Reading the Games Port AtoD Lines in MSW Logo 6.4

Reading the Games Port AtoD Lines in MSW Logo 6.4
(NOTE: This feature is only available in Version 6.4 and above.)

(A standard Joystick has variable resistors on Line1 and Line2)

The <InGamePort MASK> function carries out an Analogue to Digital (AtoD) conversion based on the value of a resistance connected across a line at the Games Port. The function uses a counting 'loop' to carry out the conversion process. The value returned is proportional to the resistance. (ie a high resistance returns a high value - in general, the average resistance value should be in the order of 0 to100k ohms)

Make sure you have a resistance across each line being read or the counting loop will take quite a while to complete. If your system appears to 'hang' for a while it would indicate that one, or all of the lines you are reading does not have a resistance across it.

If you are sure you have resistances connected and it still 'hangs':
1. The Games port may not be installed properly, or it may be 'disabled'.
2. The cable socket may not be fully plugged in.

(NOTE: Either way, don't panic. The counting loop WILL end. It may take a little while. The actual time depends on how fast your system is. It could be a few seconds, or even several minutes. Don't be tempted reset the computer.)

For further information on the Games Port see:
http://www.southwest.com.au/~jfuller/logotut/games.htm

Displaying the Values of Each Line

to games1
; The general form is:
; make "InValue InGamePort X
; (Where "X" can be 1, 2, 4, or 8)
; SetXY is used to position the values
; across the screen
home
CS
Make "InValue1 InGamePort 1
SetXY -200 0
label :InValue1
Make "InValue2 InGamePort 2
SetXY -100 0
label :InValue2
Make "InValue4 InGamePort 4
SetXY 0 0
label :InValue4
Make "InValue8 ingameport 8
SetXY 100 0
label :InValue8
end

The interface used in these examples has three fixed resistances
and one variable resistor. The output from the procedure appears as:

gameport1a.gif (594 bytes)

If your system appears to 'hang' and the readings come up as "-1"
it means that the line reporting a "-1" has no resistance across it.
Either eliminate that line from the procedure, or add a resistor.

NOTE: On a standard joystick only lines 1 and 2 should be read.
The others are unlikely to have resistors attached.

Presenting the Values Read as a Graph

to games2
; In this procedure the value read on 'line1' is displayed
; graphically by using it as the 'vertical' value in SetXY.
; The state of the Games port is read in a loop controlled by the
; value of the variable "count1". The loop ends when count1
; reaches 400. Count1 is used as the Horizontal value in SetXY.
; InValue8 is divided by 2 to restrict the height of the 'graph'.
cs
make "count1 0
PU
make "InValue1 ingameport 1
SetXY :count1 - 200 :InValue1/2
PD
; The four lines above move the cursor to the starting point of
; the graph.
do.until [make "count1 :count1 + 1 ReadGames] [:count1 = 400]
end

to ReadGames
Make "InValue1 ingameport 1
SetXY :count1 - 200 :InValue1/2
wait 10
end

NOTE: The names of the variables are of no importance. I have chosen to use "InValue" and "count1" out of past habit. ANY names could be used.

As the joystick is moved the
display produced by the
procedure appears as:

gameport1b.gif (2667 bytes)

So What??? How can I use it?

There are two basic approaches:

1. Incorporate Joystick control into your procedues.
2. Connect 'sensors' to the Games port to measure environmental variables such as Light and Heat.

The second "approach" listed above offers the most exciting possibilities. You could simply push the legs of a Thermistor (temperature dependent resistor) or a Light Dependent Resistor (LDR) into the Games Port socket at the back of the computer and read changes in light, or temperature directly. The photograph below shows a more elegant approach using an extension cable and an 'interface' with screw connectors to attach your 'sensors'. A "Joystick Extension Cable" plugs into the socket and connects to the Games Port at the rear of the computer.

games.jpg (6538 bytes)

Some of the things you can do ...

1. Record changes in light and temperature as a graph.
2. Save the data to disk to be imported into a spreadsheet for later charting and analysis.
3. Connect an output interface to control electric fans and motors based on Light, or Temperature readings.
4. Compare Light and Heat transmission through various materials.
5. Construct your own 'sensors' based on 100k ohm potentiometers.
6. Use MSW Logo in Science experiments.
7. Use a Joystick to control a remote-controlled vehicle.
8. Develop software for the disabled.
9. Make models of Industrial processes.
10. Measure changes in soil moisture content.
11. Measure changes in skin conductivity (A "Lie Detector"?)
12. ....etc, etc.

For further details about measuring Light and Heat see: http://www.southwest.com.au/~jfuller/logotut/logo22.htm
For information on capturing data to disk see: http://www.southwest.com.au/~jfuller/logotut/logo24.htm
For information on using the Games port in Science experiments download: http://www.southwest.com.au/~jfuller/scikit.zip

Displaying Input as a Graph ...

control4.jpg (49600 bytes)

MSW Logo Screen Shot

In the above screen-shot, buttons have been added for control and the oputput is displayed on a 'grid'. (I don't claim the code to be well written. If you decide to write more elegant procedures, please send me a copy.)
Download the MSW Logo file.

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