EXPERIMENT
#10 PRELAB
By now you should have an idea about which philosophy
you want to use to navigate the track, stop on a white
piece of paper, and navigate the split. It is best to
design these functions seperately and combine them together
with a block of decision-making logic.
Depending on the signals split detect, and
stop detect the decision-making circuitry sends
the appropriate L and R signals to the motors. Lets design
a simple decision-making ciruit.
Track navigating circuitry: any one of the
designs that we have tried or any of your own design. By
default, the vehicle will follow these signals unless
special signals are seen. We will be overriding this
circuit with the color/split detect circuit and the
stopping circuit.
Color detecting and split navigating
circuit: this circuit generates two control
signals, i) a signal that goes high when the presence of
colored tape has been detected (C) and ii) a signal that
goes high when a split in the path has been detected (S).
The control signal that is used to override the track
navigating will be the signal S, the signal C is used to
determine how to turn, that is how to generate the signals
R and L properly but is not used as a control signal.
Subsequent references to S will refer to this split
detecting signal.
Stop detecting circuitry: this circuit
determines the proper condition for stopping and generates
an signal that is high when the stop condition is met (A).
Some notes on the stopping circuitry - some of the designs
like the tape avoiding designs stop automatically when on a
white piece of paper. Some people design seperate sensors
to look for a white piece of paper. CAUTION: depending on
the outputs from sensors located along a single sensor bar
is risky because it is an easy combination to duplicate
when running the track. Whatever your circuitry for
stopping lets say that it generates its own condition
signal A. When A=0, ignore the stop signal, when A=1 stop.
Now lets combine the control signals S, and A (as defined
above - A for arrete) with the L and R signals from each
function to determine the final L and R signals sent to the
motor.
- If your circuitry detects the
presence of a split, and the stop condition is not
satisfied (remember you want to turn right on red) ->
S=1 A=0 What set of L/R signals should the L and R output
to the motors follow?
- If your
circuitry detects no split, but a stop condition ->
S=0 A=1 What signals set of L/R signals should the L and
R that are output to the motors follow?
- When S=0 A=0
what should happen?
-
Translate the
above conditions on to the table below to summarize
them. Some of the entries are filled in.
This decision-making circuit can be implemented with the following circuitry - but there is a much simpler way of doing this, lets see what it is.
- Hum....this behaves a lot like a
module that you have studied in class. Remember the
multiplexer? Suppose we have the 74LS153 available to us,
replace the above circuit with one using this dual 4:1
multiplexer. Below is a picture of the logic symbol for
the device. The signals So and Sa
are the signals that are used to select which of the
inputs to connect to the outputs. For example, if
So=0 and Sa=0 then I0a
shows up on Za and Ibo shows up on
Zb. Always set the enable pins low -
Ea and Eb. Implement your table
that you filled in for the previous part using two
multiplexers - one for the left signal L and one for the
right signal R.
During the lab you will be asked to make a preliminary
choice for your circuit design - be prepared. The remainder
of the labs need to be used to hone your design. USE YOUR
TIME WISELY. Look at how the points will be awarded for
different parts of the track. If you are having trouble
getting your circuit to work on certain portions of the
track, concentrate on other parts. Consider these points in
developing a strategy for using your time. You must
complete the gentle turns and zip-zags before attempting
the right-angle turns. You have 5 tries - use them wisely -
read the rules on the home page carefully. You can do each
split in the path seperately, but they are connected to the
rest of the path so if you are successful at navigating the
right-hand turns, for instance, your vehicle encounters one
of the splits so you do not have to take an extra try.
EXPERIMENT #10
a)
adding the decision making
circuitry -
- implement the circuit that was
discussed in the prelab that integrates track following,
the split detection, and stopping circuits. Test it on
the track. Does it behave correctly? Note, your design
may integrate the stopping function with your track
navigation automatically, then you only need a 2:1
multiplexer.
b) testing different designs -
This is the end of your formal labs. You will be using the next weeks to hone a design that will run during the final week of the lab class. As the final part of this lab pick a strategy that you think that you might use in your final design - tape-following/tape-avoiding or some combination, will you use speed control, perhaps the CAB module. Take the circuit that you have chosen and experiment with parameters like sensor placement and combinations, speed, sensor height, etc...
- Document with figures, tables,
and design philosphy describing your basic idea for track
navigation, split navigating, and stopping. Then
experiment with three different modifications to this
basic design in your lab notebook. Modifications can
include trying different sensor placements, trying to
integrate the PWM or CAB module into your design. The
speed control of the PWM buys you alot and backing up
when you lose the tape (CAB) can also be a very simple
but powerful design element. But what every your choices
- during this lab period document in your lab notebooks
three different modifications to your basic design. Your
design may change before the end - that is fine. You will
not be held to these designs. This is simply to encourage
you to try different configurations.