It used to be that when it came to logic functions and logic-based modules, I just didn't get it. I really couldn't understand why something called "logic" made me feel so stupid. I'm logical, I like efficient, sensible, reliable and predictable thoughts and things. Well, I am still by no means an expert at logic functions, I think I've finally started to crack the code, at least I hope.
Logic modules take a binary gate signal (1s and 0s; logic-ally termed "high" or "low") on a given input channel. When certain combinations are met with multiple input channels simultaneously, you can get an output. This depends on the selected logic mode (there are many of them, and each mode acts differently), and is determined by what's called a "truth table," which lays out the requirements, the rules, for each logic mode. For example, if you have two inputs, one high (1) and one low (0) in AND mode, then the output is "low," meaning that it's off, meaning that there is no voltage at the output. AND mode needs both inputs to be high (1s) for the output to be high. If you're in OR mode with the same situation for those two inputs (one high, one low), the output will go high, there will be voltage other than 0 at the output. OR just needs one channel, it doesn't matter which, to be high, to have the output go high. You can see these requirements in the logic truth table to understand it a bit more, so grab a coffee, we're just beginning…
The more channels, the more inputs, and the more modes there are available, the more potential variation, the more potential for complexity there is. Add some switches to the inputs for a little hands-on experience, and add the ability to quickly switch logic functions with those very same hands, and you've got a little say in the matter, where the potential is at your fingertips. Potential for rhythmic mayhem, melodic mayhem, and modulation mayhem. Or no mayhem at all. Or maybe just a little mayhem; it's your choice. That's what we're getting with BTMX, Schlappi Engineering's latest logic module: the potential for mayhem.
In BTMX, there are four logic modes: ADD, AND, OR, and XOR. With eight input channels (1-8) and four paired Gate output channels (1+5, 2+6, 3+7, 4+8), and a Stepped output (the summed culmination of the Gate outputs), BTMX has (potentially) a lot going on. Basically, BTMX is four channels of two-input logic gates, where the logic function is selectable. Conversely, another way one can view BTMX is that of a variably configured logic module that will take two nibbles for its input.
For a bit of clarity, courtesy of Sparkfun:

“Each 1 or 0 in a binary number is called a bit. A group of four bits is called a nibble, and eight bits makes a byte.”

It definitely does get confusing, but it's possible to get comfortable with both the operation of logic, and its terminology, though in all honesty, it's a lot easier to use logic than it is to understand it. At least I found this to be the case in the beginning.
A trigger, gate, bit, byte, nibble, or having the toggle switched up for a given channel's input, gets that channel to go high at the input, and emits a fixed output voltage (channels 1+5 = +5.3V, 2+6 = +2.64V, 3+7 = +1.32V, and 4+8 = +0.66V) at its corresponding output. When it comes to each channel outputting a voltage at the Stepped out, that's determined by whether or not the requirements are met via the truth table, which depends on the logic function. The Stepped output is the heart of BTMX, and is good for pitching a VCO, harsh modulation CV for whatever use you can think of, and creating changes that can go from nice and smooth to chaotic and haywire. The Gate outputs are great for creating rhythms, triggering external parameters/effects off and on, and so on.
Most logic modules are pretty hands off; patch things in, patch things out, slowly walk away, usually confused. This brings up the sweet thing about BTMX, the thing that sets it apart; the ability to switch modes and mute channels with the toggles—the ability to muss things up by hand. Even when I had little to no idea what I was doing, and had to play catch-up to figure out the reason why something was happening (or not), it was pretty easy to get funky rhythms, robotic melodies, or anything where stepped voltages and oddly timed gates could wreak havoc. Sometimes I would patch things up without changing the logic function until I got good movement, and only then would I switch functions to see how things changed, how the modes determined each output's on/off status.
For basic melodic-ish function, patching the Stepped out into a 1V/Oct input of a VCO gets a repeating sample and hold type of functionality, similar to what you'd get with a mutating step sequencer with just a few steps. This all depends on what is patched into each input, what mode is selected, and how the toggles are and all that, but that's par for the course. The resulting personality of the melody reminded me of what an 80s IBM mainframe would sound like if it could talk. It's more than just 1s and 0s (well, technically…), but not much more; maybe throw in a few fractions (nibbles, really) and you'd be there. Patch this same thing into a CV input to modulate a filter cutoff or resonance or something, and the results can be harsh, armed forces type of regimentation. Remember, there's no smooth transitioning—no slew or glissando—for the changes in voltage; it's abrupt! You can do things with BTMX like burst generation and trigger/gate combiners, creating what sounds like semi-random triggering, but where BTMX really shines is when used for drum/percussion duties.
Patching each Gate output into percussion-based modules can, and will, yield some crazy off-rhythms. Add in some twitchy toggling, and variations on the rhythm abound. It's good fun to patch BTMX all up with LFOs, Schlappi's Nibbler, etc., for triggering, and patching the Gate outs into a kick, hat, snare, clap (?) and with the Stepped out going into some sort of melodic module. Mutating beats and melodies, yet still somewhat rhythmic and in cahoots with each other, will keep you on your toes. One thing to note: individual output voltages aren't summed to the Stepped output, no output on BTMX will ever exceed +10V: You won't blow anything up.
With status LEDs for each input and output, letting you know if it's being triggered (flashing LED with the triggering), or just on (LED is constantly on), and LEDs that light up for each Gate output when they pass voltage, there are good visual indications throughout, which is really helpful.
I mentioned using BTMX with Schlappi Engineering's Nibbler, and it really seems these two are meant to be neighbors, borrowing sugar, lawn tools, and helping each other fix broken stuff. Inputs, outputs, the RESET button on Nibbler…it's good fun to pair the two modules up, flip some toggles, and smash that RESET on Nibbler. A word of caution: a lot of the time when switching things around you'll be just as likely to halt the whole shebang—no sound or movement at all—as you will be to stumble onto something super cool and intriguing. It's all in the name of experimentation, so buckle up and enjoy the ride.

Price: $193

schlappiengineering.com