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16  International / Hardware / Re: Amperometro con Sensore ACS758 on: December 06, 2012, 07:56:26 am
per quanto riguarda il settaggio di sensitività avete riscontrato i miei stessi problemi? (vedi post sopra)
tks
17  Using Arduino / General Electronics / Re: ac current meter using acs758 hall sensor on: November 22, 2012, 09:30:15 am
i've made further test
it seems that with a sensitivity of 0.034/2 it works from 4A to 12A quite well.
0.034 seems ok, because my supply is 4.7V, sensitivity should be 0.03824 +- 5mV (Electrical offset voltage from datasheet)
but i've to use half of it.

p.s checked also my multimeter and it has no problem.

have you  any suggestion, or anyone here that can test my code on other chip?

tks!
18  International / Hardware / Re: Amperometro con Sensore ACS758 on: November 21, 2012, 04:56:20 am
ciao,
se qualcuno fosse interessato, ne parlo in questo post, abbiamo "quasi" risolto, ci sono dei problemi con il settaggio della sensitività
http://arduino.cc/forum/index.php/topic,133144.0.html
19  International / Generale / Re: Presentazioni nuovi iscritti, fatevi conoscere da tutti! on: November 20, 2012, 09:03:16 am
ciao a tutti, sono un informatico, appassionato da qualche anno di elettronica... per questo mi ritrovo spesso su questo forum.  smiley-grin
20  Using Arduino / General Electronics / Re: ac current meter using acs758 hall sensor on: November 20, 2012, 06:34:56 am
to me seems allegro official, but may not be.
see attached pic
21  Using Arduino / General Electronics / Re: ac current meter using acs758 hall sensor on: November 20, 2012, 06:04:08 am
Did you get it from a reputable supplier?

Absolutely not  smiley-eek ebay seller from china smiley did you think it is a fake or wrong printed chip?
22  Using Arduino / General Electronics / Re: ac current meter using acs758 hall sensor on: November 20, 2012, 05:49:28 am
yes, printed on chip.

i change the ratiometric change in sesitivity derived from my voltage (page 16 acs758 datasheet)
SENSnew = (Vin / 5v) SENSdatasheet
my board supply is 4.70V so the sensitivity should be 37.6mV, next 0.036 / 2 = 0.018.. ?


23  Using Arduino / General Electronics / Re: ac current meter using acs758 hall sensor on: November 20, 2012, 05:20:48 am
damned paranthesis! smiley

later i will use #define or const for my code, code here is only for test purpose

my new code has a simple filter for adc to remove offset

Code:
uint16_t i = 0;
int16_t adc_raw = 0;
int16_t adc_rawlast = 0;
int16_t adc_filtered = 0;
int16_t adc_lastfiltered = 0;
for(i=0; i<100; i++) {
  adc_rawlast = adc_raw;
  adc_raw = (512 - adc_read(2));
  adc_lastfiltered = adc_filtered;
  //digital high pass filters to remove offset.
  adc_filtered = 0.996*(adc_lastfiltered+adc_raw-adc_rawlast);
  s = adc_filtered * adc_filtered;
  ssum += s;
  _delay_us(100);
}
d = sqrt(ssum/100) * 5 / (0.018 * 1024.0);
ssum = 0;

now with a sensitivity of 0.018 (0.036 (close to 0.04) /2) things seems right from 0.5A to 12A
my chip is ACS758 LCB-050B

because
d = sqrt(ssum/100) * 5 / (0.018 * 1024.0);
is like
d = 2 * sqrt(ssum/100) * 5 / (0.036 * 1024.0);

isn't that there is a 2 multiply left?

24  Using Arduino / General Electronics / Re: ac current meter using acs758 hall sensor on: November 20, 2012, 04:16:30 am
1. In the plot you provided in reply #9, at the 6.4A setting, what are the ADC readings at the high and low peaks?

