure frequency. It could be part of a larger electronic circuit in which case it's result would be read and used by other circuits or, it could be a stand alone test instrument in which case it still measures frequency but would need a way to display it to the user.

Brian.

 

[FvM]

And does a frequency counter measure a signal? It measures only a parameter of the signal. So answer A at least isn't very exact. On the other hand, an interviewer, who considers answer A correct would most likely prefer answer C.