How to display pulse speed of 555 in astable mode?

[jmb4370]

In using a 555 in astable mode to drive a 4017 decade counter, I would like to have a LED dsiplay of the pulse speed that is being output from the 555 (and used as the input clock to the 4017) as the speed is varied with a pot. Having just a flashing LED means I would still have to time the flashes manually. Is there another way to get the actual pulse speed to a LED segmented display, as possibly time interval between pulses, and as a pulse per minute?

 

[Reloadron]

First a little clarification. You are talking about the frequency or PRT (Pulse Repetition Time) out of the 555 which serves as a clock to the 4017. Don't use the word speed in there. Frequency and time are reciprocal values. 1/F = T and 1/T = F.

No there is no way to do what you want to do. You would need a frequency counter or a way to measure the period out of the 555. A scope would also work reasonably well but not as accurate as a counter. What you have cannot measure itself if that is what you are getting at.

Ron

 

[ericgibbs]

hi,
This link may help.
https://www.electro-tech-online.com/blogs/ericgibbs/125-simple-7555-cmos-timer-calculator-v1-2.html

Ron you son of a gun, beat me to it.!

 

[jmb4370]

Ron,

I understand what you are saying that the 555 can not measure itself, but I would like to connect the output of the 555 to the 4017, and also to a frequency counter to display the Frequency and Period of the 555 pulse (without using an oscilloscope. Does this expain it better?

 

[Reloadron]

Ron,

I understand what you are saying that the 555 can not measure itself, but I would like to connect the output of the 555 to the 4017, and also to a frequency counter to display the Frequency and Period of the 555 pulse (without using an oscilloscope. Does this expain it better?

Oh, then no problem as long as you have a frequency counter, Typical input impedance of most counters is 1 M Ohm or greater so I don't see a problem using the counter to monitor the output of your 555.

Ron

 

[Reloadron]

hi,
This link may help.
https://www.electro-tech-online.com/blogs/ericgibbs/125-simple-7555-cmos-timer-calculator-v1-2.html

Ron you son of a gun, beat me to it.!

A very, very rare ocasion.

Ron

 

[MikeMl]

Why dont you use a 10-turn pot on the 555 (or a linear pot with a nice pointer knob and scale), and then calibrate the scale/turns counter? You might need to use a sound-card scope or real o'scope to get it calibrated initially, but once calibrated, it would be resetable/repeatable with ~5% accuracy.

 

[jmb4370]

Mike,

The manual calibration is ok, but for the exercise, I wanted to turn the knob of the pot, and then see a LED readout of the Frequency of the pulse for the 555, or flip a switch and show the Period (Pulse Repetition Time). I hope this makes a better clarification.



Ron,

Do you know of any Freq Counters that can be directly used that will also display the Period?

Michael

 

[MikeMl]

I have used several freq counters over the years; all have a function switch to measure frequency or period. When the time base is 1 or 10sec, for low frequencies, you can read the frequency to only three significant figures (e.g. 12.3 Hz or 1.23 Hz), but you can read the period to ~9 significant figures (e.g. 0.08130081 sec or 0.81300813 sec, respectively).

To "build-in" a frequency readout, it would take many decade counter chips, bcd to seven-seg-decoders, seven seg readouts, a crystal oscillator, a divider counter chain (to get a 1 sec time base). In other words you are building your own frequency counter, so you might as well build one that is useful beyond this project. Another way to go is to use a PIC with a LCD display. There are many PIC-based frequency counter projects out there on the web, including Roman Black's

 

[Reloadron]

To add to what Mike covered, every frequency counter I have used going back a long time had the ability to read period. Years ago using the old HP 5245L (nixie tubes) the rule of thumb was to measure anything below 50 Hz use the period mode and DC couple the signal. Counters have come a long way with plenty of measurement features and anymore relatively good counters for hobby applications can be had fairly inexpensive.

Ron

 

[jmb4370]

Thanks for the info. I will look into a kit that I can make to measure and display the these values!