Odour stimulator

An open reimplementation of a dual-channel olfactory stimulator (Raiser et al. 2017) for insect olfaction experiments. It delivers two precisely controlled odour streams, balanced by two clean-air streams, for stable flow with millisecond precision.

Ingredients

BeeHive boards:

Other components:

How it works

The stimulator runs two odour channels balanced by two clean-air channels. When an odour stream is switched in, a matched clean-air stream is switched out, so the total flow reaching the animal stays constant — this is what keeps the stimulus free of pressure and flow artefacts. Each stream is gated by a three-way Teflon solenoid valve (LHDA1233415H) feeding a custom 3D-printed polypropylene mixing block, chosen for its chemical inertness to odourants.

The valves are switched by two Spike & Hold boards, which briefly overdrive each solenoid so it opens in hundreds of microseconds — giving the millisecond timing precision the paradigm needs. The channel count is expandable: add valves and Spike & Hold channels for richer odour panels.

Typical uses include single-sensillum recordings, insect wind-tunnel flight and walking assays, and single-fly chambers.

Wiring

• Each three-way solenoid valve to a channel on a Spike & Hold board.
• Each Spike & Hold board to a mainboard data line, plus power and ground. Spike & Hold mode pairs with the 12V/24V boost converter for the overdrive pulse.
• Air lines route through the valves into the 3D-printed mixing block; the combined stream goes to the preparation.

Code

Each Spike & Hold board switches its Teflon valve exactly like any solenoid daughter board — a GPIO driven high then low. The BeeHive solenoid driver example shows the pattern (one output per valve):

from machine import Pin
import time

valve = Pin(2, Pin.OUT, drive=Pin.DRIVE_3)   # a Spike & Hold / solenoid output

valve.on()
time.sleep_ms(50)     # 50 ms pulse
valve.off()

A balanced odour pulse switches an odour valve in while switching its paired clean-air valve out at the same instant, so total flow to the animal stays constant. Sequencing the two odour channels and their balancers is application-specific; the per-valve control is the example above.

Results / notes

The stimulator reproduces the Raiser et al. (2017) design on open hardware, delivering balanced, millisecond-precise odour pulses validated with a PID (photoionization detector). Channels expand by adding valves and Spike & Hold boards.