Grove - I2C ADC
Introduction
3.3V 5.0V I2C
Grove - I2C ADC is a 12-bit precision ADC module based on ADC121C021. It helps
you increase the accuracy of value collected from analog sensor by providing a
constant reference voltage. Because its address is changeable, you can use up to 9
I2C ADC at the same time at most. At the other hand, this module provides auto
sleep function which lowers the power consumption considerably.
Features
• Low power cons umptio n
• High precision
• Automatic power-down mode
• Address changeable
Tip
More details about Grove modules please refer to Grove System
Specifications
Item
Typical
Unit
Working Voltage
5.0
VDC
Resolution
12
Bit
Sample Rate
188.9
ksps
Dimension
40X20
mm
Raspberry
Pi
LinkIt
ONE
Platforms Supported
Arduino Wio BeagleBone
Caution
The platforms mentioned above as supported is/are an indication of the module's hardware or theoritical compatibility. We only
provide software library or code examples for Arduino platform in most cases. It is not possible to provide software library /
demo code for all possible MCU platforms. Hence, users have to write their own software library.
Hardware Overview
J1: used to connect Arduino IIC Interface as Grove - I2C ADC output interface.
J2: used to connect analog sensor as Grove - I2C ADC input interface.
U1: ADC121C021 IC,12-Bit Analog-to-Digital Converter
The black line area is used to set the IIC address. ADDR0 and ADDR1 are
shipped connected to L. You can change them to “H” or floating by a little
modification on the board(floating is neither connec ting “H” nor connect ing
“L”). Find details in the Reference.
Getting Started
With Arduino
Grove - I2C ADC has two interfaces: input socket(J2) and output socket(J1). Connect
an analog sensor to its input socket and connect the I2C ADC to Arduino/Seeeduino
also via Grove cables.
Take Grove - Gas Sensor as an example, and now we learn how to read sensor data
using Grove - I2C ADC. The hardware installation should be like this:
Now you can read the gas sensor value using the code below.
#include <Wire.h>
#define ADDR_ADC121 0x55
#define V_REF 3.00
#define REG_ADDR_RESULT 0x00
#define REG_ADDR_ALERT 0x01
#define REG_ADDR_CONFIG 0x02
#define REG_ADDR_LIMITL 0x03
#define REG_ADDR_LIMITH 0x04
#define REG_ADDR_HYST 0x05
#define REG_ADDR_CONVL 0x06
#define REG_ADDR_CONVH 0x07
unsigned int getData;
float analogVal=0; // convert
void init_adc()
{
Wire.beginTransmission(ADDR_ADC121); // transmit to device
Wire.write(REG_ADDR_CONFIG); // Configuration Register
Wire.write(0x20);
Wire.endTransmission();
}
void read_adc() //unsigned int *data
{
Wire.beginTransmission(ADDR_ADC121); // transmit to device
Wire.write(REG_ADDR_RESULT); // get result
Wire.endTransmission();
Wire.requestFrom(ADDR_ADC121, 2); // request 2byte from device
delay(1);
if(Wire.available()<=2)
{
getData = (Wire.read()&0x0f)<<8;
getData |= Wire.read();
}
Serial.print("getData:");
Serial.println(getData);
delay(5);
Serial.print("The analog value is:");
Serial.print(getData*V_REF*2/4096);
Serial.println("V");
}
void setup()
{
Serial.begin(9600);
Wire.begin();
init_adc();
}
void loop()
{ read_adc();//adcRead);
delay(50);
}
In the code above, we defined the Vref as 3.0V which is decided by the I2C ADC
module. This reference voltage is more accurate than one generated by
microcontroller. And you can make that more accurate by measuring the voltage
between VA and GND and use that value to replace 3.00 in the code above.
Now you can upload the code.
Afterwards, open the serial monitor and read the values:
Note
The address of Grove - I2C ADC is changeable which means you can redefine its address.
That requires some hardware modification on the board. If you are thinking about using more
than one I2C ADCs at the same time, follow the instructions in the Reference part below to
do so. The maximum number of I2C ADCs that can be used simultaneously is 9, but there
are only 4 I2C sockets on Grove - Base Shiel d V1 .2, so if you want to use more than 4 I2C
ADC, take a Grove - I2C Hub to create more I2C sockets.
