measuring frequency
measuring frequency
(OP)
Hi! Do any of you know of any methods of measuring frequency besides using a digital counter? r there any ways of improving the quality of the measurement like using a multiplying pll to increase accuracy? Thanks...





RE: measuring frequency
RE: measuring frequency
RE: measuring frequency
thanks for the reply
RE: measuring frequency
A Fluke 87 is rated up to 200 kHz.
Might be just the excuse you need to buy a new DMM.
RE: measuring frequency
RE: measuring frequency
an about 1-2 sec. pulse. Measure its lenght with the
microcomputer timer, then calculate.
<nbucska@pcperipherals.com>
RE: measuring frequency
RE: measuring frequency
RE: measuring frequency
What could be simpler or more accurate?
RE: measuring frequency
RE: measuring frequency
Good luck
RE: measuring frequency
RE: measuring frequency
RE: measuring frequency
Check the <www.technicalwork.com> for microcomputers
<nbucska@pcperipherals.com>
RE: measuring frequency
RE: measuring frequency
maybe with all the newer tech, people don't remember how to use them.
RE: measuring frequency
A scope is the obvious choice for one time measurements provided you have one that will measure the frequency. If it does not have this function then how do you propose to measure the frequency in real time using an oscilloscope without other interfaces(communications, logging capability,etc.)? And if these other interfaces were available to the scope then it would likely measure the frequency in real time.
A meter with frequency capability is a cheaper solution except you can not do anything with the information except display it. What if he wants to take an action when the freq falls out of a certain range? A micro has limitless possibilities in this area. Not only can you measure and display the information but you can take an action; energize a relay or SS device, communicate with a PC, call a telephone number, etc. Sure add-ons to meters allow communication, logging, etc, but you can not take an action without interfacing to some other device. Bottom line-buzzly knows what he needs to accomplish and if a scope is not an option then so be it.
Crowbar,
I am afraid with the newer technology, knowing how to use a scope is more important now than it ever has been.
RE: measuring frequency
I don't discourage anybody from playing around, but let's be realistic here. Micro projects are notorously laborious and very sensitive to any changes (hardware OR software). If you want to measure something, don't fool yourself and think that you will design something in your spare time that will outperform a dedicated piece of equipment that has proven time and again it's usefullness, and accuracy.
However, if you really want to do this with a micro, go with a high-sample rate, high-bit count A-D, and get yourself a fast micro. You will want to run a fast micro so you have enough time to sample your data and actually process it real time. Otherwise, you will be forced into acquiring and post-processing or you will need a DSP for real time processing capabilities. (Wait a second, now is sounds like your building a o'scope).
Hopefully, you have determined a good method for connecting your micro project to your signal. You will DEFINITELY need a scope to verify that your circuit doesn't load down your signal (resistively AND capacitively). I would suggest a very high impeadance (~10Meg) dummy load, but the C might be tricky. You will obviously want to keep it very low (in pF range) otherwise you can be modifying your signal and thus the resulting measurement will be useless. If you are connecting to a clock output from another IC, you must be very sure that you don't load it down, otherwise you could cause your whole system to become unstable or crash.
Also, what programming languages do you know, C, Assembly, etc.? Are you comfortable enough to learn one on your own? Are you comfortable trying to debug your code? What tools do you have available to debug (scope, logic analyzer, software, etc.)?
Why would you want to only check to see if the frequency has changed? Don't you want to know what the signal looks like? Just because your micro tells you that the signal is operating at 50KHz, don't you need to know if it is a 50KHz sinwave, squarewave or worse, something in between? Isn't the duty cycly also important? Are you looking for glitches? If so, how short?
Once again, I applaud your desire to try something new, but I don't think that this project is as easy as it seems. However, it would definetly be a very good learning experience!
Good luck and keep us posted!
RE: measuring frequency
You seem to be going to great lengths to prove that a scope is the best tool to use. Yet you don't know just what buzzly needs to measure - or why. Info that buzzly has not submitted is:
What range of frequencies? Is waveform important? Is it a one-off measurement, or for continuous monitoring? What action is to be taken with the data? Are records to be kept?
Until this is known, the best instument to use cannot be decided.
RE: measuring frequency
You seem to be going to great lengths to prove that a scope is the best tool to use. Yet you don't know just what buzzly needs to measure - or why. Info that buzzly has not submitted is:
What range of frequencies? What accuracy? Is waveform important? Is it a one-off measurement, or for continuous monitoring? What action is to be taken with the data? Are records to be kept?
Until this is known, the best instument to use cannot be decided.
RE: measuring frequency
Pebe you are right
It is a BIG mistake to solve an unknown problem !
It is a BIG mistake to solve an unknown problem !
<nbucska@pcperipherals.com>
RE: measuring frequency
You are right, I am going out of my way to prove that the scope is the best tool for the job, because the scope IS the tool for this job. Not only will it give the most accurate results, it offers more functionality than is currently required. My recommendation is based on what the user needs today, and what he is likely to need tomorrow (based on his VERY limited information). Frequency by itself does not give you the whole story! 2 signals can have the exact same frequency, but that doesn't mean that both signals are the same. Try putting a sawtooth waveform into a clock input that is designed for square waves.
