Saturday, March 5, 2011

Analog-to-"Digital Storage" Oscilloscope

Starting with a plastic jar, and some odd-and-ends, I was able to add "digital storage" capability to my analog oscilloscope. See sample waveform.

In case you had not guessed already, this is a pretty simple hack that enables me to consistently take good quality digital photos of my analog scope display.  By mounting a digital camera to the oscilloscope so that a low-light timed exposure can be taken, I do not have to use the camera flash and.



Materials:
  • (1) analog oscilloscope (in my case Tektronics 2213A)
  • (1) large plastic jar with a bottom large enough to span the scope display's width and height to enclose each of the bezel's edges.
  • (1) digital camera (small, lightweight with timer)
  • Velcro(TM) or adhesive hook strips and/or glue (hot glue gun)
Tools:
  • Sharp knife and/or Dremel tool
  • Glue gun (optional)
  • Tin snips / metal shears (optional)

Step 1: Go Nuts!

Empty a large plastic jar. Be sure to have a lid that is large enough to cut a hole for your camera lens and mount the digital camera to. You also need the bottom of the jar to span the outer part of the display bezel. For my case, the Kirkland Fancy Cashews jar worked great.

Testing Bottom of Plastic Jar for Size and Fit

Step 2: Mark & Rough Cut Bottom of Jar

Measure the scope display and mark an outline on the bottom of the plastic jar. You can trim back the parts that will form the sides more than the top and bottom parts (relative to scope display). I recommend using a "paper-rub" to get the scope display dimensions perfect and be sure to mark for "under cutting" giving plenty of room to cut more as you fine-tune the fit.

Paper rub of display outline.


Marked for rough cut.


Finished rough cut.

Step 3: Fit and Fine Cut Bottom of Jar

Since the jar is not perfectly square, start by cutting out the corner notches. This will make the fine cutting a little easier. To get the right fit takes some patience; Cut a little, measure and repeat until it fits "square" with the display. I recommend using tin snips or whatever else gives you a safe and controlled cut. At this point, you may also fold the top edge down to hook into the bezel groove. After the fold, more trimming may be required to set the other 3 edges (not-folded!) to be flush with the 90-degree-folded edge.

Corner notch cut. (with folded top edge.)


Corner notch cuts when connected to scope. (Note: Top fold fits into bezel groove.)



Step 4: Mark & Cut Jar Lid

Next, you need to determine the "12-o'clock" position of the lid and mark it.  You can see the 12-o'clock position marked in the hole saw picture (below).  This mark will be the 'up' position when the jar lid is attached to the jar while mounted on the scope.

Now, cut a hole in the lid that is at least the diameter of the camera lens. You may also consider cutting it large enough, or cut additional holes, to include the flash and any auto-focus assist light. I used a 1.5 inch hole saw on my drill press for a nice clean cut in the center of the lid.

Clean cut with hole saw and drill press.



Step 5: Attach Mounting Hardware


To keep things simple, I used adhesive "hooks" product from 3M to attach the camera to the lid. The position of the adhesive will depend on where the "up" marking is and the camera.  Below, are some pictures of the mounting hardware and assembly.



Rev 1.0: Finished

Well.  That was it.  But, I soon found several shortcomings:
  • The hooks adhesive did not support the torque of the camera weight very well.
  • I could not rotate the lid to adjust for the effect of the torque.
  • The adhesive did not stick very well to the plastic lid.
  • There is a lot of glare reflected from the display unless I turn off all lights behind the camera.
Here are some more pics taken with this setup where I found I liked the pics best when the camera was in Black & White mode.




Rev 1.1: Summary

So I made some minor changes to improve the performance of this camera mount:
  • Fashioned some "L" brackets from some scrap metal I had in my shop.
  • Created a cardboard platform to set the camera on.
  • Set the camera platform so that it was plumb at 1-o'clock instead of 12-o'clock.  This makes it possible to rotate the camera within 10 to 15 degrees of plumb vertical.
  • Painted the inside of the lid side of the jar matte black to reduce glare from outside light sources
  • These improvements are illustrated in the following pics.


Final Thoughts

Well, I basically got what I wanted; a way to take crisp clear pictures of my oscilloscope display.  I still need to figure out how to illuminate the grid from within the jar.  I may add some LEDs.  But, I may have to deal with glare again...

This project got me thinking about some other hack ideas:
  1. I've found that single-shot capture is may be necessary for some IR hacks. (Depends on the IR remote used.  So, it got me thinking about if/how I could trigger the digital camera "shutter" to synchronize off of the scope trigger.  Ideally, I could implement a "single-shot" capture like a real DSO.
  2. An even more ambitious idea: Hack the internal display control voltages and use an ADC to capture the waveform.
  3. Add support to make the scope a multi-channel (>2 chan) digital logic analyzer/display.  (Hack-a-Day recently had a post on this.  (See: http://hackaday.com/2010/02/11/use-an-analog-oscilloscope-to-display-digital-logic/)).
Well, those will have to wait.  I have other plans for my lil' o'scope before I start with more scope-related hacks.

5 comments:

  1. 1) Getting an idea that something could be better
    2) Thinking and design it from scratch
    3) Make it

    Simple "hack" but a truly genious way of life. Keep the life hacks coming! :-)

    ReplyDelete
  2. Hi. Nice hack. I've been thinking, a good way to reduce glare is to put a polarizing filter in front of the lens.
    P.S. Somehow this hack made me think about Williams tubes :)

    ReplyDelete
  3. OMG!!! time/cost = buy a digital storage osciloscope....

    ReplyDelete
  4. Yes, This is really nice. Now Digital Storage Oscilloscope is starting to become better and better and more portable...plus the design are now becoming more modern. www.scientechworld.com

    ReplyDelete
  5. Ingenious! You could add a triggering circuit to control the camera...

    ReplyDelete