PC Based oscilloscope with at lest 1MHz

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anandpv2009

Joined: 11 Aug 2009
Posts: 63
Helped: 4
Location: India

05 Nov 2009 14:12 PC Based oscilloscope

I need a PC based oscilloscope circuit.It should have a bandwidth at least 1mhz.
My idea is

VOLTAGE TO FREQ.CONVERTER IC ------>PIC18F2550/4550----->PC----->SOFTWARE

I am willing to write software for oscilloscope in PC but I have no enough knowledge to design the circuit.I am planning to use HID communication to interface PIC with PC

Any idea.... Please post your idea because i need a scope but i don't like to spend more money to buy one...

Thanks.....

betwixt

Joined: 04 Jul 2009
Posts: 383
Helped: 62
Location: Wales, UK

05 Nov 2009 14:50 Re: PC Based oscilloscope

That *might* work but I doubt you would see any advantage over simply measuring the voltage with the on-board ADC.

The problem:
To measure DC up to 1MHz your V to F converter will have to run at a much higher frequency and have a linear conversion factor. The PIC can measure frequencies but not if they are very high, the resolution will not be good. Also consider that trying to accurately and continuously measure frequency may be difficult while also handling USB transfers.

Brian.

anandpv2009

Joined: 11 Aug 2009
Posts: 63
Helped: 4
Location: India

05 Nov 2009 16:18 Re: PC Based oscilloscope

I think it is possible if V to F conversion is possible.
Any one can suggest a circuit that converts Voltage to Freq. (1mhz bandwidth)

Thanks[/code]

nandhu015

Joined: 11 Feb 2006
Posts: 640
Helped: 46
Location: Tamilnadu, India

06 Nov 2009 15:12 PC Based oscilloscope

hai anand

Have you searched the net?

There are some nice completed projects on the net

this is one of them
http://www.semifluid.com/?p=24

search the net you will find more

Nandhu

Jack// ani

Joined: 02 Dec 2004
Posts: 488
Helped: 25

06 Nov 2009 19:21 Re: PC Based oscilloscope

nandhu015 wrote:

this is one of them
http://www.semifluid.com/?p=24

Nice one, very resourceful link.

Thanks for sharing with us.

dian

Joined: 16 Apr 2006
Posts: 41
Helped: 7
Location: Indonesia

07 Nov 2009 14:04 PC Based oscilloscope

i agree with betwixt why dont you direct convert the volatge with ADC? Every conversion step will reduce the accuracy, would you explain why you need to convert the V to F first?

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anandpv2009

Joined: 11 Aug 2009
Posts: 63
Helped: 4
Location: India

07 Nov 2009 16:29 Re: PC Based oscilloscope

Amplitude of voltage to the PIC A/D input is limited that is why I suggested V to F ICs. I recently saw a EFY magazine (not new) with constructional details + schem. of microcontroller based oscilloscope.

betwixt

Joined: 04 Jul 2009
Posts: 383
Helped: 62
Location: Wales, UK

07 Nov 2009 19:52 Re: PC Based oscilloscope

Measuring in the voltage domain is quite easy although achieving 1MHz bandwidth without using special hardware could be a problem. The internal ADC in a PIC isn't fast enough to sample at 2MHz (the absolute minimum rate to see 1MHz signals).

If you convert to frequency, the measurement becomes far more difficult. To be able to measure a frequency which is modulated at 1MHz, it has to be at least (Nyquist limit) 2MHz at it's lowest and a PIC will struggle to measure such short cycles accurately. If you increase the frequency to improve resolution, you decrease the ability to measure it accurately. Even if you could measure it, at such high frequency deviation it would be very difficult to keep the frequency increase linear to the voltage.

You might be able to sample fast enough if you use two or more PICs with the ADC triggering alternating between them but keeping them in sync would be difficult.

Brian.