void setup() {
pinMode(5, OUTPUT); //A1
pinMode(6, OUTPUT); //A2
pinMode(7, OUTPUT); //A3
pinMode(8, OUTPUT); //B1
pinMode(9, OUTPUT); //B2
pinMode(10, OUTPUT); //B4
pinMode(11, OUTPUT); //C1
pinMode(12, OUTPUT); //C2
pinMode(13, OUTPUT); //C4

}

void loop() {
digitalWrite(5, HIGH);
digitalWrite(6, HIGH);
digitalWrite(7, HIGH);
digitalWrite(8, HIGH);
digitalWrite(9, HIGH);
digitalWrite(10, HIGH);
digitalWrite(11, HIGH);
digitalWrite(12, HIGH);
digitalWrite(13, HIGH);
digitalWrite(9, LOW);
digitalWrite(13, LOW); //700
delay(3000);
digitalWrite(8, LOW); //800
delay(3000);
digitalWrite(12, LOW); //900
delay(3000);
digitalWrite(13, HIGH); //1000
delay(3000);

}

I need to be able to simulate and encoder at home.  I am building one on my Duemilanove board.

The pinout is as follows

Enc Funct Arduino

1. N/C
2. A1     5
3. A2     6
4. A4     7
5. B1     8
6. N/C
7. N/C
8. N/C
9. B2     9
10. B4     10
11. C1     11
12. C4     13
13. C2     12

I figure I can find a sequence or set of decoded altitude numbers where I can have most pins remain the same, change one pin to jump to some other number, wait 3 seconds, change another pin, wait, change another.  I will use this sequence to make sure that my decoder is accurately decoding the change.

The digital pins operate at 5V. What will happen when they are connected to a 14v/28v encoder/ what is the pulled up value (voltage) of a pin on the encoder?

It looks like the transponder or other device is what pulls up the signal so I dug out this spec from the Trans-Cal SSD-120-30N manual

Driver Description: The parallel altitude data output is provided by the “uncommitted”
collectors of a transistor array and must be “pulled-up” through a resistive load by the
transponder.
Pull-Up Voltage: +3 to 40Vdc.
Maximum Sink Current: 50 mA.
Maximum Cable Length: 4000 ft. (1219 meters)
Input Signal Requirement: Pin 6 (strobe or signal common) must be either grounded or
connected to the transponder.

Digital pins do have a pull up resistor available.

The maximum DC current per I/O pin is 40mA.   I don’t want to burn up pins on my $50 mega board.  Do I have to do anything special so I don’t pull too much current when I pull the mega’s pins up to 5V?  I believe this is an internal function of the mega becuase it has internal pull up resistors that are selectable (I have to look this up) on each pin.

All ICAO altitude parallel outputs will be pulled low for a self test at power up, then assume the value for the present input pressure.