4 buttons / 4 leds over 2 wires

Hi everyone,

I would like to build a footcontroller (4 footswitches, 4 leds) which is connected with a standard jack cable (mono, 2 wires) to a main controller which contains the arduino etc.

It looks like this is possible because I see Electro Harmonix doing it with their HOG + footcontroller and 2880 + footcontroller. Both have 6 buttons and 6 leds and draw power from the main effect pedal, so no additional power supply, and connected with a jack cable.

I really have no idea how that is possible, any thoughts? Can a certain IC do the trick?

Both have 6 buttons and 6 leds and draw power from the main effect pedal, so no additional power supply, and connected with a jack cable.

If that truly is the case, which I doubt, the way it must work is that the jack carries the power and on top of that the signals are modulated at a high frequency and connected to the power by a DC blocking capacitor. Then on the other end the signal is extracted and decoded. This means there needs to be some signal processing electronics inside the pedal. Having buttons and LEDs means that communications has to work both ways so that would mean half duplex communication, based on a single channel. That rules out I2C and SPI.
That in turn would suggest some sort of processor in the peddle and the main box.
Are you sure there is not a battery in the peddle?

Thats called phantom power and is widely used in the audio industry, usually for powering mics, foot pedals like the OP said, and some other things thake I dont recall now. As it is a footpedal, the phantom power provides +48V over the audio out jack of the foot pedal and then all the effects are done inside the footpedal using op-amps and filters and/or a digital signal processor(DSP), so it doesn't need any sort of data to be sent out of the footpedal, it makes everything inside it.

I used to work with Aston TV character generators.
Their QWERTY (and then some!) keyboard plus trackerball used to work over a single studio-standard BNC-terminated coax cable.
It had status LEDs too, IIRC, so it must’ve worked both ways.

Can’t imagine it was cheap.
Bulletproof, but not cheap!

Outch, not that simple apparently!

Links to one of the pedals I'm referring to: http://www.ehx.com/products/hog http://www.ehx.com/products/hog-foot-controller/instructions

"The Electro-Harmonix Foot Controller obtains all of its power from the HOG GUITAR SYNTHESIZER. Use only a standard 1/4” guitar cable to connect the Foot Controller to the HOG. A standard guitar cable has Tip and Sleeve conductors. The Foot Controller does not require batteries or an AC Adapter." EHX.com

Maybe I should look for a solution with a seperate power supply then? I'm still in the beginning stage of electronics, I'm pretty excited I'm able to use a multiplexer and a shift register if you catch my drift...