Pc based oscilloscope

[jonw0224]

sram diy oscilloscope

Unfortunately, the ADC 0804 appears to sample at around 10 kHz maximum (uses successive approximation). Your sound card does better and there are plenty of free programs out there which turn the sound card into a slow oscilloscope.

You need to:

(1) get a faster ADC (the one i use has an internal track and hold and samples at 1 Mhz)

(2) control it with something faster than the parallel port. I didn't use the port because the speed varies from PC to PC and I didn't want to calibrate the time scale with some standard wave. I am using a microcontroller. Most of the time that's not fast enough so most people (like bitscope) use a CPLD.

(3) build a memory buffer to sample (I'm using ram internal to the microcontroller), then communicate with the computer at a slower speed.

I don't understand that adc0804 was expensive. I looked on digikey and it was $3.00 to $10.00. Digikey also has the max118 for $9.50. You can go even faster like the AD9280 which samples at 30 MHz for $5.00.

 

[aibelectronics]

fast adc pc oscilloscope

Unfortunately, the ADC 0804 appears to sample at around 10 kHz maximum (uses successive approximation).

hmm...but sampling at 10khz surely would give the circuit the capability of measuring much more than 1khz? I do wonder what could be the main reason limiting it to 1khz? The parallel port? - that'll change the oscilloscope's code entirely. By callibrating the time scale by some standard wave I suppose they mean putting the time-axis to last the duration in which that standard wave would complete its cycle?:|

 

[jonw0224]

adc0820 oscil

hmm...but sampling at 10khz surely would give the circuit the capability of measuring much more than 1khz? I do wonder what could be the main reason limiting it to 1khz? The parallel port? - that'll change the oscilloscope's code entirely. By callibrating the time scale by some standard wave I suppose they mean putting the time-axis to last the duration in which that standard wave would complete its cycle?

Yes, nyquist says you can measure a sine wave of just under 5 kHz by sampling at 10 kHz. However, most people say you need 10 samples/cycle to get a good idea of the waveform shape (hence 1 kHz). At 10 samples/cycle you get information about he fundamental and the first four harmonics.

The parallel port can run much faster than the ADC. In fact, if you look at the code, it toggles many pins to read one sample. The code waits for the INTR pin to go low on the ADC signaling a final conversion. So, I was mistaken, the timing is actually determined by the RC oscillator on the ADC. It's sampling at about 10 kHz. Comparing to a standard wave will allow you to calibrate the timescale for the tolerances of the RC oscillator (but what about drift, do you calibrate before each use?).

I want to build the scope in the link below but couldn't find this fast ADC0820, so cpuld anyone give me another part that is quite similar to this.???

If you look at the ADC I am using (maxim ic MAX118), the pinout interface is very similar. It may work and it is atleast worth comparing the datasheets.

 

[aibelectronics]

simple oscilloscope lpt diy

Yes, nyquist says you can measure a sine wave of just under 5 kHz by sampling at 10 kHz. However, most people say you need 10 samples/cycle to get a good idea of the waveform shape (hence 1 kHz).

thanks, helped me once again. you said the adc 0804 samples at 10khz? but it seems they are using an external clock running at ~640khz?
10 samples/cycle implies 1khz? How is that?
I think for my purpose a 10khz maximum is modest as i'm only doing it for school project, I believe an oscilloscope capable of only 5v (pk-to-pk) and 1khz is too limited...
Eagerly awaiting your reply.

 

[elexhobby]

can i put an oscilloscope on my computer

jonw0224

Since u r storing & then displaying, the oscilloscope won't be a real time one.
However with a parallel port, u can build a real-time oscilloscope.
Have any ideas for a realtime oscilloscope but faster than the parallel port

 

[aibelectronics]

pc based oscilloscope using rs232 circuit diagram

I hear there are free source codes for sound card oscilloscope, much faster...

 

[jonw0224]

microcontroller adc oscilloscope

First, I wanted to appogize for a mistake. The prototype on my webpage has a maximum sample rate of 200 kHz not 250 kHz. Apparently, I can't divide 1 MHz by 5. I didn't want to mislead anyone.

you said the adc 0804 samples at 10khz? but it seems they are using an external clock running at ~640khz?
10 samples/cycle implies 1khz? How is that?

Apparently the ADC requires 64 clock cycles to do a conversion. The datasheet actually says 66.
Ok, 1000 cycles/second = 10000 sample/second / 10 samples/cycle

Since u r storing & then displaying, the oscilloscope won't be a real time one.
However with a parallel port, u can build a real-time oscilloscope.
Have any ideas for a realtime oscilloscope but faster than the parallel port

Yeah, it's not real-time. But why would you need real-time? If it updates once every 300 ms or once every 100 ms, that's about as fast as my brain works. I have no idea how to make a digital oscilloscope that doesn't have some display latency.

This brings up a point though, in most modes I am sampling 64 times on channel 1 then 64 times on channel 2 (sychronized by the trigger). I have a slower mode that samples on channel 1 and then on channel 2 a total of 32 times. This was to address times when I need to sample concurrently, but the operation is slower. One of my goals was to make the "true XY" sample mode much faster in the new version.

 

[jonw0224]

parallel port oscilloscope using max118

I noticed that the file I put up at the link wouldn't work on another computer. Turns out, I was using LPT2, which many computers don't have. The program was crashing right away....

It's updated to use LPT1 as I intended. Sorry if this messed anyone up.

 

[seadolphine2000]

diy fast oscilloscope

Here you are the oscilloscope based on the ADC0820.

www.geocities.com/lptscope/index.html

 

[thesandman]

scope para pc con adc0820

I've seen a variable 2hz - 260Mhz sample done using the MAX1448 ADC, fast RAM and a PIC. Trying a similar application, but only need to sample at 1M.

 

[wakaka]

guterman osciloscope

Hi guys, I've browse thru the forum, but still cant find any clear source regarding a PC oscilloscope. But I've found this thru google :
h**p://www.semifluid.com/

Although its not a PC osc, but it looks nice, plz comment guys.
And plz recommend a better scope, either PC osc or a portable osc which can be fully built from scratch.

THankx