1        Introduction

The IRLP IO Interface has the DTMF decoder installed on the board along with some other circuits that support the COS and PTT logic levels along with AUX outputs.

The DTMF decoder has a LED connected to the DTMF valid line via an open collector driver. When the DTMF is valid, the led is turned on. This is of great use to see if the node hardwae is receiving the DTMF signals from the radio. The only problem is, you need to have the cover off the PC to see if the LED lights up or not.

The AREG designed MOD to the IRLP IO Interface allows the active low signal to be connected to the 10pin IDC pin header and thus to the AREG IRLP Audio Interface where some additonal led drivers can provide a drive signal to an LED mounted on the outside of the computer case.

This modification should not be attempted by anyone that is not accredited to IPC rework and repair, or a suitable equilivant skill level. Also your warranity on the IRLP IO Interface will be void, so ensure it works correctly before trying the mod.

For a pdf copy please refer to, IRLP_IO_Interface_Version_3_DTMF_wire_modification_Rev_3.pdf

IRLP IO Interface Version 3.0 DTMF Led Modification

When using the AREG Audio Interface with the IRLP IO Interface Version 3.0 a modification is required before the DTMF Led will work on the AREG Audio Interface.

The purpose of the DTMF Led and front panel connector J5 on the AREG interface are only to provide an additional LED that can be mounted on the outside of the computer case. This may be useful if you need to fault find the system.
The DTMF led and the associated circuits on the AREG Audio interface do not affect the operation of the IRLP node in any way. If you elect not to modify the IRLP IO Interface version 3.0 by adding an additional wire, the only thing that will not work is the LED on the AREG board.

The critical part is; if DTMF is being received by the radio, the led on the IRLP IO Interface lights up. The lighting up indicates that valid DTMF has been decoded.

Modification Details
An additional wire needs to be installed between the DTMF LED on the IRLP IO Interface PCB and the 10 Pin header connector on the IRLP IO Interface PCB. Install a small 30 AWG wire between the points shown in the following photos of the PCB. Ensure all solder dags are removed and not small bits of wire are left as they may cause the IRLP IO Interface to stop working.

WARRANING
Persons qualified to conduct circuit board repair and surface mount soldering should only attempt this modification.
Modification of the IRLP IO Interface Version 3.0 is done so at your own risk, and the author of this document implies or accepts no warranty for the information provided.

Connecting the IRLP IO Interface to AREG Audio Interface

The problem with the IRLP IO Interface is the 10 Pin header connector does not follow standard IDC pin outs, and only the standard cable that comes with the board or a cable that has been wired correctly will work between the IRLP IO Interface and the AREG Audio Interface (AAI)

Standard IDC Connector Layout
An IDC connector with ribbon cable terminated on it, has a small arrow denoting pin 1. The first conductor of the ribbon cable is usually denoted by a red strip, and the subsequent conductors are grey in colour, for multicoloured ribbon cable the wire on the out side nearest the arrow denoting pin one.

As an example in a 10 pin IDC connector that has two rows of 5 pins. The second conductor in the ribbon cable, that is the wire next to first conductor has a corresponding pin directly across from pin one.

IRLP IO Interface Header Connector
The IRLP IO Interface Header Connector has been designed differently, and if you consult the documentation that comes with the board, the pin layout is very different.

 

Version 1.1 of AREG Audio Interface has been designed, a straigh through IDC cable will be required. The following table shows the pins as layout on the IRLP IO Interface and how they correspond to a standard IDC connector and the connextor X4 on the AREG IRLP Audio Interface version 1.1.

IRLP IO InterfaceJ5 – 10 Pin Header	Standard IDC Connector	AREG Audio Interface X4- 10 Pin IDC Header
1 (Not Used)	1 (Not Connected)	1 (Not Connected)
2 (PTT Output)	3	3 (PTT Input)
3 (AUX 1 Output)	5	5 (AUX 1 Input)
4 (AUX 2 Output)	7	7 (AUX 2 Input)
5 (AUX 3 Output)	9	9 (AUX 3 Input)
6 (GND)	2	2 (GND)
7 (COS Input)	4	4 (COS Output)
8 (DTMF Audio Input)	6	6 (DTMF Audio Output)
9 (DTMF Valid – Active Low Signal, only after mod has been completed)	8	8 (DTMF Valid Input)
10 (Not Used)	10 (Not Used)	10 (Not Connected)

NOTE !

AREG IRLP Audio interface has been updated to version 1.1, the cable shown below is only for reference and use with version 0.4 boards only.

Cable - IRLP IO Interface Version 3.0 to AREG Audio Interface Version 0.4

Until the next version of the AREG Audio Interface has been designed, a special cable will be required. The following table shows the pins as layout on the IRLP IO Interface and how they correspond to a standard IDC connector and finally to the 9 Pin connector used on the AREG Audio Interface.

IRLP IO InterfaceJ5 – 10 Pin Header	Standard IDC Connector	AREG Audio InterfaceJ4 - 9 Pin D Connector
1 (Not Used)	1 (Not Connected)
2 (PTT Output)	3	2 (PTT Input)
3 (AUX 1 Output)	5	3 (AUX 1 Input)
4 (AUX 2 Output)	7	4 (AUX 2 Input)
5 (AUX 3 Output)	9	5 (AUX 3 Input)
6 (GND)	2	6 (GND)
7 (COS Input)	4	7 (COS Output)
8 (DTMF Audio Input)	6	8 (DTMF Audio Output)
9 (DTMF Valid – Active Low Signal, only after mod has been completed)	8	9 (DTMF Valid Input)
10 (Not Used)	10 (Not Used)	10 (Not Connected)

AREG Audio Interface (AAI)

The 9 Pin D Type connector required on the cable is a male type, and the pin numbers are usually printed on the connector.

Testing the operation of the MOD

The modification can be easily tested by using a pull up resistor (1K ohm ¼ Watt) and LED with the one end of the resistor connected to +5 Volts using a spare hard disk power connector. The other end of the resistor connected to the Anode of a LED and the Kathode of the LED connected to pin 9 of the IRLP IO Interface 10 pin header, see previous image for pin configurations. An audio signal will need to be feed into pin 3 at a suitable level so the DTMF decoder on the IRLP IO Interface detects valid DTMF and thus turns the led on the PCB.

This testing can also be conducted using the radio connected to the AREG Audio Interface, and an other transmitter, generate a RF signal with DTMF tone on it. The LED should turn on once enough audio level is being received by the DTMF decoder IC.

IRLP I/O Interface PCB documentation please refer to the IRLP Web site for the latest copy, or downloade copy on 26/4/2009 for detail. IRLP_IO_Interface_Ver3_Wiring.pdf

Happy playing with IRLP.