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Maybe I Need A Speaker

If you are going to build electronic projects centered around creating a synthesizer, you need some way to output sound.

You’d think that would be obvious. So, while assembling an APC on the breadboard Friday, did I make sure I had one?

Nope. So, I had the full circuit built and ready to test. I went looking through my storage boxes of components to find one. No luck. I could swear I had one, but if I did the earliest I’ll find it will be tomorrow.

Disappointed, I figured I could test it by checking voltages. That didn’t work, as the rate was fast enough that my meter reported the average of many samples. Does my meter have hertz? Of course, but I didn’t think about that.

I did think using an LED might work. My previous work on a 555 timer-based circuit had been to use it in astable mode to provide a clock for digital circuits thanks to Ben Eater. The LED was just constantly on. I didn’t feel like getting the oscilloscope up and running Friday so I just put things up and called it a night.

You’d think having the oscilloscope set up would be a natural line of thinking when you’re building synthesizer projects as well. Look, I never said common sense was my strong suit.

A rapidly improved breadboard speaker

Saturday was pretty full. I knew I wouldn’t get to the project, but I wanted to be ready to go when I’d have time on Sunday. After trying MicroCenter for a speaker among their components for people experimenting with Arduinos, Raspberry Pis, and similar boards I hit Brandsmart.

I bought the little guy to the left. It’s a simple Bluetooth speaker and costs less than five bucks. I pried the bottom off and snipped the wires connecting the speaker to the internal electronics. Hooking this speaker up to my APC still provided no output. I’m not sure if I’m just not generating enough power to drive the speaker or not. I might whip up a simple amplifier based on a TL07x chip this evening, but I did not want to bother last night.

So, I ordered these speakers from Amazon, which will be here tomorrow. Hence the reason I won’t bother looking for the speaker I’m sure I have tonight.

Last night I set up the oscilloscope. That was also a bit of a challenge. My scope is a USB one from Owon, the VDS1022i. I had it working in the past on my low-end Dell laptop, but since the last time I used it, I have blown Windows off that laptop in favor of a text-only Linux environment. That necessitated setting it up on either the Windows laptop or the desktop. I went for the desktop. It was an unexpected adventure. It took four tries to load the driver, including removing and reinstalling the software for using the scope. I did finally get it running.

When I hooked up my first APC I saw the stepped square wave I expected. What did not behave as expected was the effect of the second potentiometer. I expected it to affect pulse width, which it did, but it would also cause breakpoints in audio frequency. I suspect this occurred when there was some ratio that synchronized the timers. I didn’t think to save any oscilloscope traces or I’d post them here. I’ll put that on the list of things to do tomorrow when I have the speaker. When I have it, I plan on building a second APC on the breadboard to test frequency modulation using one APC into another one.

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