2. How do you know that the current is 6.4A?

1. @6.54A 547max 480min (it's 6.54A sorry)
   + @3.65A > 547max 512min
2. multimeter (not true RMS)
25  Using Arduino / General Electronics / Re: ac current meter using acs758 hall sensor on: November 20, 2012, 03:48:12 am
it's a 1500w hair dryer with three position (stop, 3.4A, 6.4A, as read by my multimeter, which is not true rms).
i've also try attaching another heater, from 6.4A the current sucked it sine wave form BUT, and the extimated current measure is right IF i change the sensitivity A LOT.

Code:
uint16_t i = 0;
  double sensitivity = 0.0016;
  int16_t adc_raw = 0;
  int16_t adc_zero = 512; //as read when there is no current on the load
  for(i=0; i<100; i++) {
    adc_raw = adc_read(2);
    l += (adc_raw - adc_zero)*(adc_raw - adc_zero);
    _delay_us(100);
  }
  d = (sqrt(l)/100) * 5 / (0.0016 * 1024.0) - 0.5;
  l = 0;

Code:
d = (sqrt(l)/100) * 5 / (0.0016 * 1024.0) - 0.5;

with sensitivity of 0.0016 and an offset of 0.5 i've almost right result on 0A and above 3.4A (tried only 6.4A / 8A / 12A)
but from datasheet sensitivity is 0.04 ( = 25 * 0.0016)
26  Using Arduino / General Electronics / Re: ac current meter using acs758 hall sensor on: November 19, 2012, 02:08:55 pm
Code:
    l += pow(adc_raw - adc_zero, 2);
You don't want to use pow() here, it uses float, double and is far too slow (it does logarithms, antilogarithms).

Code:
    long val = adc_raw - adc_zero ;
    l += val * val ;

You need to be sampling the waveform at 1000Hz or more for good accuracy so its important
the maths isn't too slow.  Lose the delays - if you want to control the timing you should use millis() or
micros() so you can synchronize to a multiple of 50 or 60Hz.


First look at a set of raw values from the sensor to check they are what you'd expect (sample a
bunch into an array, then print out the array, printing out is too slow also).  You should see a
clear sinusoidal pattern with the correct amplitude.

Then test your calculation code with known correct raw values to see if the arithmetic is correct.

attached a plot of raw values, just analogRead of the pin.
it has a strange behavior
+ the first part (y=512) is a line, device is power off.
+ the second part, some sort of 1/2 sine wave, only + part is present, device @ 3.4Amp, [strange here, why??]
+ the third part is a sine wave, device @ 6.4Amp

sensor has the same circuit as the datasheet propose, it does not change if Cf and / or Rf are present or not.
27  Using Arduino / General Electronics / Re: ac current meter using acs758 hall sensor on: November 19, 2012, 11:11:57 am
Almost. You need to convert (adc_raw - adc_zero) to type 'long' before you square it, because the square may exceed the range of an int. You will need to declare currentac with type 'long' too. After taking the sqrt, you need to adjust it for the sensitivity etc. just as you do for DC.

i've left all untyped i know smiley-wink
typed code is below.


i've tried two ways, but it doesn't seams to works.

test 1------------------
subtract the zero-current value (512 or thereabouts) from the raw readings, square that, and add it to an accumulator variable. When you have accumulated enough samples, take the square root if the accumulator and divide by the number of readings.

Code:
double d = 0; long l = 0;
for(;;) {
  uint16_t i = 0;
  int16_t adc_raw = 0;
  int16_t adc_zero = 512;
  for(i=0; i<100; i++) {
    adc_raw = adc_read(2);
    l += pow(adc_raw - adc_zero, 2);
    _delay_us(100);
  }
  d = (sqrt(l)/100) * 5 / (0.04 * 1024.0);
  l = 0;


test 2------------------
average the square of the current, and take the square root of the average

