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Two channels!

Way back in my childhood (when dinosaurs ruled the Earth) our black and white television provided two channels for our viewing pleasure. One channel was pure drivel and the other one was worse, so suffice it to say that I didn't watch a great deal of television!

These days I would love to go back to just two channels for my viewing, as the dazzling array of choice available to our jaded palates now can make us feel (and act) like the proverbial donkey starving between bales of hay.

Recently at the lab bench I found myself lamenting that I didn't have two channels when I wanted to monitor a circuit at two different points. I could see one thing happening at one point, and another at another - but how they interacted was a matter of ignorant conjecture!

For a while as well I have been hinting at my work (a high school) that the clapped out oscilloscopes gathering dust on their shelves would be much better employed as my plaything in the dungeon I call my garage/lab. Very Mary Shelley I know.

So you could have knocked me down with a feather when, after months of "tactful" campaigning - a dusty Analog Cathode Ray Oscilloscope (CRO) that surely Noah used to trim the Ark was bequeathed to the weirdo from the Math dept who just didn't seem to get the hint.

And so it came to pass that a knock off version (from Hung Chang) of a Protek 6502 ended up on my lab bench. My beating heart!

Two questions needed to be answered in my first session with this relic:

1. What would happen when I gave it power and pushed the button?

2. Assuming it did function, would I be able to get it to do anything meaningful given I did not read the manual, and last played with an analog oscilloscope back in 1981 at university!?

The Protek looks like this:

What do you think will happen when the cheap knock off CRO is powered on for the first time in a couple of decades?

To test the device I used a classic Op Amp relaxation oscillator with a classic Op Amp at it's heart, the TL072 (touted as being just peachy for making audio amplifiers). I have used this circuit before in a video and blog about the LM358.

I wanted to see the Op Amp circuit produce a square wave as the capacitor rose and fell in voltage. To do this I need to monitor the circuit at two points using two channels and my trusty (!?) DSO138 was good for only one channel (and somewhat unreliably at that).

Here's the video result - enjoy!