Hidden Agenda Is an Effects Pedal for Computer Keyboards and Mice

A clean electric guitar signal doesn't sound particularly interesting. It is like an acoustic guitar, but with less warmth and resonance. Most of the electric guitars you hear in rock, pop, and metal music use effects, which alter the audio signal in some way. The most famous and widespread is distortion, which mimics the effect of an over-driven tube amplifier to impart noise into the signal. But there are many, many others. Guy Dupont took that idea and applied it to computers by building an effects pedal called Hidden Agenda that alters keyboard and mouse input.

That probably doesn't make much sense to you, because mice and keyboards are digital input devices and there isn't any analog signal to modify. How does one distort a signal from a mouse that tells a PC to move the cursor to a specific coordinate? Dupont had to get creative in order to translate the abstract idea of different effects into algorithms that could apply to computers and mice.

For example, one of the effects that Dupont created for mouse input is reverb. In the audio world, reverb is a bit like echo — though echo is actually another distinct effect. Reverb sounds like a loud sound in a large room with hard walls, like if you yelled inside of a racquetball court. To give a mouse reverb, Dupont programmed the cursor to have momentum. When turned up, the cursor keeps moving for a noticeable distance after the user stops moving the mouse.

There are several of these "effects" that apply to the mouse, but Dupont also programmed some for keyboards. The pitch shift effect, for instance, moves up or down the unicode list when the user presses a key. With it turned up slightly, pushing the "b" key will result in the letter "c" appearing. With it turned down slightly, "a" will appear. When in harmonizer mode, it will type all three letters like a barbershop quartet singing in unison.

On the hardware side, Dupont achieved this using a custom PCB populated with a Raspberry Pi RP2040 microcontroller. It reads the input from the mouse or keyboard through USB, adjusts that according to the selected effect, and then sends the modified input to the PC through USB. As far as the PC knows, it is receiving standard USB HID input. That custom PCB includes a rotary encoder and a stomp switch, just like the kind you'd find on a guitar effects pedal. Those all fit into a 1590B pedal enclosure with some neat artwork on top.

Hidden Agenda doesn't have much practical use, but it is a creative project and we love seeing this kind of outside-the-box thinking.