Code:
double c = 0, d = 0;
for(;;) {
  uint16_t i = 0;
  int16_t adc_raw = 0;
  int16_t adc_zero = 512;
  for(i=0; i<100; i++) {
    adc_raw = adc_read(2);
    adc_raw = adc_raw - adc_zero;
    c += pow(adc_raw * 5 / (0.04 * 1024.0), 2);
    _delay_us(100);
  }
  d = sqrt(c)/100;
  c = 0;
 
  ... print c...
}



i'm testing a 6.4 Amp 220V 50hz device
both code i obtain almost the same value, which is 0.27Amp, but is not correct smiley-sad
28  Using Arduino / General Electronics / Re: ac current meter using acs758 hall sensor on: November 19, 2012, 09:49:03 am
The max value you can read is indeed 1023, but the correct value to use in the calulation is 1024. See section 24.7 of the atmega328p datasheet.
Thank you for this info!

Are you trying to measure alternating current? If so, you need to average the square of the current, and take the square root of the average (that's what RMS means). Easiest way is to subtract the zero-current value (512 or thereabouts) from the raw readings, square that, and add it to an accumulator variable. When you have accumulated enough samples, take the square root if the accumulator and divide by the number of readings.
Yes ac current.

so,
for AC current something like this
Code:
samplesnum = 100;
adc_zero = 512; //as read when there is no current on the load
sensitivity = 0.04; //as read from datasheet
for(i=0; i<samplesnum ; i++)
  adc_raw = analogRead(1);
  currentacc += (adc_raw - adc_zero) * (adc_raw - adc_zero); //subtract the zero-current value (512 or thereabouts) from the raw readings, square that, and add it to an accumulator variable
}
currentac = sqrt(currentacc)/samplesnum; //take the square root if the accumulator and divide by the number of readings.

for DC current something like this
Code:
adc_zero = 512; //as read when there is no current on the load
sensitivity = 0.04; //as read from datasheet
currentdc = (adc_raw - adc_zero) * 5/(sensitivity * 1024)

right?
29  Using Arduino / General Electronics / Re: ac current meter using acs758 hall sensor on: November 19, 2012, 08:55:09 am
thank you for reply

The value adcdiv in your calculation should be 1024, not 1023
reason for 1024, correct me if i'm wrong
adcraw is a 10bit values, so from 0(min) to 1023(max = 2^10-1), so the max values here is 1023

A value of 512 with no current flowing is exactly right, however the device may have an offset of a few mV, so the value may be a few counts out. Noise on the +5V line will affect the reading.
which is the math to use for transform adc values to amepere using an acs758.

i get adc samples for adc current making an avarage of "many" values, i.e. at least 2 times the period of my 50Hz primary current, and my adc values are stable.
but maybe my formula is not correct, i'm using this one:
amp = (adcraw*adcvref/adcdiv- adcvref/2) / sensitivity;

because with "small" adcraw changes i have "big" change in amp
es.
(  512  *5/1023 - 5/2)/0.04 = 0.062   
(  516  *5/1023 - 5/2)/0.04 = 0.54    (1/2Amp!)
and also consider the max raw value of 1023
(  1023  *5/1023 - 5/2)/0.04 = 62.5
acs758-050b is rated as 50Amp max, the max raw value i should read is almost 900
30  Using Arduino / General Electronics / ac current meter using acs758 hall sensor on: November 19, 2012, 07:14:52 am
hello,

i'm trying to read ac current using a bidirection allegro hall sensor acs758-050b
i've a problem using it.
when i do not connect anything to this sensor i read
* a raw value of 516 with a input voltage of 4.80V +-0.05V
* a raw value of 512 with a input voltage of 4.70V +-0.05V

to convert the value to current i use the current formula
adcvref = 5
adcdiv = 1023
sensitivity = 0.04 ( acs758-050b sensitivity datasheet)
amp = (adcraw*adcvref/adcdiv- adcvref/2) / sensitivity;

anyway the problem with the raw value persist, even if i change the reference (adcvref) current value to real adcvalue (4.80 or 4.70)

can anyone help me?
thanks!
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