A      DTMF   Controlled      ICom     IC-R75  Communications  Receiver .

This is  something I have always had a desire to do  and I did start the project using the old reliable IC  R71  receiver which will run on 13.8 v DC .. Since I was not at all sure of the computer connection for this receiver ,I began to experiment with opto couplers across the  frequency   and mode controls  keypad .  the  optocouplers were to be driven by the  latched output of a DTMF  decoder  . thus I had a scheme to remotely control the receiver  on a solar powered , low  HF noise hilltop location  a long way from the built up area via a  2 m command frequency  and listen to the HF  audio output on 70cms. 
This is the hilltop  farm site of our  local 2m Linear repeater ( whose audio has to be heard to be believed ) and sounds just like a simplex contact  .  The HF noise here at this site is purely atmospheric. We are so far from any houses  there is just no way local man made nearfield noise contaminates the site . Its a perfect site for an HF receiver . 

                 
2M Rx ( blue)   Zares 70cm Transmitter , Basic Stamp                                 Inside W2FS  Controller    (    70 cms audio level pot ~ 47K) 

I also had in the shack an Icom  R75 receiver , which can be driven using an  external computer control via a two  wire system , the rear of the receiver has a 3.5mm mono jack plug for application of the bidirectional data  and  while perving on the net , with great luck  I came across the  article by John Hansen W2FS in QST  for May 1998  titled  " An Inexpensive Remote base station Controller  Using the  Basic Stamphttp://www.coastalchip.com/   This was the answer to my prayer  ....dump the R71 receiver project and press the R75 into operation !. John had written the software to enable a Basic Stamp microprocessor to control  an Icom 706 HF rig remotely  via DTMF  generated on a hand held radio . Download and  Read the Article,  it is very informative  The beauty about the Icom radios  is that all the rigs  use the same basic control commands and what works on a 706 will most probably work on any computer controlled Icom  ...within reason . So I studied up control codes, commands adresses etc  for icom radios ,  There is an extremely informative german website http://plicht.de/ekki/civ/civ-p4301-r75.html   which is a must read for anyone contemplating external control of icom equipment . 

The PC Boards for the project are available ex  stock  from  "Far Circuits" in USA ,     http://www.farcircuits.net/  so I ordered 4 pre etched and drilled PC boards at US$6 each ,plus postage down  under ,  and Fred had them here in no time at all.  Meanwhile I had ordered the Basic Stanp BS2  itself not cheap NZ$ 70 ,  educational programming  kit locally, more $$$  ( which you do not need  for this project as you can program the Stamp via  your RS232 port on your computer  straight into the W2FS  remote base PC Board, )  and sourced the  DTMF decoder  equivalent  ZARLINK   CT8880 IC from a source in Australia .  While  waiting for all these parts I downloaded the  Zipped Stamp  Basic  control program from the "net " source       http://www.arrl.org/files/qst-binaries/              and studied it as closely as I could . also downloading the free programming software from the Parallax website . http://www.parallax.com/tabid/441/Default.aspx

When the parts were all here I assembled the pcboard connected all the audio in , out cables,  required plugs switches sockets  etc ,  I plugged the controller board into the Rs232 port  switched the controller on  and loaded the 706 controller software into the Stamp , connected it all up to the 2m radio ( control frequency)  70 cms radio  my received HF audio   output , IC-706  data connection  and them tried different commands as described in the  QST Article ,  Bingo it  worked on the 706  so I swapped over to the data port on the R75  and bingo that worked as well  ....jackpot!!

We now have the makings of a handheld controlled remote HF receiver   ( the 706 may have been a more versitile unit to place up the hill as it has wide receive  frequency coverage ), however the site is solar powered and the  706 has a couple of undesirable features , like high standing receive current   and it would require  modification to remotely turn it on and off. We dont need to transmit from there as that can be done from home where electrical supply is not limited ,and ambient local noise is not a concern,  
The  original software is written to readout the frequency and modes of the radio if interogated in CW ,This works well, but Im not a cw  man  so I  popped the UT 102 speech synthesiser into the  R-75  so It would speak the frequencies when commanded .   There was some simple basic commands added to the existing code to do this  I "remed" out the morse routine and dropped in the line of basic call subroutine ,  to command the speech synthesiser to read out frequency and operation mode  when the  morse subrountine was called .

