AHMERIXIS MD - Making my Own Design Detector

[nncu2020]

Not happy with my results today

Attached the results I achieved today... the best sample time was about 7.9 uS with 8 bit... until about 10Khz (signal) the resolution is acceptable... but something over that value is not good.

I am using an Arduino Nano.


long numSamples = 0;
byte samples = 200;
byte values[200];
int i;
long t, t0;


void setup()
{
Serial.begin(9600);


ADCSRA = 0; // clear ADCSRA register
ADCSRB = 0; // clear ADCSRB register
ADMUX |= (0 & 0x07); // set A0 analog input pin
ADMUX |= (1 << REFS1) | (1 << REFS0); // set reference voltage
ADMUX |= (1 << ADLAR); // left align ADC value to 8 bits from ADCH register


// sampling rate is [ADC clock] / [prescaler] / [conversion clock cycles]
// for Arduino Uno ADC clock is 16 MHz and a conversion takes 13 clock cycles
//ADCSRA |= (1 << ADPS2) | (1 << ADPS0); // 32 prescaler for 38.5 KHz
//ADCSRA |= (1 << ADPS2); // 16 prescaler for 76.9 KHz
ADCSRA |= (1 << ADPS1) | (1 << ADPS0); // 8 prescaler for 153.8 KHz
//ADCSRA |= (1 << ADPS1); // 4 prescaler
//ADCSRA |= (1 << ADPS0); // 4 prescaler


ADCSRA |= (1 << ADATE); // enable auto trigger
ADCSRA |= (1 << ADIE); // enable interrupts when measurement complete
ADCSRA |= (1 << ADEN); // enable ADC
ADCSRA |= (1 << ADSC); // start ADC measurements
}


ISR(ADC_vect)
{
if (numSamples < samples){
//byte x = ADCH; // read 8 bit value from ADC
values[numSamples] = ADCH;
//Serial.println(x);
numSamples++;
}
}

void loop()
{

if (numSamples == samples)
{
Serial.println("---- begin");
t = micros() - t0; // calculate elapsed time


Serial.print("uS between samples: ");
Serial.println((t * 1.0) / (samples * 1.0));
Serial.println(t);
//delay(2000);


for(i = 0; i < samples; i++) {
//Serial.println(values[i]);
Serial.println(values[i] * 1.1 / 255.0);
}
delay(10000);

// restart
t0 = micros();
numSamples = 0;
}
}

[waltr]

hint:
when posting code to the forum put 'code' tags around the code to post.

The code tags are [ c o d e ] 'code to post' [ / c o d e ]
remove the spaces inside the square brackets like this and all the formatting, indents, etc. are not removed.

long numSamples = 0;
byte samples = 200; 
byte values[200];
int i;
long t, t0;


void setup()
{
  Serial.begin(9600);
  
  
  ADCSRA = 0;             // clear ADCSRA register
  ADCSRB = 0;             // clear ADCSRB register
  ADMUX |= (0 & 0x07);    // set A0 analog input pin
  ADMUX |= (1 << REFS1) | (1 << REFS0);  // set reference voltage
  ADMUX |= (1 << ADLAR);  // left align ADC value to 8 bits from ADCH register


  // sampling rate is [ADC clock] / [prescaler] / [conversion clock cycles]
  // for Arduino Uno ADC clock is 16 MHz and a conversion takes 13 clock cycles
  //ADCSRA |= (1 << ADPS2) | (1 << ADPS0);    // 32 prescaler for 38.5 KHz
  //ADCSRA |= (1 << ADPS2);                     // 16 prescaler for 76.9 KHz
  ADCSRA |= (1 << ADPS1) | (1 << ADPS0);    // 8 prescaler for 153.8 KHz
  //ADCSRA |= (1 << ADPS1);    // 4 prescaler 
  //ADCSRA |= (1 << ADPS0);    // 4 prescaler


  ADCSRA |= (1 << ADATE); // enable auto trigger
  ADCSRA |= (1 << ADIE);  // enable interrupts when measurement complete
  ADCSRA |= (1 << ADEN);  // enable ADC
  ADCSRA |= (1 << ADSC);  // start ADC measurements
}


ISR(ADC_vect)
{
  if (numSamples < samples){
    //byte x = ADCH;  // read 8 bit value from ADC
    values[numSamples] = ADCH;
    //Serial.println(x);
    numSamples++;
  } 
}
  
void loop()
{
  
  if (numSamples == samples)
  {
    Serial.println("---- begin");
    t = micros() - t0;  // calculate elapsed time


    Serial.print("uS between samples: ");
    Serial.println((t * 1.0) / (samples * 1.0));
    Serial.println(t);
    //delay(2000);


    for(i = 0; i < samples; i++) {
        //Serial.println(values[i]);
        Serial.println(values[i] * 1.1 / 255.0);
    }
    delay(10000);
    
    // restart
    t0 = micros();
    numSamples = 0;
  }
}

[nncu2020]

hint:
when posting code to the forum put 'code' tags around the code to post.

The code tags are [ c o d e ] 'code to post' [ / c o d e ]
remove the spaces inside the square brackets like this a...........

Great, I will next time!

Thanks

[nncu2020]

Fake LF357 vs TL071?

Hi everyone,

Which one you think looks better... I have replaced the LF357 (which I think it is fake) with a TL071.

Which one you think work better, see the attached picture.

Thanks a lot!

[green]

Hi everyone,

Which one you think looks better... I have replaced the LF357 (which I think it is fake) with a TL071.

Which one you think work better, see the attached picture.

Thanks a lot!
[ATTACH]53323[/ATTACH]

I like the 357 trace better. Looks like could sample either after a 12us delay so maybe not much difference unless one has more noise for low signal targets.

[nncu2020]

Hi Green,

Why do you think LF357 is better?

TL071 has a more smooth curve when no object is present. I see a best balance ground-vcc/gnd-vee in TL071.

Can you please give more details? I am just beginning :-)

I bought the LF357 from China (ebay), so I don't think it is really a real one.

[green]

Hi Green,

Why do you think LF357 is better?

TL071 has a more smooth curve when no object is present. I see a best balance ground-vcc/gnd-vee in TL071.

Can you please give more details? I am just beginning :-)

I bought the LF357 from China (ebay), so I don't think it is really a real one.

357 is faster, gets to zero sooner. Don't know if it matters if both are out of saturation when sample is taken. I'm still learning also, maybe someone else could give their thoughts.

[nncu2020]

Maybe I can use the null offset pins to balance the output .... ?

[green]

Maybe I can use the null offset pins to balance the output .... ?

Why do you need to balance the output? Aren't you reading the output with an A-D?

[nncu2020]

No, I just want to know why LF357 and TL071 have different behavior if the circuit is exactly the same.

I will try to use an ADC, but not in that specific point. I will use a voltage range coupling to input the signal to the ADC.

[green]

No, I just want to know why LF357 and TL071 have different behavior if the circuit is exactly the same.

I will try to use an ADC, but not in that specific point. I will use a voltage range coupling to input the signal to the ADC.

________ TL071 LF357
bandwidth 3MHz 20MHz
slew rate 13V/us 50V/us

[flex]

LF357 has 50V/us slew rate compared to 13V/us of TL071 . This is a main reason. If LF doesn't work very stable try to put capacitor in negative feedback, or try to find original LF not from china . There are lot of ebay sellers who sell old (1980 YOM) LF