There’s an old saying: Tell me and I forget, teach me and I may remember, involve me and I learn. I’m guilty of this in a big way — I was never much on classroom learning. But if I build something or write some code, I’m more likely to understand how it works and why.

Circuit simulation and software workbooks like Matlab and Jupyter are great for being able to build things without a lot of overhead. But these all have some learning curve and often use clever tricks, abstractions, or library calls to obscure what’s really happening. Sometimes it is easier to build something in a spreadsheet. In fact, I often do little circuit design spreadsheets or even digital design because it forces me to create a mathematical model which, in turn, helps me understand what’s really going on.

In this article I’m going to use Google Sheets — although you could do the same tricks in just about any spreadsheet — to generate some data and apply a finite impulse response (FIR) filter to it. Of course, if you had a spreadsheet of data from an instrument, this same technique would work, too.

# Never Mind The Sheet Music, Here’s Spreadsheet Music

Nothing says Rockstar Musician Lifestyle like spreadsheet software. Okay, we might have mixed up the word order a bit in that sentence, but there’s always Python to add some truth to it. After all, if we look at the basic concept of MIDI sequencers, we essentially have a row of time-interval steps, and depending on the user interface, either virtual or actual columns of pitches or individual instruments. From a purely technical point of view, spreadsheets and the like would do just fine here.

Amused by that idea, [Maxime] wrote a Python sequencer that processes CSV files that works with both hardware and software MIDI synthesizers. Being Python, most of the details are implemented in external modules, which makes the code rather compact and easy to follow, considering it supports both drums and melody tracks in the most common scales. If you want to give it a try, all you need is the `python-rtmidi` and `mido` module, and you should be good to go.

However, if spreadsheets aren’t your thing, [Maxime] has also a browser-based sequencer project with integrated synthesizer ongoing, with a previous version of it also available on GitHub. And in case software simply doesn’t work out for you here, and you prefer a more hands-on experience, don’t worry, MIDI sequencers seem like an unfailing resource for inspiration — whether they’re built into an ancient cash register, are made entirely out of wood, or are built from just everything.

Last time I showed you how to set up a reasonably complex design in a spreadsheet: a common emitter bipolar transistor amplifier. Having the design in a spreadsheet makes it easy to do “what if” scenarios and see the effects on the design almost immediately.

Another advantage that spreadsheets offer is a way to “solve” or optimize equations. That can be very useful once you have your model. For Excel, you need to install the Solver add-in (go to the Excel Options dialog, select Manage Add-Ins, and select the Solver Add-In). You might also enjoy OpenSolver. You can even get that for Google Sheets (although it currently lacks a non-linear solver which makes it less useful for what we need).

# Circuit Design? Spread The Joy

Accountants and MBAs use spreadsheets to play “what if” scenarios with business and financial data. Can you do the same thing with electronic circuits? The answer–perhaps not surprisingly–is yes.

Consider this simple common emitter amplifier (I modeled it in PartSim, if you’d like to open it):

In this particular case, there are several key design parameters. The beta of the transistor (current gain) is 220. The amplifier has an overall voltage gain of about 3 (30/10). I say about, because unless the transistor is ideal, it won’t be quite that. The supply voltage (`Vcc`) is 12 volts and I wanted the collector voltage (`VC`) to idle at 6V to allow the maximum possible positive and negative swing. I wanted the collector current (`IC`) to be 200mA.

# Using Excel To Watch Movies At Work

The Excel subreddit exploded earlier this week when redditor [AyrA_ch] shared his custom spreadsheet that allowed him to play video files on a locked-down work computer. How locked down? With no access to Windows Media Player and IE7 as the only browser (all plugins disabled, no HTML5), Excel became the unlikely hero to cure a 3-hour boredom stint.

Behind the cascade of rectangles and in the land of the Excel macro, [AyrA_ch] took advantage of the program’s VBA (Visual Basic for Applications) functions to circumvent the computer’s restrictions. Although VBA typically serves the more-complex-than-usual macro, it can also invoke some Windows API commands, one of which calls Windows Media Player. The Excel file includes a working playlist and some rudimentary controls: play, pause, stop, etc. as well as an inspired pie chart countdown timer.

As clever as this hack is, the best feature is much more subtle: tricking in-house big brother. [AyrA_ch]’s computer ran an application to monitor process usage, but any videos played through the spreadsheet were attributed to Excel, ensuring the process usage stayed on target. You can download it for yourself over on GitHub.