With Beaglebone Green
To begin editing programs that live on BBG, you can use the Cloud9 IDE. As a
simple exercise to become familiar with Cloud9 IDE, creating a simple application to
blink one of the 4 user programmable LEDs on the BeagleBone is a good start.
If this is your first time to use Cloud9 IDE, please follow this link.
Step1: Set the Grove - UART socket as a Grove - GPIO Socket, just follow this link.
Step2: Click the “+” in the top-right to create a new file.
Step3: Copy and paste the following code into the new tab
from Adafruit_I2C import Adafruit_I2C
import time
ADDR_ADC121 = 0x50
REG_ADDR_RESULT = 0x00
REG_ADDR_ALERT = 0x01
REG_ADDR_CONFIG = 0x02
REG_ADDR_LIMITL = 0x03
REG_ADDR_LIMITH = 0x04
REG_ADDR_HYST = 0x05
REG_ADDR_CONVL = 0x06
REG_ADDR_CONVH = 0x07
i2c = Adafruit_I2C(ADDR_ADC121)
class I2cAdc:
def __init__(self):
i2c.write8(REG_ADDR_CONFIG, 0x20)
def read_adc(self):
"Read ADC data 0-4095."
data_list = i2c.readList(REG_ADDR_RESULT, 2)
#print 'data list', data_list
data = ((data_list[0] & 0x0f) << 8 | data_list[1]) & 0xfff
return data
if __name__ == '__main__':
# Connect the Grove - I2C ADC to I2C Grove port of Beaglebone Green.
adc = I2cAdc()
while True:
print 'sensor value ', adc.read_adc()
time.sleep(.2)
Step4: Save the file by clicking the disk icon and giving the file a name with the .py
extension.
Step5: Connect Grove I2C ADC to Grove I2C socket on BBG.
Step6: Run the code. You’ll find that the terminal outputs AD value every 2 seconds.
Reference
I2C Addr es s Setting
The ADC I2C has a seven-bit hardware address which is decided by ADR0 and
ADR1. ADR0 and ADR1 are connected to L inside the board as default. But you can
change it. For example, use a knife to cut off the connection between L and ADR0(as
the picture shown below), then you make the state of ADR0 into Floating(connected
to nothing). And if you solder up ADR0 and H this time, then you make the value of
ADR0 H.
ADR0 and ADR1
inputs state
ADR1
ADR0
1010000(0x50)
Floating
Floating
1010001(0x51)
Floating
L
1010010(0x52)
Floating
H
1010100(0x54)
L
Floating
1010101(default 0x55)
L
L
1010110(0x56)
L H 1011000(0x58)
H
Floating
1011001(0x59)
H
L
1011010(0x5A)
H
H
You can find the relationship of hardware I2C address and the values of ADR0 and
ADR1 in the following table.
Slave Address[A6 -
A0]
How much does the I2C A D C increase the acc ur acy ?
Here is an experiment we make to give you a sense about how much the I2C ADC
increase the accuracy of an analog sensor. First, let’s check the values collected
directly through analog port on Arduino/Seeeduino from an Grove - Gas
Sensor(MQ5)
We upload the code below to get the data.
/*
* Grove - Gas Sensor(MQ5)
*
* The Gas Sensor detect the related Gas density,
* Arduino get the result by analogread. the gas Density is
* 0~1, larger the output is, the denser the gas.
* Connect the Sensor to A0 in this demo;
*
* By: http://www.seeedstudio.com
*/
#define Vref 4.95
void setup() {
Serial.begin(9600);
}
void loop() {
float vol;
int sensorValue = analogRead(A0);
vol=(float)sensorValue/1023*Vref;
Serial.print("The sensorValue is ");
Serial.println(sensorValue);
Serial.print("The analog value is ");
Serial.print(vol);
Serial.println("V");
delay(100);
}
The result is:
As default, Vref is generated by Arduino which is theoretically 5V. But actually that is
a value afloat which results the deviation of the final data. This kind of inaccuracy is
avoided when using Grove - I2C ADC, because it provides a strict 3.0V as Vref. To
contrast, in the same condition, sensor values collected by the circuit with Grove I2C ADC in the scope is shown below:
In order to find out which result is more close to the actual condition, here we use a
multimeter to measure the voltage between the pin SIG and pin GND of the sensor.
Loading...