It has occurred to many that the board could be easily made for very little expense. However there is no official schematic for the interface board. Maybe you are interested in messing with a Linux based repeater controller. Or are I need of a spare IRLP board for interim node setups and testing.
Per the FAQ, they tell you that you cannot build your own board, this is only because nothing but problems and headaches have come to the mailing list so far from user-built boards. The mailing list is very busy with other trouble shooting issue and various questions. They just simply don't want to have to deal with user-built hardware issue. So if you know what you are doing, go right a head and build one, but please do not ask for help on the mailing list regarding it.
The male DB-25 on the IRLP board connects with a supplied short male to female DB-25 extension cable to the printers parallel printer port. The male DB-9 strap that connects to the main board has all the radio connections for interfacing to ones repeater / radio. The board is designed to mount into two spare PCI computer slots, as the Version 3 board has an on-board 4 conductor male molex connector for connection to the computer power supply. The 5 volt DC lines actually power the board. There is also PTT lockout jumper allows DTMF commands to be received when the transmitter is transmitting, for duplex environments (not the default position).
As seen here, Kyle, K0KN has
designed a schematic for people in these situations, to emulate the IRLP
board. Otherwise
you might find some people willing to part with theirs on the IRLP mailing list.
This schematic has nearly every feature and capability of the IRLP v3 board, that sells for $105, and can be constructed for about $25. An important financial consideration is that many manufacturers of personal computers and laptops consider parallel to be a legacy port and no longer include the parallel interface. (David Cameron, VE7LTD (IRLP System Designer) reported 12/06 & 11/07 that he is working on USB based solution, or a non parallel port IRLP interface card as these are being faded out in modern computers, even more so in embedded systems.)
Parts List:
| QTY | ICs | QTY | Resistors | QTY | Misc |
| 1 | HCF-4081 (Dual 4 Input And Gate) | 7 | 330 ohm | 1 | 1N914 Diode |
| 1 | MT8870 (Mitel CMOS Integrated DTMF Receiver) * | 1 | 820 ohm | 7 | LEDs |
| Capacitors | 5 | 1 k ohm | 1 | male DB-25 (right angle PCB mount) | |
| 1 | 0.1 uF | 4 | 2.2 k Ohm | 1 | male DB-9 (right angle PCB mount) |
| 1 | 0.01 uF | 6 | 3.3 k ohm | ||
| 1 | 10 k ohm variable | 1 | 3.579 MHz reference crystal | ||
| 1 | 100 k ohm | ||||
| 1 | 2.2 m ohm |
* (The MT8870 is becoming hard to find. In 2001, Mitel was split into two parts. The original company retained the semiconductor division. It was renamed Zarlink Semiconductor. It is unknown to me if the original MT8870 exists under a new part number, or if it just no longer being produced.)
More information on the IRLP board wiring, interfacing to your radio, audio wiring and other installation notes can be found here: http://www.irlp.net/new-install/
The IRLP board is a very simple circuit, the most difficult part being the on-board DTMF decoder. The DTMF decoder is comprised of a MT8870 (or similar) DTMF decoder IC and HCF4081 (or similar) and-gate IC. The MT8870 uses digital counting techniques to detect and decode all 16 DTMF tone-pairs into a 4-bit code Two chips are needed because the MT8870 has latched outputs, and the IRLP software looks for short pulses at the parallel port pins 10,12,13,15 in order to acknowledge a DTMF digit. MT8870 pin 15 provides a pulse when any valid DTMF digit is decoded, so this signal is used on one input of each gate on the HCF4081. The other gate input is from MT8870 pins 11,12,13,14. The output of the HCF4081 (pins 3,4,10,11) connect to the parallel port and provide the pulsed input that IRLP needs.
The external DTMF decoder helps to ensure you have dull duplex control at all times, no matter what the state of /dev/dsp.. The decoded digits hit the custom_decode file where you can script/define functions. It is well designed as the COR can be active high or active low. The COS jumper on the board switches between active high and active low. Also the voltage swing point of the COS can also be adjusted with the LGC SEL jumper. The COR must swing above and below 2.7 volts in one position and in the other, you can set that swing point to 1 volt.
