Digital Voltmeter (0-99%)

[rascupanamuha]

I want to make voltmeter using arduino uno and 2x 7seg display
My battery has around 9V when it is empty, and that should be 00 on display,
and 12.6V when it is full, and that should be 99 on display.
What is the easiest way to do that?

 

[Ian Rogers]

Simple mapping... I think there is a function built in to map function 9.00 - 12.60 to 0 - 99...


Also there is 7 segment tutorials here.. https://tronixstuff.wordpress.com/tutorials/

 

[rascupanamuha]

Yep thats it !
This is my first project with arduino, so i am learning analog inputs, digital outputs, etc

 

[be80be]

Use map

Description
Re-maps a number from one range to another. That is, a value of fromLow would get mapped to toLow, a value of fromHigh to toHigh, values in-between to values in-between, etc.
Does not constrain values to within the range, because out-of-range values are sometimes intended and useful. The constrain() function may be used either before or after this function, if limits to the ranges are desired.
Note that the "lower bounds" of either range may be larger or smaller than the "upper bounds" so the map() function may be used to reverse a range of numbers, for example
y = map(x, 1, 50, 50, 1);
The function also handles negative numbers well, so that this example
y = map(x, 1, 50, 50, -100);
is also valid and works well.

Like this

Example
/* Map an analog value  (0 to 99) from 9 volts to 12.6 */
void setup() {}

void loop()
{
  int val = analogRead(0);
  val = map(val, 730, 1023, 0, 99);
  Serial.write(val);
}

should output 0 to 99 for a close 9 to 12.6 volts This outputs to the com port

 

[rascupanamuha]

Thank you !
I tried to do this with 9V battery which is 9.6V full and 5.4V empty. I am not sure about that but nevermind for now

Problem is that i have "ghost" effect on my 2 numbers and i cant figure out why. I have 2x 7 segment displays that should show 99 at 9.6V, and 0 at 5.4V
Also i use voltage divider, so my actual input voltages are 2.7 to 4.8V
Can you please help me what to change to have clear numbers? (i use 74hc595 shiftregisters)

void loop() {
  
  int val = analogRead(5);
  val = map(val, 550, 982, 0, 99);
  first = val/10;
  second = val%10;
   
  digitalWrite(seg1, LOW); digitalWrite(seg2, HIGH);
  digitalWrite(latchpin, LOW);
  shiftOut(datapin, clockpin, MSBFIRST,br(first)); 
  digitalWrite(latchpin, HIGH);
  delay (10); digitalWrite(seg1, HIGH); digitalWrite(seg2, HIGH);
  
  digitalWrite(seg1, HIGH); digitalWrite(seg2, LOW);
  digitalWrite(latchpin, LOW);
  shiftOut(datapin, clockpin, MSBFIRST,br(second));
  digitalWrite(latchpin, HIGH);
  delay (10); digitalWrite(seg2, HIGH); digitalWrite(seg1, HIGH);

And aditional question, how can i "take" analogRead(5) not every ms or even faster but for example every 1000ms? If i put after that delay(1000); it takes it every 1sec, but also slowes down whole program

 

[be80be]

You can use a millis and and just check it for 1000 ms roll overs. Ad to stop ghosting turn on the seven segment after the write to it new data out set shiftreg light digits data change digits off load new data digit on.

 

[rascupanamuha]

Can you please explain me a little bit easier? I am not best in programming and because of that i dont understand that easy
Can you add that peace of code please?

 

[be80be]

Have a read over here https://www.arduino.cc/en/Tutorial/BlinkWithoutDelay It shows you all about how that millis works

 

[rascupanamuha]

Okay, i will try that tomorow, but can you also give me a link or something about ghosting in my case?

 

[be80be]

The ghosting is because your not blanking the display. See you write to the shiftreg then turn on the display. Your code has them on when you do a update.

Like this

digitalWrite (seg1, low); digitalWrite(seg2,low):
shiftOut //data here
digitalWrite (segX,High); //desplay your data here
digitalWrite (seg1, low); digitalWrite(seg2,low)://turn them off to load new data
shiftOut // new data here
digitalWrite (segX,High);//desplay your data here

 

[rascupanamuha]

The ghosting is because your not blanking the display. See you write to the shiftreg then turn on the display. Your code has them on when you do a update.

Like this

digitalWrite (seg1, low); digitalWrite(seg2,low):
shiftOut //data here
digitalWrite (segX,High); //desplay your data here
digitalWrite (seg1, low); digitalWrite(seg2,low)://turn them off to load new data
shiftOut // new data here
digitalWrite (segX,High);//desplay your data here

About ghosting you were absolutely right
I have corrected it now, and it is good now. Ill try to slow down refresh rate now, then it will be finished project

Everything works perfectly now, thanks to you !
Ill post some pictures or videos as soon as i solder this together (it is all on breadbord for now)

 

[rascupanamuha]

I have solder it together and something really wierd is happening

The same 75hc595 on breadbord IS working well and on my soldered board isnt :S

I have checked pins, and pin 8 and 10 are connected to ground and pins 13 and 16 are connected to +5V. Input pins are connected like on breadbord and on all otput pins is 0V, when on pin 6 should be +5V (and it is, on the same chip on the breadbord). So what can be wrong with this?

 

[be80be]

Post a sch and a good picture. And did you put a .01 uf cap on the power pin.
But most likely a bad solder joint.

 

[rascupanamuha]

No i didnt put it. But on my breadbord version it is working. I dont have a scheme, but i can explain it to you, it is easy

I have common catode led display (2 of them with 2 digits ,4 digits all together). Segment pins of them are connected through 1k resistors to outputs of first 74hc595. Outputs of second 74hc595 are connected to 4 "grounds" of displays which when are LOW are active, and that digit shows..
So the difrent from the breadbord version is that here i have 2x 74hc595, and 3 output pins from arduino and on breadbord i have 5 outputs from arduino. Ill post a picture but it is really messed up

 

[rascupanamuha]

I think i have figured it out
Maybe i put 10 on groud and 13 to +5. That should be vice versa