SPST Spontaneous Action

[K5BLZR]

I'm using arduino code to create a digital gas gauge. Basically a flow sensor in the fuel line emits pulses which have been calibrated to be proportioned to a volume reading. That volume is then subtracted from a constant representing the gas tank's full volume. This "difference" is then displayed on an HT16K33 display. All of that works fine, I am just having difficulty with an on/off switch. Since the circuit runs off of the car battery and needs to stay on constantly so that the difference reading is not lost between power cycles, I want to turn off the display and reduce the mAh draw. (I am aware of EEPROM but its short hardware lifetime will not work for my application, any other non-volatile memory suggestions?) I have an SPST switch connected to Pin 3 and GND, however whenever I flip the switch sometimes the display goes on/off and other times it randomly flashes over constant or irregular time intervals. Very new to code so any debugging is appreciated.

#include "HT16K33.h"

HT16K33 seg(0x70);

uint32_t start, stop;

int sensorPin = 2;
int FullTank = 31.00;
volatile long pulse;
float volume;
float difference;
const int switchPin = 3;
int switchState;

void setup() {
  Serial.begin(115200);

  Wire.begin();
  Wire.setClock(100000);
  seg.begin();

  seg.displayOn();
  Serial.println("displayTest()");
  seg.displayTest(1);
  seg.displayOff();
  delay(1000);
  seg.displayOn();
  seg.displayColon(false);
  seg.setBrightness(5);

  pinMode(sensorPin, INPUT);
  attachInterrupt(digitalPinToInterrupt(sensorPin), increase, RISING);
  pinMode(switchPin, INPUT);
}


void loop() {
  volume = pulse * 0.000101112097171;
  delay(500);
  difference = FullTank  - volume;
  Serial.println(difference);
  seg.displayFloat(difference);
  delay(500);
  
  const bool switchState = digitalRead(switchPin);
  if (digitalRead(switchPin) == LOW) {
    delay(1000);
    seg.displayOn();
  } else {
    delay(1000);
    seg.displayOff();
  }

//  volume = pulse * 0.000101112097171;
//  delay(500);
//  difference = FullTank  - volume;
//  Serial.println(difference);
//  seg.displayFloat(difference);
//  delay(500);
}

void increase () {
  pulse++;
}

[J-M-L]

@K5BLZR

any other non-volatile memory suggestions

I2C FRAM ?

---

make that INPUT_PULLUP

@K5BLZR

  pinMode(switchPin, INPUT);

(using a button library would make it easier to deal with bouncing)

[Railroader]

You could use a button telling that power will be turned off. Then data are saved in EEPROM. At power up the EEPROM data are read and used.
Cutting off the display Vcc will cause ghost powering via the signal lines. The result is unpredictable.

[PaulRB]

@K5BLZR

void loop() {
  volume = pulse * 0.000101112097171;

You may need to protect against pulse getting updated half way through reading it in this line. Unless you are using an Arduino based on a 32-bit chip.

void loop() {
  unsigned long pulseNow;
  noInterrupts();
  pulseNow = pulse;
  interrupts();
  volume = pulseNow * 0.000101112097171;

[PaulRB]

@J-M-L

deal with bouncing

Why would bouncing be a problem?

[jim-p]

What does this do?
const bool switchState = digitalRead(switchPin);

[K5BLZR]

Thanks for the help, the UNO R3 does not come with an internal I2C FRAM right? What module and library would you recommend that would give me the most about of rewrite cycles? What library would you recommend for the button?
Thanks

[K5BLZR]

Could you type up some example code please, I've had difficulty understanding what is needed to get the EEPROM to read and write the "difference" value.

[J-M-L]

@PaulRB

Why would bouncing be a problem

In case OP wants less latency than waiting a full second every time the switch is tested

@K5BLZR

if (digitalRead(switchPin) == LOW) {
    delay(1000);
    seg.displayOn();
  } else {
    delay(1000);
    seg.displayOff();
  }

[alto777]

@Railroader

You could use a button telling that power will be turned off.

Yes.

Also, it's not terribly difficult to arrange it so the Arduino knows that power is soon to be lost, giving it enough time to throw some data into EEPROM.

FRAM is good, so it's down to what kind of fun you want to have.

I googled

 arduino write eeprom before loss of power

and suggest to you to do the same. Here's a thread that goes into some detail, see what you think:

Saving to EEPROM on power-out

Hi everybody, Is there a good strategy for saving a few key variables to EEPROM when you have a sudden power outage? Maybe a cap that can hold the board on long enough to get a few bytes written? I have a project that runs two metering pumps and keeps track of the liquid level in a few different containers. Whenever there is an interruption in power, the program can reset and take care of itself to get back into action, but it loses the values that hold the current liquid levels. I don't want …

and another

Need to save data to EEPROM on power off

Good afternoon, I am making a model of a dishwasher (using 12V components) using Arduino I have written all the code so far, but I am missing the save to eeprom function. Well, in reality it is already written, but it doesn't seem to work reliably I am powering everything off an LM7805 and I have connected a diode and bulk cap to the Arduino 5V supply like shown in the picture [immagine] I then read the Vcc using the secret voltmeter code. If this goes below 4 volts, I save to EEPROM and p…

The DS1307 is a lousy RTC, but it does make available battery backed RAM of a handful of bytes, totally available for any use you might find for them, yet another kind of fun…

HTH

a7

[J-M-L]

@K5BLZR

What module and library would you recommend that would give me the most about of rewrite cycles? What library would you recommend for the button?

The ones from my Adafruit link are good. (There are also other libraries out there like GitHub - RobTillaart/FRAM_I2C: Arduino library for I2C FRAM and you can get cheap modules from the fat east…)

But as explained above adding a capacitor and power sensing to your arduino is not very difficult so you could use also the EEPROM.

[jim-p]

So have you decided to use FRAM?