User Manual

Powering On

When powered from batteries, please use the sliding switch to safely power off the device. It will completely disconnect the (+) pole, so no significant energy is drawn from batteries. It is perfectly safe to power the board via USB from a standard 5V power source without removing batteries (also plug/unplug the USB cable even while music is playing). This is a good way to extend battery life when you have adaptor or USB port at hand.

If your battery pack also connects to "BAT+3V" pad (leading to MCU's VBAT pin / SRAM back-up voltage), it is not disconnected at any time, to preserve user generated content or settings (this only draws very little power from batteries, having virtually no effect on their life time).

The PWR (power) LED should light up, and RDY (ready) should blink in 0.5sec intervals.

When powering via USB cable, the sliding switch does not turn device off, but it changes between normal mode (at ON position), and programming mode (at OFF). This setting is "checked" at the time of connecting power (if no batteries present), and/or pressing RST (reset). For example, if you have a bare board and it is set to OFF, and you apply power from USB, it will get into programming mode. RDY will not blink, and other LEDs will lit up in a characteristic pattern.

In this situation, to get the board running normally, not only you need to set switch to ON, but also press RST button.

Selecting a Channel

Every channel's code consists of one or more numbers between 1 and 4, so they can be typed on the four-buttons keyboard. For example, to select channel #1234, press four buttons in a row, then press SET.

In some channels, SET can select an alternative mode, depending on whether you just press it or hold it for a second. All basic song-playing channels can run in Low-pass or High-pass mode. Normally, the Low-pass is selected, with the exception of channel #1 which uses High-pass as default. So, if you - after keying in the channel number - hold SET for a second, instead of just pressing it briefly, an alternative mode is selected (in this case, High-pass filters instead of a default Low-pass).

Currently Available Channels (version 0.192)

The channels marked VIP are work in progress and may not run well. Some numbers are also reserved for future use and currently do nothing, but they are listed so you know what to expect there.

  • 1: Demo song #1 with melody and high-pass filters as default
  • 2: Demo song #2 with melody - "Freedom of Creation" advert
  • 3: Picks random song out of basic demo songs (#11,12,13,22,23) and play it with low-pass filters
  • 4: Demo song #21 - "Ghost in the Shell" - used in "Assembly machines - Making of Synth" video (chords only)
  • 11: Pure white noise
  • 12: Non-interactive, slowly evolving low-pass filters - "Song of Wind and Ice"
  • 13,14: Non-interactive, static low-pass filters "Distant Ocean"
  • 21-24: Noise/resonance effects controlled by sensors, four different settings:
    • 21: Waves of the Sea
    • 22: Nostromo
    • 23: Alien Spaceship
    • 24: Combined (4 levels - each sensor different cut-out frequency)
  • 31: Theremin-like behaviour driven by magnetic ring (VIP)
  • 32: Theremin driven by sensors (VIP)
  • 33: DCO Synth, 24 oscillators bound in parallel, directly controlled by sensors
  • 34: DCO Synth, with locking mechanism and MIDI. When you press SET, parameters are locked, then you can hold buttons 1-4 to unlock individual one and affect it by related sensor. The first parameter is pitch, and can be controlled by a midi keyboard if connected.
  • 41-44: Custom song programming modes. First, select how many chords you want by pressing buttons 1 and 2. You can have from 1x1 to 8x4 chords total. Press button 4 to confirm. Then, input individual chords:
    • 41: Input chords by buttons: 1/2 to select a chord, 3 to confirm. PLEASE DO NOT USE FOR NOW, there is a bug that causes a nasty noise to be sent into headphones. Sorry for this, will be fixed in next version.
    • 42: Input chords by magnetic ring, by selecting individual notes one by one. After a note is held for one second, it is remembered. After three notes are set, it moves to next chord and waits for new notes. When enough notes for pre-selected amount of chords is input, playback starts (VIP / Possible bug: it does not start playing)
    • 43: Input from microphones - works similar to previous mode, but notes are recognized from environment. You need a clear source of sound to get good results (VIP)
    • 44: Input from pickus/line-in, works similar to previous mode, but notes are recognized from attached guitar or other signal source (VIP)
  • 111: Plays recently generated song (VIP - user data is not yet backed up to SRAM)
  • 112: Plays recently generated song with melody, if present (VIP)
  • 113: Play notes received from the Gecho App, using sampled instrument "toy box"
  • 222: Generate random chord progression - as explained here
  • 231: Simple drum kit - four samples, controlled by sensors
  • 232: Simple drum kit with echo
  • 233: Simple drum kit over song #2 - for tutorial and demonstration video
  • 234: [reserved] Simple drum sequencer (VIP)
  • 314: Songs of the Pi - picks a random position within first 100,000 digist of Pi and start generating chord progressions from there
    • 314[...]: More buttons pressed allow to select a particular position within decimal representation of Pi, starts generating a song from there
  • 321: Directly listen to signal coming via IR sensors. You can hear for example buzzing from IR sensor in your mobile phone, or TV remote
  • 322: Directly listen to signal coming from magnetic sensors, this may require strong enough alternating field to hear something (e.g. rotating magnet will produce quiet humming)
  • 323: All LEDs test (for PCB/soldering testing)
    • 3231: Lit up each LED one by one (helps discover solder bridges)
    • 3232: Lit up all LEDs then turn off each one by one (helps discover solder bridges)
  • 324: Magnetic sensor calibration test - red and white rows react to a full range of magnetic sensor influenced by e.g. mangetic ring
  • 331: Notes recognition - Goertzel detectors or auto-correlation test via microphones
  • 332: Notes recognition - Goertzel detectors or auto-correlation test via piezo pickups/line-in input
  • 333[...]: Access code lock for Gechologists part of the website
  • 341: Direct monitor of unaltered signal from microphones
  • 342: Direct monitor of signal from microphones, with echo
  • 343: Direct monitor of unaltered signal from pickups/line-in
  • 344: Direct monitor of signal from pickups/line-in, with echo
  • 1122: All drum samples test - plays four samples in sequence
  • 1211: CV direct notes test
  • 1212: MIDI out test - will transmit a few notes in sequence
  • 1213: [reserved] MIDI record and playback test (VIP)
  • 1214: CV/Gate test - CV1 controls voice, CV2 controls drum sample (VIP)
  • 1223: MIDI HW signals direct test - if you wire OUT to IN (plus to plus, minus to minus), pressing button 1 should make orange LEDs go off
  • 1234: Quick test for all buttons and LEDs
  • 4111: Demo song #11 - extended version of #1 (chords only, no melody)
  • 4112: Demo song #12 - "Canon in D" by Johann Pachelbel
  • 4113: Demo song #13 - random composition by Mario
  • 4114: XMAS Song, melody played by a sampled instrument (toy box), for tutorial with code samples
  • 4121: Demo song #21 - "Ghost in the Shell" - used in "Assembly machines - Making of Synth" video (with melody)
  • 4122: Demo song #22 - "Blade Runner - Rachel's Song" (chords only, no melody)
  • 4123: Demo song #23 - random composition by Mario
  • 4141: Slowly changing A minor and major chords plus single notes
  • 4142: Continuous A minor chord
  • 4143: Continuous A major chord
  • 4144: Continuous note A over more octaves