RE: measuring frequency
The best way to improve the accuracy is :
1.) Use more accurate reference frequency
2.) and more time to measure.
Digital counter's accuracy is unlimited, given
ideal reference and infinite time.
<nbucska@pcperipherals.com>
RE: measuring frequency
there are so many chips that measure the frequency directly
and you don't need to setup a microprocessor based circuit to measure frequency
here i introduce the most widely use frequency to voltage converter of the world!!!
it's also very low cost
national semiconductor's LM2907/LM2917 Frequency to Voltage Converter
General Description:
The LM2907, LM2917 series are monolithic frequency to
voltage converters with a high gain op amp/comparator designed
to operate a relay, lamp, or other load when the input
frequency reaches or exceeds a selected rate. The tachometer
uses a charge pump technique and offers frequency
doubling for low ripple, full input protection in two versions
(LM2907-8, LM2917-8) and its output swings to ground for a
zero frequency input.
Advantages:
* Output swings to ground for zero frequency input
* Easy to use; VOUT = fIN * VCC * R1 * C1
* Only one RC network provides frequency doubling
* Zener regulator on chip allows accurate and stable frequency
Applications:
* Over/under speed sensing
* Frequency to voltage conversion (tachometer)
* Speedometers
* Breaker point dwell meters
* Hand-held tachometer
* Speed governors
* Cruise control
* Automotive door lock control
* Clutch control
* Horn control
* Touch or sound switches
and many other user defiend applications!!!!
like your application
if you need more go to www.national.com and download it's data sheet.
RE: measuring frequency
If someone wants to know how to crack a nut, it is better to ask how big the nut is before offering him a sledge hammer.
RE: measuring frequency
RE: measuring frequency
RE: measuring frequency
BTW, could someone PLEASE explain why the oscilloscope is so repulsive? I don't think that anyone has offered a good explanation of why one of the most commonly used pieces of lab equipment is no longer acceptable to measure frequency. Also, why do we think that we would NEVER actually want to look at the waveform? Call me old-fashioned, but I kinda like to know what I'm dealing with.
RE: measuring frequency
RE: measuring frequency
RE: measuring frequency
Before I stoop to such a low level, this is my last post unless something meaningful is posted.
RE: measuring frequency
However, let's examine why my suggestion make sense. 1) The user asked a vague question that suggests that they either don't know what they need, or they are looking for a unique solution. When the micro solution was suggested, he/she admitted that they have never used a micro before. Therefore, this person has probably never debugged a micro project before.
2) Let's go on the assumption that this person doesn't know what they need and after some troubleshooting / debugging, they decide that they need additional functionality. If it is easily added in software, then it doesn't cost anything except time. Otherwise, it would require more hardware and additional software (troubleshooting and debugging).
3) I have tried to be impartial and simply suggest a solution that will work for MOST situations. Then when I tried to get someone to explain to me why the micro solution is better, people got defensive and would not consider other options. I agree that in certain circumstances, the scope is the worst tool for the job. However, you must admit, that for most circumstances, it is the best. I took an educated guess at what the poster needed, and suggested a solution based on some assumptions. If ANYONE would have given an answer other than, "a scope is not the only solution", I think this thread would have gone in a different direction.
Finally, I know that you, BUZZP, are probably pretty upset with this discussion, but I am very happy that there are people out there that are passionate about helping others! People like you are what makes this site so great, and I hope that our disagreements don't disuade you from helping others with your knowledge. I have read many of your posts and have always been impressed with your knowledge and understanding of technical matters.
RE: measuring frequency
I've had this thread marked and have been watching it faithfully. I can agree with the points all have you have made. If the Genie in the bottle were to grant me ONE wish it would be to walk into HP (or your favourite manufacturer of the best equipment) with a blank cheque.
On the other hand I'm quite competent to design and build equipment as good as or better than any of them could offer. However, time is money, and that approach wouldn't be economically sound.
What I ask you to take note of, is regardless of your approach, that you remember you're dealing with a neophyte here; someone who hasn't yet learned to convert a period measurement to a frequency measurement. What good is either top-of-the-line or sophisticated homebuilt equipment to him? This thread is great for those of us in a position to argue the virtues of one approach over the other, but keep it simple.
RE: measuring frequency
RE: measuring frequency
I just rummaged through this thread for the first time and it is highly interesting.
I am far from being initiated into electronics. Hence, please excuse me if I am being irrelevent. But I can't help but suggest the following:
Convert the alternaing signal to a pulse using possibly a diode and associated circuitry which I suppose should not be complicated. Input this to an electronic switch compatible with Personal Computer (after moderating the pulse voltage/current values and/or matching the output and input impedences respectively of the circuit giving out pulse to that of the electronic switch). The switch then sends zeros and ones to the PC. And a suitable free software can count the pulses and the associated time and calculate the frequency.
This way, you can plot the graph, monitor continuously and format the display to your liking.
And foremost, a PC is the most likely available instrument anywhere.
Hope I am not too much off the mark.
With utmost humility.
Happy NEW YEAR to all.
sunny123
RE: measuring frequency
http://www.accesio.com/go.cgi?p=../analog_input/a1216e.html
TTFN