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.. _2.1.7_py:
2.1.7 Potentiometer
===================
Introduction
------------
The ADC function can be used to convert analog signals to digital
signals, and in this experiment, ADC0834 is used to get the function
involving ADC. Here, we implement this process by using potentiometer.
Potentiometer changes the physical quantity -- voltage, which is
converted by the ADC function.
Required Components
------------------------------
In this project, we need the following components.
.. image:: ../img/list_2.1.4_potentiometer.png
It's definitely convenient to buy a whole kit, here's the link:
.. list-table::
:widths: 20 20 20
:header-rows: 1
* - Name
- ITEMS IN THIS KIT
- LINK
* - Raphael Kit
- 337
- |link_Raphael_kit|
You can also buy them separately from the links below.
.. list-table::
:widths: 30 20
:header-rows: 1
* - COMPONENT INTRODUCTION
- PURCHASE LINK
* - :ref:`cpn_gpio_extension_board`
- |link_gpio_board_buy|
* - :ref:`cpn_breadboard`
- |link_breadboard_buy|
* - :ref:`cpn_wires`
- |link_wires_buy|
* - :ref:`cpn_resistor`
- |link_resistor_buy|
* - :ref:`cpn_led`
- |link_led_buy|
* - :ref:`cpn_potentiometer`
- |link_potentiometer_buy|
* - :ref:`cpn_adc0834`
- \-
Schematic Diagram
-----------------
.. image:: ../img/image311.png
.. image:: ../img/image312.png
Experimental Procedures
-----------------------
**Step 1:** Build the circuit.
.. image:: ../img/image180.png
.. note::
Please place the chip by referring to the corresponding position
depicted in the picture. Note that the grooves on the chip should be on
the left when it is placed.
**Step 2:** Open the code file
.. raw:: html
.. code-block::
cd ~/raphael-kit/python/
**Step 3:** Run.
.. raw:: html
.. code-block::
sudo python3 2.1.7_Potentiometer.py
After the code runs, rotate the knob on the potentiometer, the intensity
of LED will change accordingly.
**Code**
.. note::
You can **Modify/Reset/Copy/Run/Stop** the code below. But before that, you need to go to source code path like ``raphael-kit/python``. After modifying the code, you can run it directly to see the effect.
.. raw:: html
.. code-block:: python
#!/usr/bin/env python3
import RPi.GPIO as GPIO
import ADC0834
import time
LedPin = 22
def setup():
global led_val
# Set the GPIO modes to BCM Numbering
GPIO.setmode(GPIO.BCM)
# Set all LedPin's mode to output and initial level to High(3.3v)
GPIO.setup(LedPin, GPIO.OUT, initial=GPIO.HIGH)
ADC0834.setup()
# Set led as pwm channel and frequece to 2KHz
led_val = GPIO.PWM(LedPin, 2000)
# Set all begin with value 0
led_val.start(0)
# Define a MAP function for mapping values. Like from 0~255 to 0~100
def MAP(x, in_min, in_max, out_min, out_max):
return (x - in_min) * (out_max - out_min) / (in_max - in_min) + out_min
def destroy():
# Stop all pwm channel
led_val.stop()
# Release resource
GPIO.cleanup()
def loop():
while True:
res = ADC0834.getResult()
print ('res = %d' % res)
R_val = MAP(res, 0, 255, 0, 100)
led_val.ChangeDutyCycle(R_val)
time.sleep(0.2)
if __name__ == '__main__':
setup()
try:
loop()
except KeyboardInterrupt: # When 'Ctrl+C' is pressed, the program destroy() will be executed.
destroy()
**Code Explanation**
.. code-block:: python
import ADC0834
import ADC0834 library. You can check the content of the library by
calling the command nano ADC0834.py.
.. code-block:: python
def setup():
global led_val
# Set the GPIO modes to BCM Numbering
GPIO.setmode(GPIO.BCM)
# Set all LedPin's mode to output and initial level to High(3.3v)
GPIO.setup(LedPin, GPIO.OUT, initial=GPIO.HIGH)
ADC0834.setup()
# Set led as pwm channel and frequece to 2KHz
led_val = GPIO.PWM(LedPin, 2000)
# Set all begin with value 0
led_val.start(0)
In setup(), define the naming method as BCM, set LedPin as PWM channel
and render it a frequency of 2Khz.
**ADC0834.setup():** Initialize ADC0834, and connect the defined CS,
CLK, DIO of ADC0834 to GPIO17, GPIO18 and GPIO27 respectively.
.. code-block:: python
def loop():
while True:
res = ADC0834.getResult()
print ('res = %d' % res)
R_val = MAP(res, 0, 255, 0, 100)
led_val.ChangeDutyCycle(R_val)
time.sleep(0.2)
The function getResult() is used to read the analog values of the four
channels of ADC0834. By default, the function reads the value of CH0,
and if you want to read other channels, please input the channel number
in **( )**, ex. getResult(1).
The function loop() first reads the value of CH0, then assign the value
to the variable res. After that, call the function MAP to map the read
value of potentiometer to 0~100. This step is used to control the duty
cycle of LedPin. Now, you may see that the brightness of LED is changing
with the value of potentiometer.
Phenomenon Picture
------------------
.. image:: ../img/image181.jpeg