PASC

The precision analog to serial converter (PASC) is an optional data acquisition (DAQ) device. PASC is only required to log data from instruments communicating through analog channels. PASC can be built with an Arduino Uno type microcontroller and a precision analog to digital converter such as the Texas Instrument ADS1015 or ADS1115 developpement boards. The wiring instructions to build your own are available at Adafruit website.

We uploaded the firmware to the microcontroller following these instructions.

  1. Load mcu_firmwares/PASC.cpp in the Arduino IDE:

    1. In ~/Documents/Arduino create a folder PASC/
    2. Copy and rename mcu_firmware/PASC.cpp to ~/Documents/Arduino/PASC/PASC.ino
    3. Load PASC.ino from Arduino Software (File > Open…)

  2. Comment/uncomment appropriate lines in PASC.ino following instructions in comments of the file.

  3. Compile and upload PASC to the microcontroller (button on the top left of Arduino IDE).

PASC Precision and Accuracy Validation

The precision and accuracy of the PASC serial number 001 and 002 were assessed with a Fluke 85 III Voltmeter. We found no significant bias and a reasonable root mean square error of (5.3 mV), the data is presented in the Figure below.

_images/pasc_validation.png

Configuration in previous versions of Inlinino

The parameters required to setup the PASC with the previous version of Inlinino are:

  • module
  • name
  • frequency
  • gain (for ADS1X15 only)
  • variables
    • pin
    • units
frequency: < int >

Frequency (in Hertz) at which the Arduino will be reading and reporting voltage.

Note

Theoretical maximum sampling frequency are:

Uno ADS-1015 ADS-1115
9600 3300 860

Maximum frequency taking into account conversion delay:

Number Uno ADS-1015 ADS-1115
of PIN SE SE DIF SE DIF
1 50 1000 500 125 62
2 25 500 250 62 31
3 16 333
41
4 12 250
31
5 10
[1]SE: Single ended connection
[2]DIF: Differential connection
gain: < int >

Available only for the ADS1X15 interface.

Set gain of ADS-1x15.

The ADC input range (or gain) can be changed via this parameter.

Available options are:

Gain VDD Resolution (1 bit = x mV)
x (+/- V) Uno ADS-1015 ADS-1115
2/3 6.144
3 0.1875
5.0 4.88
1 4.096
2 0.125
2 2.048
1 0.0625
4 1.024
0.5 0.03125
8 0.512
0.25 0.015625
16 0.256
0.125 0.0078125

Note

A gain of two third is set with "gain":23.

Warning

Never exceed the VDD +0.3V ! Exceeding the upper or lower limits may damage a channel of your ADC or destroy it ! Be carefull with this setting, be conservative and start with a gain of 2/3 ("gain":23) for an input of +/- 6.144 V

Note

Gain is displayed on the digital display on the top left of the GUI. Gain setting is recorded in the output log file with the units.

variables: {}

Each pin connected to the board need to be declared in this section. Each variable has a name, a pin name and units.

pin: "< string >"

Set which pin to read measurments from.

pin single ended options are:

  • SIN_A0
  • SIN_A1
  • SIN_A2
  • SIN_A3
  • SIN_A4
  • SIN_A5 (available only on Arduino Uno)

pin differential connections options are (available only on ADS-1X15):

  • DIF_A01
  • DIF_A23

Example of configuration for logging data of an analog fluorometer, the WET Labs WSCD. The instrument output is 12 bit 0-5 Volts, as we are taking measurements in very clear water, signal should never go above 3 Volts. In order to match the resolution of the instrument, an ADS-1015 is used with a gain setting of 1x and a frequency of 1 Hz (as the instrument operates at 1 Hz). The <user_cfg.json> file look like:

"instruments":{
  "WSCD_859":{
    "module":"Arduino",
    "name":"ADS1015",
    "frequency":1,
    "gain":1,
    "variables":{
      "fdom":{
        "pin":"SIN_A0",
        "units":"counts"
      }
    }
  }
}