Fab Academy 2018 - Thierry Dassé
I have chosen to make a board with a force-sensing resistor. Resistance value of this sensor depends of pressure or weight.
I designed a board on kicad, with two inputs : a FSR sensor and a switch button wich can be usae to turn the device on and off
or to calibrate the sensor.
As FSR sensor is a through hole component, I made a through hole footprint but with engraved copper on the front layer.
So, I won't need a double side board. I'll try to sold it on the front.
On my hello board, my ftdi header is a bit weeak. So, I also decided to make a through hole footprint to it.
Emma explained me that FSR pin are flat, so I will be able to sold it on a SMD pad and don't need holes.
So, I wanted to modify my board witout redoing all. On Kicad, you can do it by :
After, I decided to add a green led on the board on pin 5 (PB2). It can be useful to blink when events occurs in debugging session.
Complete kicad files and standard gcode for milling
I heard about FlatCam and wanted to try it to generate gcode for my board.
First, in Kicad, I plot my board (F.Cu and Edges.Cuts layers) in gerber format after placing a Drill and Place Offset. I also generate a drill file.
On FlatCam, I open F.Cu.gbr and Edge.Cuts.gbr gerber files and .drl drill file.
After double click on F.Cu or go to selected tab, I set parameters (in mm):
Then, click on generate. It creates a .gbr_iso file with wich you can export a gcode file.
For Edge cuts, parameters are:
Then, click on generate Geometry. It creates a .gbr_cutout file in wich you have to set other parameters :
Then you can export a gcode file.
I did the same for drill file setting depth to -1.7mm.
I am in EchoFab (Montreal) this week and will engrave my board on a different CNC I usually use.
First, I had a look at gcode to see how it's written.
gcode header is:
G21
G90
G94
F3.00
G00 Z2.0000
M03
G4 P1
F3.00 is linear speed when mill is milling. As I didn't know thix CNC unit system, so I tried in the air. Moving were too slow, so I change the value until it seems to be good.final value I keep is 80.0
M03 is to start spindle. As spindle has to be start by hand, I simplified the gcode header in:
G21 (coordinates are in mm)
G90 (commands are in absolute coodinates)
F80.00 (linear speed)
G00 Z2.0000 (goto z=2 mm)
Because, I am not in Paris, I didn't have an easy access to multimeter or other control devices.
So, I made different programs to control my board and see if all work right before making my final program.
Led test
/*
* input device
* led test : just blink twice a second
*/
const int ledPin = 8;
void setup() {
pinMode(ledPin, OUTPUT);
}
void loop() {
digitalWrite(ledPin, HIGH);
delay(500);
digitalWrite(ledPin, LOW);
delay(500);
}
Switch test
/*
* input device
* Switch test : turn the led on when switch button is pressed.
*/
const int ledPin = 8;
const int switchPin = 3;
int switchState = 0;
void setup() {
pinMode(ledPin, OUTPUT);
pinMode(switchPin,INPUT);
}
void loop() {
switchState = digitalRead(switchPin);
if (switchState) {
digitalWrite(ledPin, LOW);
} else {
digitalWrite(ledPin, HIGH);
}
}
FSR test
/*
* input device
* fsr test : make the led blink faster when you press the FSR sensor.
