ADS1115 Breakout not working

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strakat
 
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ADS1115 Breakout not working

Post by strakat »

Hi folks!

I just got my new ADS1115 board soldered and connected to my Arduino Nano for a test setup.

I used a test sketch from the Library examples to check the Wire communication.

BOING!
I CANT RUN THAT THING!

As soon as a readADC function is called the sketch hangs and the arduino resets.

I only wired the GND, VCC, SCL and SDA Lines, so NOTHING is or was attached to the inputs.
I just wanted to check if it communicates.

GND and Vcc go to the corresponding pins on the Nano and SCL Goes to Analog5, SDA to Analog4 as the Pinout says.

So i wondered what was wrong and got my scope running.

If i disconnect SCL and SDA i can see the clock signal on the Analog 5 pin.

BUT:

As soon as i connect SCL and SDA to the ADC the voltage on the Pins A4 and A5 break down to about 300mv and the Nano resets!

WHAT THE HELL IS THAT?

So i measured the resistance on the GND and SDA / SCL Pins on the breakout to find out there is
a resistance of about 500kOhms between GND and SCL but only 300ohms (jYes 300 Ohms NOT kOhms)
resistance between GND and SDA Line. (seems to me like a schort circuit) with nothing connected to the board at all.
Is this normal?

Am i wiring something wrong or may the ADC Board be faulty?
Attached is an image of my setup.
ADS1115.jpg
ADS1115.jpg (224.1 KiB) Viewed 926 times
Any help greatly appreciated.

Thanks,
Christian

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adafruit_support_rick
 
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Re: ADS1115 Breakout not working

Post by adafruit_support_rick »

Please email [email protected] with a link to this thread for a replacement ADS1115

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KYR
 
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Re: ADS1115 Breakout not working

Post by KYR »

Hi all,

I would like to ask, what is the stability and accuracy of the internal voltage reference. this is not mentioned in the datasheet and is of crucial importance when measuring analog voltages

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adafruit_support_rick
 
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Re: ADS1115 Breakout not working

Post by adafruit_support_rick »

Figure 19 on page 8 in the datasheet gives the total error expected.

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KYR
 
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Re: ADS1115 Breakout not working

Post by KYR »

Thank you for your prompt reply. I have another one question with respect the use of the amplifier. Looking at the examples, I derive that I cannot input a 0-5V analog signal with a x16gain. Is that correct? For using the 16x gain, input signal should be +/- 0.256V (?). Do you know the total error for that FS?

From figure 19, I understand that the worst case error is 3mV, while 1bit is 1mV resolution (for 2,048voltage) . From that I can understand that the full resolution cannot be achieved. Please correct me if I am wrong, I am trying to understand, what will be the exact resolution at the end.

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Re: ADS1115 Breakout not working

Post by adafruit_support_rick »

KYR wrote:I derive that I cannot input a 0-5V analog signal with a x16gain. Is that correct? For using the 16x gain, input signal should be +/- 0.256V (?).
Correct
KYR wrote:Do you know the total error for that FS?
No.
KYR wrote:From figure 19, I understand that the worst case error is 3mV, while 1bit is 1mV resolution (for 2,048voltage) . From that I can understand that the full resolution cannot be achieved. Please correct me if I am wrong, I am trying to understand, what will be the exact resolution at the end.
Interesting. I'm wondering if the vertical axis in Fig 19 is mislabeled. All the other error charts are labeled in uV. I don't see how they could add up to >3mV.

We have the latest version of the datasheet posted. You might find more information on this page:
http://www.ti.com/product/ADS1115/technicaldocuments

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adafruit_support_mike
 
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Re: ADS1115 Breakout not working

Post by adafruit_support_mike »

Minor correction: Your input signals can't go beyond the AD1115's supply rails.

A +/-1v differential signal involves two signals, both of which change, but which remain within 1v of each other.

- When A=1v and B=0v, you have a differential voltage of 1v (A is 1v more positive than B)

- When A=0v and B=1v, you have a differential voltage of -1v (A is 1v more negative than B)

- When A=5v and B=4v, you have a differential voltage of 1v again.

In that last example, both A and B share 4v of 'common mode' voltage which falls away when you take a differential measurement.

Differential measurements are useful when you have signals that are combined with noise that appears on both inputs (the output from lots of sensors behaves that way). The common-mode noise falls away and you're left with just the difference between the two inputs.

Both inputs have to remain between the VCC and GND voltages for the ADC though.

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