Introduction: Auto Mushroom Shotgun Chamber

This is an instructable for an automatic humidity and fresh air exchange timer chamber for fruiting mushrooms. It is fully USB powered and requires only one 1 amp USB port to power the whole thing. You may also get some sort of light source as certain mushrooms need it to fruit, but indirect sunlight also works so I will exclude the lighting from this intructable for simplicity sake.


5V USB ultrasonic humidifier(search 'cowboy cap humidifier' if link stops working):

Cowboy Cap Humidifier

5v relay:

Arduino Nano:

5V 3 or 4 prong computer fan(This one is a bit pricier but its super quiet so i recommend it):

Step 1: Wiring

Here is a rough schematic (you will need to open up the plastic part of the humidifier USB to get to the electric components).

Step 2: Code

Here is the Arduino code for this project(I've attached the ino file):

int relay = 8; // define humidifier relay switch pin

int fan = 4; // define fan control pin

void turnRelaySwitch() {

digitalWrite(relay, HIGH);


digitalWrite(relay, LOW);



void setup() {

pinMode (relay, OUTPUT) ; // relay switch as output interface

digitalWrite(relay, HIGH); // relay switch as digital input

analogWrite(fan, 0); // fan switch as analog input


void loop() {

turnRelaySwitch(); // humidifier on for 5 min


turnRelaySwitch(); // humidifier off, rest for 15 min


analogWrite(4, 255); // fan on for 10 min


analogWrite(4, 0); // fan off


Step 3: Starting Up

The humidifier needs to soak for a bit in a container of water, and I used a metal grate to put the blocks of mushroom mycelium on in case pins start growing from the bottom. It's also a good idea to put a layer of perlite on the bottom of your container to absorb excess moisture. You should drill holes for air circulation, humidifier wire and a large one to fit the fan through so air can blow into the chamber. When starting up the device, you might need to reset sometimes so that the humidifier is running properly. The delay times in the code can be altered depending on your container setup and mushroom type, some more air exchange or humidity might be required.