Electronic Esophagus

Parts

Electronics

Arduino- compatible microcontroller (Teensy-LC) Teensy-LC

A capacitive touch sensor (Adafruit MPR121) MPR121 Capacitive Touch Sensor

stepper motor driver (Pololu DRV8825) DRV8825 Stepper Motor Driver

stepper motor (NEMA-17, 200 steps/rev, 12V, 350mA) Stepper motor, NEMA-17, 200 steps/rev, 12V 350mA

Hardware

1 Aluminum Flex Shaft Coupler - 5mm to 8mm

1 Linear Ball Bearing - 8mm diameter

1 M8 x 250mm Fully Threaded Rod, 304 Stainless Steel, Right Hand Threads like this one

1 Linear Motion Rod 8mmx 250mm like these

1 M8-1.25 Hex Nut like these

3D Printed Parts

The 4 parts are currently available as STL and 3MF files. Download here

Software

Adafruit Tutorial

Arduino IDE

Teensyduino add-on

ArduSpreadsheet add-on

Assembly

Electronics

Fritzing schematic.

3D Printed Parts and Hardware

3D Printed Parts

3D printed parts 4 parts ("NemaMount," "MidBody," 20mLbody" and "Plunger").

Code

Arduino code is written in C/C++

//include relevant libraries 
#include <Wire.h>
#include "Adafruit_MPR121.h"
#include <AccelStepper.h>

//define MPR121 info
#ifndef _BV
#define _BV(bit) (1 << (bit)) 
#endif
Adafruit_MPR121 cap = Adafruit_MPR121();
uint16_t lasttouched = 0;
uint16_t currtouched = 0;

//define DRV8825 stuff:
#define dirPin 2
#define stepPin 3
#define motorInterfaceType 1

// Create a new instance of the AccelStepper class:
AccelStepper stepper = AccelStepper(motorInterfaceType, stepPin, dirPin);

//setup code here, to run once:
void setup() {
  stepper.setMaxSpeed(1000); //set max stepper speed in steps per second
  Serial.begin(9600); //start serial monitor
  while (!Serial) { // needed to keep from starting too fast!
    delay(10);
  } 
  Serial.println("Electronic Esophagus test start");  
  // Default address is 0x5A, if tied to 3.3V its 0x5B
  // If tied to SDA its 0x5C and if SCL then 0x5D
  if (!cap.begin(0x5A)) {
    Serial.println("MPR121 not found, check wiring?");
    while (1);
  }
  Serial.println("MPR121 found!");
  // to change threshold sensitivites (touched, released). Defaults are (12,6). Valuess from 0-255 = less-more sensitive. 
  cap.setThresholds(24, 12);
}

// main code here, to run repeatedly:
void loop() {
  // Get the currently touched pads
  currtouched = cap.touched();
 
  for (uint8_t i=0; i<12; i++) {
    // it if *is* touched and *wasnt* touched before, alert!
    if ((currtouched & _BV(i)) && !(lasttouched & _BV(i)) ) {
      Serial.print(i); Serial.print('\t'); Serial.println(" touched");
      // set the position to 0:
      stepper.setCurrentPosition(0);
       // Run the motor forward at 400 steps/second until the motor reaches 12 steps (~0.125 revolutions):
       while(stepper.currentPosition() != 12)
       {
        stepper.setSpeed(400);
        stepper.runSpeed();
        }
        delayMicroseconds(500);
    }
   
    // if it *was* touched and now *isnt*, alert!
    if (!(currtouched & _BV(i)) && (lasttouched & _BV(i)) ) {
      Serial.print(i); Serial.print('\t'); Serial.println(" released");
      stepper.setCurrentPosition(0);
      stepper.stop(); // Stop as fast as possible: sets new target
      stepper.runToPosition(); // Now stopped after quickstop
      delayMicroseconds(500);
    }
  }
  // reset our state
  lasttouched = currtouched;
  // comment out "return" line for detailed data from the sensor!
  return;
  // debugging info, what
  Serial.print("\t\t\t\t\t\t\t\t\t\t\t\t\t 0x"); Serial.println(cap.touched(), HEX);
  Serial.print("Filt: ");
  for (uint8_t i=0; i<12; i++) {
    Serial.print(cap.filteredData(i)); Serial.print("\t");
  }
  Serial.println();
  Serial.print("Base: ");
  for (uint8_t i=0; i<12; i++) {
    Serial.print(cap.baselineData(i)); Serial.print("\t");
  }
  Serial.println(); 
  // put a delay so it isn't overwhelming
  delay(100);
}

References

Dr. D-Flo. (2017, Feb 20). DIY Syringe Pump (Food 3D Printer - Part 1) [Video]. YouTube. [1]

Elizalde G & Sclafani A, Flavor preferences conditioned by intragastric polycose infusions: A detailed analysis using an electronic esophagus preparation, Physiology & Behavior 47: 63-67, 1990. [2]

Longley M et al. An open source device for operant licking in rats. PeerJ 5:e2981, 2017. [3]

Wijen B et al. Open-source syringe pump library. PLOS ONE 9(9): e107216, 2014. [4]

People

Marena Bass

Research Support

T32 DC000044, National Institutes of Health (NIH/NIDCD) Bass, Marena N Florida State University (FSU) Chemical Senses Training Program (CTP) Grant Award Role: Trainee (08/07/2019 - 08/06/2021)