Buttons during Play

Normally (and in most channels) the buttons 1-4 control various parameters:

  • Button 1: Decrease headphones volume
  • Button 2: Increase headphones volume
  • Button 3: Cycle through various delay lengths - press it again to get to next setting (initially, it is set to 0.5s):
    • 3/4s (0.750)
    • 1s
    • 1.25s (currently maximum with stereo at 22.5kHz sampling rate)
    • 1/3s (0.333)
    • 1/4s (0.250)
    • 1/6s (0.167)
    • 1/8s (0.125)
    • 1/12s (0.083)
    • delay off (useful for recording, if you want to apply it later)
    • back to default 1/2s
  • Button 4: Switch between microphones and pickups input (initially it is set to microphones)

However, if you press SET during play, you get access to more settings. There are four groups of settings, press SET more times to select a particular group, then use buttons 1-4 to change the desired parameter. Row of red LEDs is used to indicate the current level of a particular setting between its minimal and maximal value.

If you don't change anything for 3.5 seconds, this mode completes and buttons revert back to normal operation.

Settings Group 1 - Equalizer:

  • Button 1: Decrease treble
  • Button 2: Increase treble
  • Button 3: Decrease bass
  • Button 4: Increase bass

Settings Group 2 - Internal volumes:

  • Button 1: Decrease OpAmp mixing volume - this affects sensitivity of microphones or pickups input. The setting changes slower than others as there is wider range to cover, you'd probably need to hold the button for longer time to observe any impact
  • Button 2: Increase OpAmp mixing volume (in a similar manner as previous one)
  • Button 3: Decrease Master volume - this is the analog volume after DAC/DSP block, affected by limiter
  • Button 4: Increase Master volume

Settings Groups 3 and 4 [VIP]

These settings are currently not implemented, but in future things like a variable tempo, or turning sensors & LEDs on and off (e.g. to conserve power) will be here.


Nice to get the Geckosynth today. Operation was not initially clear to me, but I'm figuring it out by experimentation. It's obvious you've put a lot of work into this.

IMO some more info is needed in the manual
* It seems I have to hit reset in order to select a new channel. Is that correct?
* Initially not clear which button is #1 (left or right) and whether button presses are sequential or simultaneous
* Many of the channels are overly microphonic for use on speaker. At first, I mostly had runaway feedback until I found the item of switching the mic input with button #4, Or using headphones.


Hi Gary, Thank you for your valuable feedback!

Yes, Reset button acts like a "stop". In previous firmware the playback was stopped by holding SET but that did not seem practical (mainly after adding extra settings which are invoked by SET button while playing).

Hope the second animated GIF now explains how to key in a channel.

Yes, it is not really intended to be used with external speakers for this reason, apart from channels which don't use microphones at all, e.g. from #11 to #34... But I see there might be need for it. In next firmware version it will remember these settings, so you don't need to press #4 every time (the same for volumes etc.), also user-content - chord progressions and melodies programmed in (#41-44) or uploaded via app, and also automatically generated random and semi-random songs (#222,#314) will be preserved during reset and power off.