speech:
SEROUT 8,813,[$FE,$FE,$48,$E0,$13,$00,$FD]              (' to set speech synthesiser to talk)
RETURN

This did all I really wanted to as far as knowing frequency and modes the receiver was on ,  however there was another extremely useful piece of information I found in the Icom command  codes  !
 The R8500  and R75  radios are the only icom  radios that have a software "on"  and "off " function..... Yahoo!!    I dont have to solder an optocoupler across the "ON-OFF" button to remotely turn the R75 off and  on so I delved into the basic stamp code again and inserted this  line 

'======================MAIN EVENT LOOP===========================
Gateopen:
HIGH 13
GOTO switch
'======================switch r 75 on ======================================

switch:

SEROUT 8,813, [$FE,$FE,$48,$E0,$18,$01,$FD] '       ( turn radio on   !!  )

GOTO main

-----------------------------------------------------------------------------------

"" heaps of lines of code in between here "" 

GOSUB morse
NEXT
RETURN

shutdown:
GOSUB id

SEROUT 8,813,[$FE,$FE,$48,$E0,$18,$00,$FD]       ( turn radio off !!)

GOTO gateway

iddrop:
OUT7 = 1
PAUSE 100
OUT7 = 0
PAUSE 100
OUT7 = 1
GOSUB id
GOTO main

speech:
SEROUT 8,813,[$FE,$FE,$48,$E0,$13,$00,$FD] '   (to set speech synthesiser to talk) 
RETURN
'=======================ROUTINE TO TRANSMIT MORSE=======================
'This routine is based upon Application Note #8 in the Basic Stamp 1
'manual

------------------------------------------------------------------------------

Now I can turn the Receiver off and on remotely !  change frequency, mode have it all read back to me ,,,,,  all with software  !! 
 I dont have to worry too much about  power budget as the  controller unit which draws milliamps , has a time out function  so that if you drop dead using the remote receiver  or your handheld batterries go flat it will turn everything  off after  a user  "defined by software " period of  time  go to standby  and it works a treat


 .                                      
                Icom R-75  in  Repeater shed .  Blue unit is 145 Mhz Receiver,   70 Cms hand held  underneath charge meters 

 Now I am no programmer and the scruffy code i have inserted could no doubt be tidied ,  but it works    you could add all sorts of commands to this code if you wanted to.    I can now drive around in the middle of town  not worrying about the crap sig to noise of the mobile HF transceiver  as i can talk from my Vehicle  to my friends on HF ,   and hear them coming back loud and clear at the remote HF site  via the 70 cm  backlink   and the beauty of the icom 706  in the vehicle is i can have an HF SSB  /  432  NMFB  split to achieve this !! 

What I have found with the system is sometimes the remote command unit must fall over when decoding DTMF  multipath ,  If you find that it is not responding how it should .   just leave the system for 5 mins or so and the stamp will clear itself and continue on as it should ,  Ive not had a situation where I could not get in and obtain control.. 

        
Looking towards Rotorua city  10Kms away                                                                      Looking out  west over lake Rotorua

                                                               we are so far from anywhere it takes 30Mins to get there from town  with 4WD 

                         

               Looking north east out to Maketu  ( sea)                                                             looking   East  out  to Mnt Tarawera

Well  how well does it go ? after putting up the G5RV antenna and connecting it to the receiver and listening on 10 m,  we can hear the low level background  noise eminating from the  little Zares 70 cms  synthesised transceiver ! so thats going to have to be quelled , hopefully a few turns around  ferrite toroids with the antenna coax and power supply  will help minimize  that  . Then when the sun comes out full shine and the SLA batteries are fully charged, the bloody solar panel regulator makes its presence felt  by causing a whine on the received  audio ( PWM  unit)   I think this may be DC power induced as when I switch in  the R 75  preamp on 10m ,  the sig to noise improves but the whine doesnt increase ! ,  need some good DC filtering  me thinks 
. You do however notice the improved signal when compare to my  almost identicle home set up ( G5RV and R-75 Rx  )  on the same signals , my background semi rural location still has a higher local background noise so very  weak signals , readable on the remote site are almost uncopyable on the home set up .     Well at least the guys in town with their very high local noise level on 80  and 40  m will still be able to work some good DX !! 

 

The source code is a ZIP  File   706stamp.zip  and is at http://www.arrl.org/files/qst-binaries/   scroll down near the bottom to find  MAY 1998

Cheers  Mike ZL1BTB

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