ADS1x15-ADC 1.2.0

Python library used for ADS1x15 analog to digital converter (ADC)

ADS1X15

Python library for I2C ADC ADS1015, ADS1115, and similar analog to digital converter. Works using I2C bus under Linux kernel.

Description

This library should work for the devices mentioned below, although not all sensors support all functionality.

Device	Channels	Resolution	Max sps	Comparator	ProgGainAMP	Notes
ADS1013	1	12	3300	N	N
ADS1014	1	12	3300	Y	Y
ADS1015	4	12	3300	Y	Y
ADS1113	1	16	860	N	N
ADS1114	1	16	860	Y	Y
ADS1115	4	16	860	Y	Y	Tested

As the 1015 and the 1115 are both 4 channels these are the most interesting from functionality point of view as these can also do differential measurement.

Initializing

The address of the ADS1113/4/5 is determined by to which pin the ADDR is connected to:

ADDR pin connected to	Address	Notes
GND	0x48	default
VDD	0x49
SDA	0x4A
SCL	0x4B

• ADS1x15() base constructor, should not be used.
• ADS1013(I2C_busId, I2C_address) Constructor with I2C bus id, and optional device address as parameter.
• ADS1014(I2C_busId, I2C_address) Constructor with I2C bus id, and optional device address as parameter.
• ADS1015(I2C_busId, I2C_address) Constructor with I2C bus id, and optional device address as parameter.
• ADS1113(I2C_busId, I2C_address) Constructor with I2C bus id, and optional device address as parameter.
• ADS1114(I2C_busId, I2C_address) Constructor with I2C bus id, and optional device address as parameter.
• ADS1115(I2C_busId, I2C_address) Constructor with I2C bus id, and optional device address as parameter.

import ADS1x15

# initialize ADS1115 on I2C bus 1 with default address 0x48
ADS = ADS1x15.ADS1115(1)

Configuration

Programmable Gain

• setGain(gain: int) set the gain value, indicating the maxVoltage that can be measured. Adjusting the gain allows one to make more precise measurements. Note: the gain is not set in the device until an explicit read/request of the ADC (any read call will do). See table below.
• getGain() returns the gain value (index).

PGA value	Max Voltage	Constant	Notes
0	±6.144V	PGA_6_144V	default
1	±4.096V	PGA_4_096V
2	±2.048V	PGA_2_048V
4	±1.024V	PGA_1_024V
8	±0.512V	PGA_0_512V
16	±0.256V	PGA_0_256V

• getMaxVoltage() returns the max voltage with the current gain.
• toVoltage(raw: int) converts a raw measurement to a voltage. Can be used for normal and differential measurements. The default value of 1 returns the conversion factor for any raw number.

The voltage factor can also be used to set HIGH and LOW threshold registers with a voltage in the comparator mode. Check the examples.

  f = ADS.toVoltage()
  ADS.setComparatorThresholdLow( 3.0 / f )
  ADS.setComparatorThresholdLow( 4.3 / f )

Operational mode

The ADS sensor can operate in single shot or continuous mode. Depending on how often one needs a conversion one can tune the mode.

• setMode(mode: int) 0 = MODE_CONTINUOUS, 1 = MODE_SINGLE (default) Note: the mode is not set in the device until an explicit read/request of the ADC (any read call will do).
• getMode() returns current mode 0 or 1, or INVALID_MODE = -1.

Data rate

• setDataRate(dataRate: int) Data rate depends on type of device. For all devices the index 0..7 can be used, see table below. Values above 7 ==> will be set to the default 4. Note: the data rate is not set in the device until an explicit read/request of the ADC (any read call will do).
• getDataRate() returns the current data rate (index).

The library has no means to convert this index to the actual numbers as that would take 32 bytes.

Data rate in samples per second, based on datasheet numbers.

data rate	ADS101x	ADS111x	Constant	Constant	Notes
0	128 SPS	8 SPS	DR_ADS101X_128	DR_ADS111X_8	slowest
1	250 SPS	16 SPS	DR_ADS101X_250	DR_ADS111X_16
2	490 SPS	32 SPS	DR_ADS101X_490	DR_ADS111X_32
3	920 SPS	64 SPS	DR_ADS101X_920	DR_ADS111X_64
4	1600 SPS	128 SPS	DR_ADS101X_1600	DR_ADS111X_128	default
5	2400 SPS	250 SPS	DR_ADS101X_2400	DR_ADS111X_250
6	3300 SPS	475 SPS	DR_ADS101X_3300	DR_ADS111X_475
7	3300 SPS	860 SPS	DR_ADS101X_3300	DR_ADS111X_860	fastest

ReadADC Single mode

Reading the ADC is very straightforward, the readADC() function handles all in one call. This function will wait until conversion finished.

• readADC(pin: int) normal ADC functionality, pin = 0..3. If the pin number is out of range, this function will return 0.

