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Controls and I/O

This page explains how Spikeling’s physical connections work: what each connector carries, how to cable units together, and how to avoid the most common wiring mistakes.

Spikeling uses 3.5 mm TRS (stereo) jacks throughout. The same cable type can carry both an analogue signal and a digital event marker, plus ground.

If you want a high-level tour of the board and controls, see: Device overview.

The TRS convention (Tip / Ring / Sleeve)

Each Spikeling TRS jack carries:

  • Tip (T): digital signal (spike events / PWM)
  • Ring (R): analogue signal (typically Vm or stimulus analogue waveform, depending on jack)
  • Sleeve (S): ground (0 V reference)

This design lets you carry the information needed for most electrophysiology-style teaching tasks in a single cable: an analogue trace and a digital timing marker.

Ground matters

The sleeve is not optional. Most “mystery noise” and “flat line” issues happen when the ground reference is missing, intermittent, or swapped.

What “digital” means on Spikeling

The digital line (Tip) is used for event timing:

  • spike events (axon output / synaptic inputs)
  • stimulus PWM (pulse width modulation) for LED stimulation
  • synchronisation between recordings or units

Digital events are especially useful when analysing data later: they allow you to align traces to a stimulus onset or to detect presynaptic spike timing precisely.

What “analogue” means on Spikeling

The analogue line (Ring) carries a continuously varying voltage representing one of:

  • Vm (membrane potential output, read by a second unit or by an oscilloscope mapping to 3.3v)
  • stimulus waveform (generated by the board or GUI, meant to be plugged on the current input port. External waveform generator mapping current to 3.3v can also be used)

Analogue is what you look at as a trace in the GUI (and later in CSV).

Connector roles (conceptual map)

The exact jack labels may vary slightly by revision/board silkscreen, but the roles are consistent:

Outputs

  • Synaptic output: analogue = Vm (-110 - 100mV -- 0 - 3.3v); digital = spike events
  • Stimulus output: analogue = stimulus waveform (-100 - 100% -- 0 - 3.3v); digital = Stimulus PWM (12bits)

Inputs

  • Synapse input 1 / 2: accepts a TRS feed from another unit’s axon output
    (analogue = Vm; digital = spike events)
  • Current input: accepts an analogue waveform used as injected current drive
  • Photodiode: not a connector itself, but a physical input driven by light (often using the LED cable)

Common cabling patterns (what users actually do)

1) Make a two-unit network (presynaptic → postsynaptic)

Goal: Use one Spikeling unit to drive another via a synapse.

Cable: - Unit A Axon output → Unit B Synapse input 1 (or 2)

What travels on the TRS: - Tip: spike events (trigger synaptic currents) - Ring: presynaptic Vm (used for visualisation only) - Sleeve: shared ground reference

Then set the Synapse gain (±) on unit B: - positive = excitatory - negative = inhibitory

(See also: Synapses and inputs and Network with two units.)

Goal: Deliver reproducible light stimulation to the photodiode as a retina-inspired sensory pathway.

Cable: - Stimulus output → LED cable → aim LED at photodiode

The LED cable lets you use either: - the on-board square stimulus (frequency/strength knobs), or - the GUI stimulus generator (steps, sine, chirps, noise, etc.)

to drive the LED with precise timing.

Then use the Photo-gain potentiometer to set: - magnitude of the photodiode pathway - polarity (positive vs negative sensory drive)

3) Use the stimulus output as injected current (stimulus → DC input)

Goal: Treat the stimulus generator like a function generator for injected current.

Cable: - Stimulus output → Current injection / DC input

This is useful when teaching protocols such as: - steps (baseline → constant injection → baseline) - oscillatory drive (sine/triangle) - sweeps (chirps / ZAP-style probing) - noise injection (controlled variability)

Cable and adapter recommendations

Use real stereo (TRS) cables

Use 3.5 mm stereo TRS male–male cables (two black rings on the plug).

Avoid: - mono TS cables (one ring) if you expect both digital + analogue - TRRS headset cables (three rings), which can map contacts differently

Keep cables short when teaching

Short cables reduce pickup and make demonstrations more stable.

Label your classroom cables

For teaching at scale, label cables by function: - “AXON → SYN” - “STIM → LED” - “STIM → DC”

This saves a lot of time during labs.

Quick troubleshooting (I/O specific)

“No signal / flat line”

  • confirm you are using a TRS stereo cable
  • check the plug is fully seated (TRS jacks can feel “in” before they click)
  • confirm the correct port (axon vs synapse vs stimulus vs DC)

“Signal looks noisy / unstable”

  • confirm ground (Sleeve) is present and not intermittent
  • shorten cables
  • keep LED cables away from analogue signal cables if possible

“Synapse does nothing”

  • check you connected axon output → synapse input
  • confirm the presynaptic unit is actually spiking (LED/buzzer helps)
  • increase synapse gain magnitude and confirm polarity (±)