7 replies to this topic

[betoe]

Hi guys, i want to make an AFX osciloscope!!! watch this link, it have some help for put a signal on a calculator, but i dont know how to determinate the frequency (my friend and me know how to make 8086/c programs, and how to put signal values in the calculator, and i think that we can graph them).
FX data logger

I have another idea: introduce the signal to a ADC (8 bits or more), then to a 8051CPU (it have serial port communication) for send the data to the calculater. Then all the rest is pure software. A teacher told me this for the frequency: obtain the TDF (discrete fourier) of the signal. What the F*** how to do that... Hope i can do this project.

[2072]

Casio has already build such a thing, I don't remember the name, but you can find it on their site.

[Andy.Davies]

and there is that data sampler that i showed you a while back, that would only need to be modified

[betoe]

Oh yes i didnt remember that. I would like to be more like an osciloscope, that bring frequency etc... The bad thing, as i think, is that the higher frequency for that AFX osciloscope will be:

For send a byte we need 10 bits (8 of data, 2 of stop), and the max speed of the AFX serial port is 115,000bits/seg. I think that the max frequency that this oscilloscope will be around 6KHz , its too small.

[Andy.Davies]

you could always buffer the input on the hardware, then send it in bursts to the AFX, therefore making i t lag but having a higher frequency

[Mohamed]

Casio has already build such a thing, I don't remember the name, but you can find it on their site.

What is that? Do you mean tha EA-100 & EA-200?

and there is that data sampler that i showed you a while back, that would only need to be modified

Again, where is that? I'd love to see such things.

betoe:
WOW, finally you get an interesting project.
It seems nice, and I looked at the page you linked, very interesting.
As for the frequency thing, I don't have a clue how you're going to get doing the DFT (or TDF if you're studying in French, they always turn sentences upside down ) using the AFX or the ASM language!!!

I might think you'd want to get the zero crossings for the signal, measure the number of clock cycles it takes for a period or half a period (every ASM command takes a certain number of clock cycles, you get that from the micro controller's data sheet), then by knowing the frequency of the crystal, you get to know approximately the frequenct you want.
But that souns like a dumb idea (I used it once in an opposite way to generate a signal with a certain frequency), there must be a smarter way like that DFT, I'll just look on the net for how these digital frequency measuring devices are made.

Please keep us updated and good luck.

[Andy.Davies]

here is the link to the data logger: http://www.riccibitti.com/casio.htm

the only problem is the ADC chip costs ?20:00

[betoe]

For the zero crossings there is no problem. One doubt, what CPU is fastest, the NECV30 (of the AFX) or the 8051CPU at 12MHz? Damn i told this project to my teacher and he dont like this idea , he told me that i must do other project. Anyway i'm interested in it.