IRLP uses the following parallel port pins:
3 PTT
4 Aux pin 1 (active high at parallel port)
5 Aux pin 2 (active high at parallel port)
6 Aux pin 3 (active high at parallel port)
10 DTMF 4
11 COS
12 DTMF 3
13 DTMF 2
15 DTMF 1
18-25 Ground
A few things to point out and clarify:
If you build your own you obviously don't get a an IRLP node number to coincide. This comes when you fill out an order form and payment. The IRLP board is $105. They also suggest a $40 donation. The IRLP software can be downloaded to save some cost. But if you wish, when you order the IRLP board you can get a pre-made ISO IRLP software disk that is provided by VE7LTD (David Cameron) for a cost of an extra $30.
http://tech.groups.yahoo.com/group/rtpDir/message/1266:
Date: Sat, 27 Dec 2008 17:55:47 -0800
To: rtpDir@yahoogroups.com
From: Stephen Rodgers <hwstar@...>
Subject: Re: [rtpDir] Re: new to the project - questions
Yes, that is the usual way to get an IRLP node, but there's now another way as well. Use ACID with chan_irlp using the irlpsetup.sh script, then send $40.00 via Paypal to Dave Cameron with your newly assigned node number in the comments section of the payment, and he'll take care of adding your node number to the PGP public key ring.
Steve
WA6ZFT
On Dec 27 17:19:46 2008: JI1BQW, Kay Ishikawa wrote:
You have to purchase an IRLP board to be assigned a node number and added in the authentiation key ring. Without those, you will not be able to connect to other IRLP nodes or reflectors, even if you install the IRLP software.
73
http://www.irlp.net/guideline-FAQ.html: "IRLP PGP keys are only assigned to users that support IRLP, either by purchasing IRLP hardware or by making a donation to the project. " These guidelines were last revised by David Cameron, VE7LTD (IRLP System Designer) January 28, 2009 acknowledging advancements in other voice over IP (VoIP) systems. (Per: http://www.mail-archive.com/repeater-builder@yahoogroups.com/msg51571.html)
When questioned in November 2006, about Asterisk and Allstarlink, David Cameron, (VE7LTD) IRLP system designer said they are currently not working or supported pieces of IRLP, although they may be in the future. It seems that that migrating IRLP to an Asterisk based platform will be pushed by the obsolesce of the PC's parallel port. Asterisk code has been developed for USB sound "pocket"/ fob sound devices based on the CM108 chipset for inexpensive do-it-your-self radio interfaces as well as enhanced commercial manufacture of them. The realization of a need for an IRLP redesign in the future, is probably what prompted the change in IRLP guidelines and acknowledgement of advancements in other voice over IP (VoIP) systems.
Another issue is that the binaries that talk to his IRLP hardware board are not open source.
IRLP system designer David Cameron, VE3LTD had developed a similar (commercial) system to IRLP that is being used commercially, and this to may be part of his proprietary design reasoning http://www.roip.com/ The hardware (the radio interface card) is the same as the amateur product. The software is somewhat different but definitely is not free.
Another reason the board design is unpublished is that the board is the IRLP designers only source of funding to keep things alive. Also to cut down on the number of questions/problems from the non-technical savvy. While neither of these are bad, it still doesn't let technical savvy people do much more with. This closed architecture doesn't seem to be in the true spirit of amateur radio if you ask me. The system architecture is simple and powerful. One can have a lot of fun and learn a lot in the process by playing with it.
However, Adi Linden, VA3SLT and others have taken the code that Dave Cameron released and built upon it for a home brew repeater controller. The code Adi produced remains open source and is available here. (An updated version here.) The code still lacks considerable documentation and proper acknowledgment of its origin and contributors. All the features one would expect to find in a repeater controller are supported:
If you wish to use IRLP with a different open interface such as the VA3TO, WB2REM, G3VFP, G4CDY,...Rigblasters, MFJ, SignalLink, etc. (as many of these interfaces have schematics readily available.) The following two open projects have the code necessary to talk to interface IRLP to other hardware interfaces. The rtpdir bridge - to bridge EchoLink IRLP and Asterisk. And thelinkbox also supporting USB sound FOB interfaces.
Imagine how smoothly and fast things would have unfolded if everything was open source, and no one had to waste time reverse engineering other peoples secrets. Isn't that what amateur radio is supposed to be about, working together?
(*Note IRLP & ROIP are not registered trademarks per the Trademark Electronic Search System (TESS). But both are developments of David Cameron, VE3LTD. Echolink is a trademark of Synergenics, LLC., and Asterisk is a trademark of Digium.)