Let's Make Robots!

No need for oscilloscope, nut cracked, bright debugging ahead!


I do not have an oscilloscope, and I "always" wanted one. "So I could debug & understand & see what was going on".

Yesterday I got so frustrated that my cheap RF still was not 100% rock solid - even though I had made all sorts of initializing strings.

i got so desperate that I decided to buy a used oscilloscope. While checking out what was on sale in my area, I got the idea that perhaps I could make one myself..

That got me to look into .. "perhaps someone out there made a SW oscilloscope - how hard could that be?

And there ARE SW oscilloscopes, and they have demos!

Great, I thought. They work like this: You have minimum 2 channals / rays. Each is simply represented bya stereo channel on your soundcard's input.

.. "great" ..hmm.. yes.. well.. I realized that an oscilloscope is really not that great for my kind of debugging. They only show the present pulses, but what if your problem is little fast glimses?

Really annoyed, i got to think of an old HW music sampler on my desk.

"Heck", I thought, let's sample the outputs then..


This way I could let the robots do their buggy business, record it, and rewind, zoom, watch what's going on.. and the best of it all at the very moment: IT CRACKED THE CHEAP RF-NUT!

Now my only problem is to find time to make a real functional walkthrough on the cheap RF's, and similar stuff..


But just for now, check this blurry crap image, taken with my phone, at the heureka-moment, when the nut was cracked, and I made cheap RF rock solid with minimum of wasted bits etc:


The interesting part is the middle section, and this is what it shows:

Top: What is recieved from the RF reciever
Bottom: What is send by the RF sender

- And from left to right:

First the R is creating Noise (what makes it do this, I also know now, but more about that in another post)

Then, The S is sending a High and  Low, just the right length not to be recognized as serial input. This stops the noise, and serial TR/RX is going on, without problems, all bits are recieved.

Finally, after 2 bits are send and recieved without problems, the R-side responds with a sound, resulting in a wave on that part.

Year, baby!

A soundcard can easily handle the logic 5V as in, and you have 2 channels on your soundcard. It is that easy - you can compare analoge current with alternating current, see what PWM does to your motor, see how a magnet creates a spike somewhere else etc!!

Cool :D 

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If my memory is still good, then the sound card is expecting a inut voltage range of +/- 1 volt. You may need a voltage divider to protect the circuit. Google "sound card oscilloscopes" for more info.

As had been mentioned, the frequency response is in the audio range, good enough to view lower baud rate serial data or IR codes.

voltage divider is good to obtain the right sensitivity

but voltage clipper with anti-parallel diodes is needed for protection