Additional Digital Outputs for the Link RLC-4 Repeater Controller

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Back to Home Additional Digital Outputs for the Link RLC-4 Repeater Controller
By Brad Andrews KB9BPF
29 December 2007

For several years the K9MCE Macoupin County Radio Club 146.865 repeater has been using a Link RLC-4 Controller. Recent upgrades to our system, including voter control and ability to enable and disable PL encoders and decoders on the various controller and voter ports, required more digital output control lines than are included on the stock RLC-4. The RLC-4 V1.79 manual offers a solution to this problem: expanded outputs using outboard shift registers.

(By the way, the hardware modification needed to make the remote receiver point-to-point link audio sound good is described on the Hamtronics page at this web site, and an article will be forthcoming which will describe my modification to the WB2WHC voter, allowing it to be controlled by logic signals from the controller.)

I read the Link RLC-4 book and studied materials on the Link web site in order to discern how the RLC-4 expects the external shift register circuitry to work. I built the circuit and verified that the latch logic sense, etc. at the RLC-4 outputs is correct for the 4094 shift registers with no inverters or gating.

Some tips to others, things to keep in mind about this, collected for future reference:

To cascade 4094s for more than eight outputs, the Q output (as opposed to the NOT-Q or Q-Prime output), is the one to feed to the next register's data input. Perhaps I was just dense that day, but it wasn't immediately obvious to me from the data sheet. Finding the bcd.pdf schematic on the Link website made that one easy.
The RLC-4 outputs, being open-collector types, need pull-up resistors. Some folks have had better luck with 10K pull-ups (as oposed to 100k). I used 10K and still had trouble. I'm sure it was because I was using a longish (10 foot) DB25S to DB25P cable so there was a lot of capacitance, besides the 0.001uF RF bypass caps I used on the shift register board. Switching to 1K pull-ups made it work reliably. Ultimately I went to 100pF RF bypass caps and 2.2K pull-ups, which is not noted on the schematic.
When an extended output is ON, the shift register output is HIGH, unlike the RLC-4's open- collector outputs which pull LOW when an output is ON. If one were to use the shift register output to drive an inverting open-collector buffer/driver such as the ULN2803A, the outputs would behave just like the original RLC-4 logical outputs.
In case anyone else needs to implement extended outputs on their RLC-4, or other compatible controller but doesn't feel up to breadboarding, you can download my ExpressPCB files (see below), ready for submission to them.

Here is a synopsis of the circuit:

Three 4094s for a total of 24 outputs
Set up for inclusion of RF bypass caps on all I/Os.
The RLC-4 connection is through a 26-pin header, which is laid out for use with ribbon cable and an IDC-type D25P connector.
In addition, the rest of the D25P connection to the RLC-4 is broken out to a 10-pin connector for easy use of the Analog and Logical inputs.
An expansion port is provided in order to cascade boards for more outputs, as well as providing access to the RLC-4's remaining normal open-collector Logical Output 4.
The extended outputs are broken into three banks of eight. +V and GND are also available on each 10-pin connector.

To cascade these boards for more outputs:

Connect STR (the strobe signal) on the expansion port (J02-2) of the first board (the one connected to the RLC-4) to OUT1/STR (J01-13) of the next shift register board.
Connect CLK (J02-3) (the clock signal) of the first board to OUT2/CLK (J01-12) of the next board.
Connect DAT3 (J02-4) (the data signal) of the first board to OUT3/DATA (J01-11) of the next board.
Connect a third board to the second board in a similar fashion. Add 24 to the indicated output number for the second board. Add 48 to the indicated output number for the third board.

RLC-4 Extended Output commands: (Refer to V1.79 documentation pages 12-19 for more info.)
Note that in the commands below the xx is the two-digit output number with a leading zero if necessary, i.e. 01 or 24.

To enable RLC-4 Extended Outputs: N 096 1
To disable RLC-4 Extended Outputs: N 096 0
To recall extended output ON or OFF state: N 096 xx
To turn extended output ON (output goes high): N 096 xx 1
To turn extended output OFF (output goes LOW): N 096 xx 0

Click on the images below to enlarge them:

Front of board
Rear of board

Board layout

Schematic sheet one
Schematic sheet two

Click on the links below for rotated versions of the above files (oriented for printing). These are large files, you may want to select the "Fit to page" option in your printer properties when printing.

Click on the links below For the Express PCB files:

The .PCB file 50Kb
The .SCH file 37Kb

Acknowledgements and Credits:

The schematic was developed from the information in the Link manuals and from information on the Link web site.
I desired a professional-quality result, so I had PC boards made. They were laid out with the free software from ExpressPCB, and the boards were made by them. There is no reason that a perf-board version would not work just as well.

Contact:

Brad Andrews KB9BPF can be contacted at (callsign) //at// arrl //dot// net
(the email address has been disguised in an attempt to thwart the spambots).

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This page originally posted on 18-Mar-2008

This web page, this web site, the information presented in and on its pages and in these modifications and conversions is © Copyrighted 1995 and (date of last update) by Kevin Custer W3KKC and multiple originating authors. All Rights Reserved, including that of paper and web publication elsewhere.