*/
const int ledPin = 8;
const int fsrPin = 7;
void setup() {
pinMode(ledPin, OUTPUT);
}
void loop() {
int value = analogRead(fsrPin);
if (value==0) {
digitalWrite(ledPin,LOW);
} else {
value = map(value,0,1023,500,20);
digitalWrite(ledPin,HIGH);
delay(value);
digitalWrite(ledPin,LOW);
delay(value);
}
}
/*
* FSR 1.0
* send a value twice a second
*/
#include <SoftwareSerial.h>
#define rxPin 0
#define txPin 1
const int ledPin = 8;
const int fsrPin = 7;
SoftwareSerial serial(rxPin,txPin);
void setup() {
pinMode(ledPin, OUTPUT);
serial.begin(9600); //open serial communication
}
void loop() {
int value = analogRead(fsrPin);
serial.println(value);
digitalWrite(ledPin,HIGH); // make a flashlight when sending a datastrong>
delay(20);
digitalWrite(ledPin,LOW);
delay(980);
}
/*
* FSR 2.0
* turn off and on with the switch button
* if on, send a value twice a second
*/
#include <SoftwareSerial.h>
#define rxPin 0
#define txPin 1
const int ledPin = 8;
const int fsrPin = 7;
const int switchPin = 3;
int switchPrevious = 1;
int switchState = 0;
int isOn = 1;
SoftwareSerial serial(rxPin,txPin);
void setup() {
pinMode(ledPin, OUTPUT);
pinMode(switchPin,INPUT);
switchPrevious = digitalRead(switchPin);
serial.begin(9600);
}
void loop() {
switchState = digitalRead(switchPin);
if ((switchState == 0) && (switchPrevious == 1)){
isOn = 1 - isOn;
}
if (isOn) {
int value = analogRead(fsrPin);
serial.println(value);
digitalWrite(ledPin,HIGH);
delay(20);
digitalWrite(ledPin,LOW);
delay(480);
} else {
delay(20);
}
switchPrevious = switchState;
}
In the third version, the program answer serial commands from the computer instead of switch button states
/*
* FSR 3.0
* answer to serial command:
* R : read return fsr value
* L : listen return fsr value twice a second
* S : stop listening
*/
#include <SoftwareSerial.h>
#define rxPin 0
#define txPin 1
const int ledPin = 8;
const int fsrPin = 7;
int isOn = 0;
SoftwareSerial serial(rxPin,txPin);
void fsrSend() {
int value = analogRead(fsrPin);
serial.println(value);
digitalWrite(ledPin,HIGH);
delay(10);
digitalWrite(ledPin,LOW);
delay(10);
}
void setup() {
pinMode(ledPin, OUTPUT);
serial.begin(9600);
}
void loop() {
if (serial.available()) {
char inChar = (char)serial.read();
switch (inChar) {
case 'R':
fsrSend();
break;
case 'L':
isOn = 1;
break;
case 'S':
isOn = 0;
break;
default:
serial.println("error");
}
}
if (isOn) {
fsrSend();
delay(480);
}
}
On the final version, I also had a calibration command.
You just need to put a weight on your sensor and use 'C' command
or press the switch button and current weight is scale to 1,000 units until you don't recalibrate.
/*
* FSR 4.0
* answer to serial command:
* R : read return fsr value
* L : listen return fsr value twice a second
* S : stop listening
* C : calibrate
*/
#include<SoftwareSerial.h>
#define rxPin 0
#define txPin 1
const int ledPin = 8;
const int fsrPin = 7;
const int switchPin = 3;
int switchPrevious = 1;
int isOn = 0;
int calib = 1000;
SoftwareSerial serial(rxPin,txPin);
void fsrSend() {
int value = analogRead(fsrPin);
serial.println(map(value,0,calib,0,1000));
digitalWrite(ledPin,HIGH);
delay(10);
digitalWrite(ledPin,LOW);
delay(10);
}
void fsrCalibrate() {
int value = analogRead(fsrPin);
if (value >0) {
calib = value;
}
}
void setup() {
pinMode(ledPin, OUTPUT);
pinMode(switchPin,INPUT);
switchPrevious = digitalRead(switchPin);
serial.begin(9600);
}
void loop() {
if (serial.available()) {
char inChar = (char)serial.read();
switch (inChar) {
case 'R':
fsrSend();
break;
case 'L':
isOn = 1;
break;
case 'S':
isOn = 0;
break;
case 'C':
fsrCalibrate();
break;
}
}
int switchState = digitalRead(switchPin);
if ((switchState == 0) && (switchPrevious == 1)){
fsrCalibrate();
}
if (isOn) {
fsrSend();
delay(480);
}
}
