AVR-Microcontroller
in the Ham-Shack

back

next

The APRS Telemetry Interface

The Digital Channels

The Interface has two groups of digital inputs.

1st Group

The first group has 8 digital inputs, TTL-level, connected to P19, Digital/Counters. You can choose digital input or frequency counter input by reading the right channel.

You can check the digital inputs via the serial port. Type the command "RD 1" (Read Digital 1) and the interface will send the actual values of the input lines as eight bits, "0"/"1" every second. This testmode does not influence the connection between the interface and DIGI_NED. Type "q" to stop the testmode.

As default setting the digital channels are connected to DIGI_NED-address 7. You are free to change this setting by the channel matrix.

2nd Group

The second group has 6 input bits. Each of these input lines has a second special function.

• 4 TTL-level inputs. They are conncted to P16, I2C/Dig. You find the values of the inputs on Bits 1,2,3 and 4 of the second digital channel.
  Special Functions:  
  • Voltage comparator:
    The inputs PB2 and PB3 of the controller are connected to a voltage comparator inside the controller. If the voltage at PB3 is lower than the voltage at PB2, the output of the comparator is set to "1" else it is set to "0". This result can be read as bit 6 of the second group. Voltage range at both inputs is 0 to 5V.
  • I2C-Bus:
    You can connect I2C-bus devices to inputs PB2 and PB3 of the controller. The comparator is not usable in this case.
  • Event Counter, Low Frequency Counter:
    Input PB0 is connected to the Event Counter 1 and the Low Frequency Counter 1.
    Input PB1 is connected to the Event Counter 2 and the Low Frequency Counter 2.
• WD-In is the fifth input. It has a special input cirquit to get higher voltage levels than 5V-TTL. The voltage may be even negative. Negative voltages and positve voltages below 1V are read as "1" higher positive voltages are read as "0". Maximum is 20V. You find this value on bit 5 of the second digital channel.
  Special Functions:
  • This input is used by the PC-/ TX-Watchdog.
  • It is connected to the Event Counter 3 and the Low Frequency Counter 3.

You can check the digital inputs via the serial port. Type the command "RD 2" (Read Digital 2) and the interface will send the actual values of the five input lines and the result of the comparator as six bits, "0"/"1" every second. This testmode does not influence the connection between the interface and DIGI_NED. Type "q" to stop the testmode.

If you want to read the second group of digital channels by DIGI_NED, you have to connect this channel to a DIGI_NED channel by an "MM"-command first. Bits 7 and 8 are unused and they allways read "0" in DIGI_NED.

Configuration in DIGI_NED

Entry in "digi_ned.ini":

telemetry: 30 1 off,off,off,off,off,lpt1_8/7 DIGI_DEST

This means: Send the telemetry data every 30 minutes via port 1. The analog channels are switched off in the example. The last entry defines the DIGI_NED-address 7 for the digital channels on LPT1 in 8 bit mode.

Query to the digipeater

Send a message "tlm b" to the digipeater.
It will answer (if you have the pattern 10101010 at the inputs):

B1-B8 value 10101010

If you send the message "tlm b1" to the digipeater, you will get the value of digital input 1.
The digipeater will answer:

B1 is hi

The exact format of the output is defined in the file "digi_tlm.ini".

back

next

Home

Top

Burkhard John

5.7.2006