# read ADC in pin 0
ADS.readADC(0)

To read the ADC in an asynchronous way (e.g. to minimize blocking) one has to use three calls:

• requestADC(pin: int) Start the conversion. pin = 0..3.
• isBusy() (Is the conversion not ready yet?) or isReady() (Is the conversion ready?) Works only in SINGLE mode!
• getValue() Read the result of the conversion.

in terms of code

# configuration things here
ADS.setMode(ADS.MODE_SINGLE)    # SINGLE SHOT MODE
ADS.requestADC(0)               # request on pin 0

if ADS.isReady() :
    value = ADS.getValue()
    ADS.requestADC(0)           # request new conversion
# do other things here

See examples

ReadADC continuous mode

To use the continuous mode one need three calls

• setMode(0) 0 = MODE_CONTINUOUS, 1 = MODE_SINGLE (default). Note: the mode is not set in the device until an explicit read/request of the ADC (any read call will do).
• readADC(pin: int) or requestADC(pin: int) to get the continuous mode started.
• getValue() to return the last value read by the device. Note this can be a different pin, so be warned. Calling this over and over again can give the same value multiple times.

# configuration things here
ADS.setMode(ADS.MODE_CONTINUOUS)
ADS.requestADC(0)               # request on pin 0

while True :
    value = ADS.getValue()
    sleep(1)

By using isBusy() or isReady() one can wait until new data is available. Note this only works in the SINGLE_SHOT mode.

In continuous mode one should use the ALERT/RDY pin to trigger via hardware the readiness of the conversion. This can be done by using an interrupt.

See examples.

ReadADC Differential

For reading the ADC in a differential way there are 4 calls possible.

• readADC_Differential_0_1() returns the difference between 2 ADC pins.
• readADC_Differential_0_3() ADS1x15 only
• readADC_Differential_1_3() ADS1x15 only
• readADC_Differential_2_3() ADS1x15 only

# read differential ADC between pin 0 and 1
ADS.readADC_Differential_0_1(0)

The differential reading of the ADC can also be done with asynchronous calls.

• requestADC_Differential_0_1() starts conversion for differential reading
• requestADC_Differential_0_3() ADS1x15 only
• requestADC_Differential_1_3() ADS1x15 only
• requestADC_Differential_2_3() ADS1x15 only

After one of these calls one need to call

• getValue() Read the result of the last conversion.

The readiness of a CONTINUOUS conversion can only be detected by the RDY line. Best to use an interrupt for this, see examples.

Threshold registers ==> mode RDY pin

If the thresholdHigh is set to 0x0100 and the thresholdLow to 0x0000 the ALERT/RDY pin is triggered when a conversion is ready.

• setComparatorThresholdLow(lo) writes value to device directly.
• setComparatorThresholdHigh(hi) writes value to device directly.
• getComparatorThresholdLow() reads value from device.
• getComparatorThresholdHigh() reads value from device.

See examples.

Comparator

Please read Page 15 of the datasheet as the behaviour of the comparator is not trivial.

NOTE: all comparator settings are copied to the device only after an explicit readADC() or requestADC()

Comparator Mode

When configured as a TRADITIONAL comparator, the ALERT/RDY pin asserts (active low by default) when conversion data exceed the limit set in the high threshold register. The comparator then de-asserts when the input signal falls below the low threshold register value.

• setComparatorMode(mode: int) value 0 = TRADITIONAL 1 = WINDOW,
• getComparatorMode() returns value set.

If the comparator LATCH is set, the ALERT/RDY pin asserts and it will be reset after reading the sensor (conversion register) again. An SMB alert command (00011001) on the I2C bus will also reset the alert state. Not implemented in the library (yet)

In WINDOW comparator mode, the ALERT/RDY pin asserts if conversion data exceeds the high threshold register or falls below the low threshold register. In this mode the alert is held if the LATCH is set. This is similar as above.

Polarity

Default state of the ALERT/RDY pin is LOW, can be to set HIGH.

• setComparatorPolarity(pol) Flag is only explicitly set after a readADC() or a requestADC()
• getComparatorPolarity() returns value set.

Latch

Holds the ALERT/RDY to HIGH (or LOW depending on polarity) after triggered even if actual value has been 'restored to normal' value.

• setComparatorLatch(latch: int) 0 = NO LATCH, not 0 = LATCH
• getComparatorLatch() returns value set.

QueConvert

Set the number of conversions before trigger activates. The setComparatorQueConvert(mode: int) is used to set the number of conversions that exceed the threshold before the ALERT/RDY pin is set HIGH. A value of 3 (or above) effectively disables the comparator. See table below.

• setComparatorQueConvert(mode: int) See table below.
• getComparatorQueConvert() returns value set.

Value	Constant	Meaning	Notes
0	COMP_QUE_1_CONV	trigger alert after 1 conversion
1	COMP_QUE_2_CONV	trigger alert after 2 conversions
2	COMP_QUE_4_CONV	trigger alert after 4 conversions
3	COMP_QUE_NONE	Disable comparator	default

Threshold registers comparator mode

Depending on the comparator mode TRADITIONAL or WINDOW the thresholds registers mean something different see - Comparator Mode above or datasheet.

• setComparatorThresholdLow(lo) set the low threshold; take care the hi >= lo.
• setComparatorThresholdHigh(hi) set the high threshold; take care the hi >= lo.
• getComparatorThresholdLow() reads value from device.
• getComparatorThresholdHigh() reads value from device.

Future ideas & improvements

• Improve documentation
• More examples ?
• SMB alert command (00011001) on I2C bus?

Examples

See examples in this link