ADC Interface with Ultrasonic Proximity Sensor - Revision history

Preet at 17:09, 6 November 2013

2013-11-06T17:09:06Z

Preet: /* Sample Code */

2012-11-15T19:50:01Z

‎Sample Code

Charley: Created page with " == Overview == The LV-MaxSonar-EZ0 ultrasonic sensor interfaces with your microcontroller using an ADC interface. The microcontroller on your development board is equipped w..."

2012-11-15T18:54:25Z

Created page with " == Overview == The LV-MaxSonar-EZ0 ultrasonic sensor interfaces with your microcontroller using an ADC interface. The microcontroller on your development board is equipped w..."

New page

== Overview ==

The LV-MaxSonar-EZ0 ultrasonic sensor interfaces with your microcontroller using an ADC
interface. The microcontroller on your development board is equipped with an analog-to-digital
converter. This converts an analog signal (continuous voltage that varies over time) into
corresponding digital values (discrete integers that approximate the input voltage). For example,
let’s say that a 12-bit ADC operates on 3.3V, which is the case for your SJSU One development
board. This means that a voltage range between 0V and 3.3V can be divided into 212
or 4096 discrete steps. If the ADC is returning an integer value of 2048, you can calculate that a sensor
connected to the ADC is outputting a voltage of 1.65 volts.

== Pin Connections ==

The ultrasonic sensor has 7 pins. We will connect 3 of them to your board:
# Use a red wire to connect Pin “+5” on the sensor to Pin “3.3V” on your board.
# Use a black wire to connect Pin “GND” on the sensor to Pin “Gnd” on your board.
# Use another color wire to connect Pin “AN” on the sensor to Pin “A0-4” on your board.

== Source Code Description ==

Add <code>#include “adc0.h”</code> to the top of your main.c. This gives you access to the ADC
functions.

Your microcontroller has 80 pins but many more features. Therefore, one pin can do many
different things. We will need to tell it to internally connect pin P1.30 to the ADC
hardware as opposed to some other hardware. To do this we will need to write the
appropriate value to a Pin Select Register:

<code>LPC_PINCON->PINSEL3 |= (3 << 28);</code>

A function has been written to initialize ADC functionality. This function can be called
by:

<code>adc0_initialize();</code>

Now, you can read values from the ADC with a call to:

<code>adc0_getReading(4);</code>

The “4” represents that we are reading values from ADC channel 4. Your board has multiple
ADC channels. For example, the light sensor is connected to channel 2, so we can’t use
that one.

== Sample Code ==

<syntaxhighlight lang = "c">
#include “adc0.h”

int main(void)
{
int reading;

LPC_PINCON->PINSEL3 |= (3 << 28); // ADC-4 is on P1.30, select this as ADC0.4
adc0_initialize(); // Initialize ADC
reading = adc0_getReading(4); // Read current value of ADC-4
printf("\nADC Reading: %d", reading);

return 0;
}
</syntaxhighlight>


== Remaining Work ==

Your job is to turn the integer values you receive from ADC into numbers that are more
useful. Do this by converting the ADC value into a voltage value. Next, convert the
voltage value into a distance measurement value. The conversion rate needed to convert
voltage to inches/centimeters is in the sensor data sheet, which I will leave for you to
find.

== Adding a second ADC type sensor ==

It is possible to connect a second sensor that uses ADC to your board using ADC Channel
5. This will require a different pin select code so ask a TA for assistance.

@@ Line 1: / Line 1: @@
 == Overview ==
@@ Line 29: / Line 28: @@
 <font size = 3><code>LPC_PINCON->PINSEL3 |= (3 << 28);</code></font>
 Now, you can read values from the ADC with a call to:
-<font size = 3><code>adc0_getReading(4);</code></font>
+<font size = 3><code>adc0_get_reading(4);</code></font>
 The “4” represents that we are reading values from ADC channel 4. Your board has multiple
@@ Line 54: / Line 48: @@
      // Initialization :
      LPC_PINCON->PINSEL3 |=  (3 << 28); // ADC-4 is on P1.30, select this as ADC0.4
      while(1) {
-         reading = adc0_getReading(4); // Read current value of ADC-4
+         reading = adc0_get_reading(4); // Read current value of ADC-4
          printf("\nADC Reading: %d", reading);
          delay_ms(1000);
+     }

@@ Line 50: / Line 50: @@
 int main(void)
+{
-     int reading;
+     int reading = 0;
      LPC_PINCON->PINSEL3 |=  (3 << 28); // ADC-4 is on P1.30, select this as ADC0.4
      adc0_initialize(); // Initialize ADC
      reading = adc0_getReading(4); // Read current value of ADC-4
-    printf("\nADC Reading: %d", reading);
+     while(1) {
      return 0;