DIY digital oscilloscope

abcmann · January 21, 2009, 11:09pm

Hi, I found this today…

it looks really good for the most purposes. Better than a soundcard scope.

http://jonw0224.tripod.com/ppmscope.html

Specifications and Goal Feature List:

Feature

Current Version (v.2.01)

Goal Version

Sample Rate

Variable, single shot 1 MHz max, interlaced 151 kHz max

Variable, single shot max 1 MHz, interlaced max 417 kHz, repetitive 5 MHz

Bandwidth

500 kHz

Number of Channels

Two

Sample Depth

256 bytes per channel, 128 bytes per channel when interlaced

Sample Modes

Single shot and interlaced

Single shot, interlaced channel, and repetitive

Calibration

Voltage offset

Voltage per division and voltage offset calibration

Configuration Settings

Configuration of default and saving of settings for future use

Hardware Connection

Any parallel port

Any parallel, serial, or USB port

Coupling

AC and DC, reflected on PC

Channel gain

Gain of 1, 2, and 5, reflected on PC

Trigger

Variable level, slope, and timing

Frequency Spectrum

Yes

Waveform Reconstruction

Triangle, square, point, and sinc

XY view

Yes

Channel offset and volt per division settings

Yes

Cursors

Yes

Math functions

Only addition and subtraction of channels

Addition, subtraction, auto period, auto peak-to-peak, etc.

Waveform export

Comma delimited

Bitmap and comma delimited

I’ll build one

bye

stryd_one · January 21, 2009, 11:33pm

Nice find. Much faster than this one: http://www.midibox.org/forum/index.php/topic,8218.0.html

Shame it’s windows only

Keep us posted on your build!

abcmann · January 22, 2009, 12:49am

ill do that. i dont know if it helps, but there is the c sourcecode in the package. perhaps anybody can use it to run it under linux.

Max_Romantschuk · January 22, 2009, 5:51am

there is the c sourcecode in the package. perhaps anybody can use it to run it under linux.

Unfortunately rather unlikely unless the code was written with portability in mind… But depending on how it interfaces with the hardware Wine might be an option.

Goblinz · January 22, 2009, 9:12am

I wonder if that power supply scheme could be useful for other midibox hardware that requires +12 /-12 V ???

Do we have the numbers to get some PCB’s made up?

philetaylor · January 22, 2009, 9:28am

Do we have the numbers to get some PCB’s made up?

If a PCB manufacture is planned then i’m in!

I’m sick of my crappy Velleman handheld scope…

Phil

diablojoy · January 22, 2009, 11:08am

would also be very interested in this I do need a scope

very soon

stryd_one · January 22, 2009, 12:43pm

ill do that. i dont know if it helps, but there is the c sourcecode in the package. perhaps anybody can use it to run it under linux.

I didn’t actually check the code but the comments said that he had decided to use Window API GUI controls, so porting it may not be so simple (possible though)

Goblinz · January 22, 2009, 1:36pm

If a PCB manufacture is planned then i’m in!

I’m sick of my crappy Velleman handheld scope…

Phil

I may be getting a vocoder board fabbed at somepoint this year so think I’ll add a scope board in at the same time if there’s room so I can see it working.

People should be aware that they’ll need to use mains voltage to feed the transformer, something that I’m a little bit wary of myself.

Another point is that the listed BOm comes to $110 + the cost of the board and encloure… A second hand scope could be bought of ebay for less than this.

Jack · January 22, 2009, 2:07pm

Hi!

Before you pay over 100â‚¬, please check this for less money:

main: http://www.fpga4fun.com/Hands-on_Flashy.html

usb: http://www.fpga4fun.com/Hands-on_Flashy_USB.html

shop: http://www.knjn.com/?pg=info&src=Flashy

Best Regards

Jack

Goblinz · January 22, 2009, 3:36pm

A simple digital oscilloscope recipe

Using parts from KNJN.com, here are the basic items of our recipe.

* 1 x Pluto FPGA board, with TXDI and cable (item#1121 = $41.95)

* 1 x Flash acquisition board (item#1205 = $39.95)

* BNC connector + Male/female connectors 2x8 + Nylon standoffs/screws (item#1250 + #1275 + #1270 = $10.85)

That’s about $92.75 so far.

Not much difference.

The one mentioned earlier can be used as a function generator and as a power supply too.

MRE · January 22, 2009, 6:50pm

Look over the FPGA4FUN project again. It is essentially pre-built for one thing. (Two built modules connected together.. 5 minutes to make this thing, another 5 to download the fpga software to the board).

For another, and this is the most important part: 100MHz vs 1MHz. To be honest, that 100Mhz might actually be 50 if you want any accuracy. Nyquest says you need at least 2 or 3 samples to per cycle before you can trust it. So I would take anything over 33Mhz with a grain of salt. That is still WAY better than 1Mhz.

To spend more than $20 dollars on something in the 1-5 Mhz range is silly.

(Hand-held semi pro 5Mhz+ scope-on-the-go gear is excluded

If I were choosing between the two, Id spend the bucks, forgo the time and (marginal) troubles of building the kit, and enjoy the higher freqs of the FPGA4Fun project.

It also looks like a two channel version is possible with a bit more work (and some cash).

As well as the option for LCD output.

Finally, function generators are not that hard to get, or build when you really need one on the cheap.

I would assume everyone here would back me up on this:

When it comes to o-scopes… speed speed speed.

My handheld 5mhz unit isn’t bad. 5Mhz is good enough for most basic bench work. Its portable and not tied to a laptop. And it runs on batteries for hours. The problem with it is that, while it can sample up to 5Mhz, the screen refresh is more like 1Hz. That makes it impossible to use on all but the most stable and repetitive signals.

FPGAs are MUCH faster than a PIC for something like this. They were designed to be the digital signal taskmasters for the analog world. FPGAs eat, drink and break signal processing. Go with it, forget the PIC.

(although, if you really need that function gen, there are HUNDREDS of cheap projects for 1MHZ and lower signal generators for PIC.)

MRE · January 22, 2009, 7:37pm

It should be added that regardless of which project you choose, you will need to add significant signal conditioning and ranging circuits if you want to work with anything outside of ‘digital’ (0 to 5 volt) ranges.

The front end signal conditioner from the first project is a good start. With some mods it could be attached to the FPGA4Fun design. Id still want to add a range circuit in front of that, before connecting to the probe, in order to protect all the expensive electronic circuitry.

JMS · January 22, 2009, 8:27pm

FUNCTION GENERATOR: (and other DIY nifty projects)

http://www.nuxie1.com/guides/fungen-v2-kit.html

i started building this a while back, i even have the g-code to cnc out a board backed up somewhere. i cncd out a prototype board, drilled all the holse, soldered in the socket for the xr2206. i ordered some xr2206 samples… i never did much with the rest of the project except look at it sitting on my bench half done. i think it would be a DOPE! sound generator if attached to the midibox and a small app written, which could display the the waveforms maybe even?

here is a link to the post with a video of the code being tested on my mini mill and a pic or two…

http://ohiopctech.com/dp/?q=node/136

(sorta) OFFTOPIC: just got my mbhp_core running with an lcd today, ready message on the lcd about an hour ago! so i’ll be building some kinda function generator soon to be interfaced with this core. (and teaching myself asm in the process so i can try to code the app for it.)