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Old 25th April 2008, 09:27 AM   #21
h_a is offline h_a  Europe
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Ok, so I misunderstood.

Of course interesting, however I think that most people here don't have the object to be analyzed, that is a distortion analyzer

Have fun, Hannes
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Old 25th April 2008, 09:41 AM   #22
Nordic is offline Nordic  South Africa
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http://www.serasidis.gr/circuits/AVR...cilloscope.htm

Click the image to open in full size. would be neat to have a standalone unit... not needing a scope.
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Old 25th April 2008, 11:55 AM   #23
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@Nordic
this reminds me in someway to the Gameboy Digital Sampling Oscilloscope

@G.Kleinschmidt
nice project i'll keep on watching ...
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Old 25th April 2008, 01:08 PM   #24
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Quote:
Originally posted by G.Kleinschmidt

After that I will work on converting the <10Hz resolution ~90dB dynamic range analogue end and hybrid PLL working at 20-200,000Hz.

Cheers,
Glen
Think "Crystal filters" --- which is how HP did it.
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Old 27th April 2008, 07:48 AM   #25
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Quote:
Originally posted by jackinnj


Think "Crystal filters" --- which is how HP did it.

Yes, I used crystal filters in my previous design.

For those that are interested, the design will be presented in full here:

http://users.picknowl.com.au/~glenk/SA200K.HTM

Don't expect much for a while though, this is going to take me a while.............
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Old 28th April 2008, 12:38 AM   #26
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I have done a bit with Fourier transforms to convert the signal to the frequency doman.

It just needs a fast ADC and a good processor to do the maths.
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Old 28th April 2008, 05:52 AM   #27
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OK, an update.

I have finished revising the design of the digital sampling board and am 70% through drawing the schematic in Protel.

I have also decided to take a different approach with the design, after realising that this section of the Analyser would be a very useful piece of test equipment on its own, essentially being a self-contained low frequency digital storage adaptor of an analogue oscilloscope.

Anyone who has used an analogue oscilloscope to look at low frequency waveforms would know what a waste of time it is, especially when the horizontal sweep rate is so slow that the persistence of the display makes the wriggling dot look like a little comet flying across the screen.

I have named this self-contained DSO adaptor the DSOMK1, and have added it to the contents page of my website (currently under development) under Test Equipment:

http://users.picknowl.com.au/~glenk/HOME.HTM

The DSOMK1 will allow nearly any analogue oscilloscope to display low frequency signals, recorded at horizontal sweep rates from 0.1 seconds per division to as low as 50 seconds per division.

The nearly finished schematic of the DSOMK1 is attached below. All I still have to add is the PIC16F876 microcontroller and control interface on the left of the page and a buffer opamp for the ADC input.

The operation of the unit is very simple. There are two 1k 8 bit static memory chips. At any one time, one will be put in read mode for generating the display on the oscilloscope CRT while the other is in write mode for recording the input signal at the selected sweep rate of 0.1s to 50s per division.

While recording, the display memory is continuously clocked completely through its 1024 bytes at a rate of 25 times per second, in synchronisation with the 10 bit ring counter and R/2R DAC at the bottom of the schematic that generates the 25Hz saw tooth horizontal sweep waveform, fed into the X amplifier input of the oscilloscope.
The output of the memory chip being read is decoded by an 8 bit R/2R ladder DAC and sent to the oscilloscope vertical input.

This provides a flicker fee, static display of the last recorded long-duration sweep on the oscilloscope display until the microcontroller has completed recording with the other memory chip. Then the other memory chip with the fresh recording is switched into display mode by the microcontroller, while the next sweep is then recorded into the memory previously used for display. This process repeats continuously.

The horizontal sawtooth sweep output for the oscilloscope X input is +/-2.5V peak while the Y (vertical) output for the oscilloscope Y input is +/- 2V peak, with -10V 1mS pulses during the horizontal retrace interval to ensure that the trace is deflected off screen to prevent visible retrace during this period.

These voltages ensure that the display fro the DSOMK1 will fill the typical 10cm (Horizontal) by 8cm (vertical) display of the analogue oscilloscope with the variable positions controls centred and both the horizontal and vertical deflection amplifiers set to 0.5V per cm/division.

I hope I've explained that clearly

Anyway, the design uses cheap garden variety parts, the semiconductor complement being:

One PIC16F876 (The master controller)
One 20MHz 8 pin oscillator module (heartbeat for the PIC)
Two CY62256 SRAM (the memory, only addressed for 1kbyte)
Three 74HC4040 (for RST synchronised address counters)
Two 74HC573 and two 74HC574 (for MUX'ing the ADC and the DAC to the alternate memory chips)
One ADC0804 (8 bit ADC)
One LM336-2V5 (Voltage reference for ADC and voltage level shifting of X/Y output signals)
One TL081 (input buffer for ADC)
One TL074 (X/Y output)

Cheers,
Glen
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Old 28th April 2008, 04:04 PM   #28
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All done.

Now onto the hybrid DDS/VCO PLL for the swept local oscillator........
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Old 29th April 2008, 12:38 AM   #29
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Mr Kleinschmidt,

Could you , somehow, add pictures with higher resolution ? The pictures you have attached do not have high enough resolution to see the details i.e. symbols, values, letters.

thanks in advance
Dimitar
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Old 29th April 2008, 03:21 AM   #30
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Quote:
Originally posted by Dimitar13
Mr Kleinschmidt,

Could you , somehow, add pictures with higher resolution ? The pictures you have attached do not have high enough resolution to see the details i.e. symbols, values, letters.

thanks in advance
Dimitar

Hi Dimitar

Those pics are just for a bit of a progress report. Detailed schematics and all details (uC code, etc) will go on my website once the design is built and tested and debugged.

This may take a while though, but I am eager to get the complete design up an running to conduct some detailed measurements (paired with a THD analyser) of a series of power amps I'm building, so it does atleast have a reasonably high priority

Cheers,
Glen
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