[Premium-Rx] Design Assistance Sought

[Gary Geissinger]

Keith,

What you are describing is a pretty straight-forward problem.  Usually folks use an optical encoder for tuning, then add some sort of controls to set the tuning speed or the digits to be changed.  

I did this for controlling my RF-550 preselector and my WJ-8712 receiver.  Back then the key was to get into the software world as quickly as possible.  Given microcontrollers usually have a large number of I/O pins all that needed to be added were line drivers/ buffers to drive the external device and a few parts to deal with the inputs from the encoder and switches.  The rest would be code.  I'd say not much electrical engineering with most everything being embedded software.  I used a combination of ANSI C and assembly language. For my tuner interface I used 7406 hex open collector drivers for the 22 tuning lines.  The switches and encoders simply needed 10K pull-up resistors or you can program the I/O pins on the microcontroller to have pull-ups.  As you say a Raspberry Pi could be a good answer; I liked the Freescale 9S12C32 family and the boards made by Technological Arts in Canada.  I used a laptop as a controller and display with the 9S12, but you already have a nice front panel on the RF-550.

Alternatively you could solve your problem using digital logic and no microcontroller or processor.  The classic approach would be to have BCD up/down counter chips driven by the encoder.  The parallel outputs of the counter chips would drive the parallel input to the receiver.  There are some simple circuits for conditioning incremental position encoder outputs.  While this would work, today if I used digital logic for the entire design a field programmable gate array would be easier than discrete logic.  You would still need the line drivers to talk to the radio.  Look at the AGLN-NANO-KIT sold by Digikey.  The development environment is available at no cost.  VHDL is not that hard to learn.

The project you are looking at could be a lot of fun.  Probably not worth paying someone to design the hardware if you are willing to dig into the software yourself.

Good Luck and Have Fun,

Gary WA0SPM

Gary A. Geissinger
Chief Electrical Engineer, DigitalGlobe Incorporated

-----Original Message-----
From: premium-rx-bounces at mailman.qth.net [mailto:premium-rx-bounces at mailman.qth.net] On Behalf Of Keith Densmore
Sent: Monday, September 11, 2017 1:20 PM
To: PremiumRX <Premium-Rx at mailman.qth.net>
Subject: [Premium-Rx] Design Assistance Sought

Good Day All,

There are a lot of smart people on this list so I am going to throw out this inquiry here first.

I have a beautiful Harris RF-550 receiver. These rigs use up down switches for tuning  (6 switches in total, one for each decade).

I would like to add the option of rotary tuning  using an encoder.  The radio supports external tuning, it conveniently has a 36 pin Centronics connector on the back which is designed to bring in 22 BCD lines (4 for each decade, but only two needed for 10 MHZ selection. It expects TTL level positive (5 Volts). Each 4 liine BCD can encode the 0-9 needed for that decade.

The problem is I am digitally design challenged, to say the least.  I am open to any way of doing this from CMOS chips through a Raspberry PI, to a dedicated laptop controlling it.  But I need someone to design it.  I'll bet  one of you retired EE's or digital gurus could do it in your sleep. I can build a circuit once I have the schematic.

I'd be glad to pay for the design work, maybe not at commercial rates , but certainly at a reasonable rate. Perhaps you know of something that already exists that could be modified to use.

If you think  you can help, have any ideas or suggestions  please email me.
Hoping to hear from you.

Keith ve3ts/ve3gem
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