CSCE 236 Embedded Systems, Spring 2012
In Class: Thursday, February 23, 2012
Names of Group Members:
This is a group assignment to work on during class. You only
need to hand in one copy of this, but make sure that the names of all
of your group members are on this sheet to receive credit. Complete
all of the sections below and make sure to get the
instructor or TA to sign off where required.
2 Manual Analog to Digital Converter
In this section of the lab, you will manually configure the analog to
digital converter (also know as ADC or A2D). You will then test it by
creating a voltage divider and reading the values at different points
on the voltage divider.
Refer to the datasheet and configure the ADC in the setup function by:
Now create a voltage divider on your bread board using 3 different
resistors (of your choosing, whatever you have available). Connect 1
end of the divider to ground and the other to the 5V power rail. Now
connect an ADC port to each of the 4 different voltage levels created
by the voltage divider (GND, between R1 and R2, between R2 and R3, and
In your loop function, write code to read each of the 4 ADC values and
output the four values over the serial port. To read the ADC, you must:
- Setting the ADC voltage reference to AVcc. This connects the
voltage reference to the external voltage supply, which on the
Arduino is 5V.
- Enabling the ADC by setting the appropriate bit in the
- Setting the ADC clock prescaler to an appropriate value for the
Arduino. Refer to table 24-5 in the datasheet. As noted, in
section 24.4, the successive approximation circuitry in the ADC
requires an input clock frequency between 50kHz and 200kHz.
Checkoff: What clock divider did you end up using and what is
the final ADC clock value?
- Set the ADCMUX register appropriately (do not overwrite
the voltage source bits).
- Start the conversion (look for ADCS bit).
- Wait for the conversion to complete (by monitoring the ADCS bit).
- Read the value out of the ADC register.
Checkoff: How do you convert from the ADC value to the actual voltage
on the pin? Do the voltages you read on your voltage divider match
the theoretical values given the resistor values you have?
3 Reflectance Sensor
In this section of the lab, you will hook up infrared (IR) reflectance
sensors to your robot. These sensors emit an IR light and then
measure how much is reflected back. If the IR sensor is over a white
surface a lot of IR will be measured, while if it is over a black
surface little will be seen. The distance to the surface also makes a
For this part of the lab, you can either read the ADC manually as
you configured it above, or use the Arduino analogRead(...)
command. I would recommend using the analogRead(...)
command or creating functions that encapsulate the ADC reading code
above. Regardless, you are expected to know how both work.
The reflectance sensors have three wires. Black should be connected
to ground, red to 5V, and the green wire to one of your ADC ports.
Perform basic experiments to characterize the performance of the
sensors. You can use the black line on the following page as a
Checkoff: As you move the sensor closer to a surface, does the ADC
value increase or decrease?
Checkoff: How close do you have to be to an object to have a
difference of more than 100 ADC values between a black and white
4 Project 1 Competition Overview
The first project competition will be held Tuesday, March 6, 2012. A
written report will be due Thursday, March 8, 2012. Additional
details on this competition and the report will be forthcoming.
As an overview, this competition will involve having your robot follow
a line as quickly as possible using the IR sensors. In addition to
speed, your robot will be judged on the smoothness of operation. Your
robots will compete against each other on a variety of courses
containing different types of curves and turns.
Start by mounting the IR sensors on your robot as demonstrated in
class. Then write code that will turn your robot towards a line if
one sensor sees the line and the other does not or to drive straight
if both sensors see the line. Start by using slow forward and turning
speeds, then try increasing the speeds so you can operate faster.
Initially you should transition between three different driving
states: straight, left turn, and right turn. Once you have this
working, you can try to create smoother turns by doing a more gradual
transition between these states or based on the values of the sensors.
You should also consider what action to take if your robot completely
looses sight of the line. You can use the line on the following page
as a reference.
Additional details on this competition, including questions you should
answer will be given next week. Note that this is an individual
assignment, but you can use time in lab to get started.
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On 26 Feb 2012, 12:40.