OPC-478 V8000 programming cable via MAX233 - HOWTO

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[ yes, there are links to pictures :^) ]

folks,

many of you know that the Icom OPC-478 cable needed to program the Icom V8000 using a PC is quite expensive, ranging from $39 to $49 or so.  (i would like to point out the irony that the programming cable is priced at 1/4 of the retail of the entire V8000 transceiver.  i imagine Icom makes more profit margin on the cable than the transceiver.)

i built an OPC-478 cable substitute today and i just wanted to post a few details for the next guy to go down this road.  there are quite a few DIY designs floating around, with several variants.  some use discrete transistors and other use RS232 level translator IC's, for example the max232 and max 233.  i wanted to try the max233 approach because, well, i thought it to be the most elegant and it had the fewest parts of all the designs i found on the 'net. :*)

the basic schematic i used is the following, with one errata which i will explain a bit later:
http://www.zorg.org/radio/max233md.gif

as you can see there are a minimum of parts.

step 1, procuring the parts:
the hardest is the max233. you can use a max232, however the max232 requires external capacitors for the 10v/-10v charge pumps. the max233 has internal charge pump capacitors, and thus requires 4 fewer parts than an equivalent max232 design. the max233 doesn't appear, however, on the hooks at radio shack nor anyplace else that i've looked.

fortunately, Maxim will send you 2 FREE samples of any parts you want, including the max233 -- that's one more than you need. just go to
http://www.maxim-ic.com/quick_view2.cfm?pdf_num=1798
and scroll down to where it says "Request Samples". specifically
http://www.maxim-ic.com/samplescart.cfm?Action=Add&PartNo=MAX233

you'll have to fill out a form with your name and address etc, but it's all very simple. for the questions regarding the intended use, just put down "Education" or "Research". your parts will arrive in about 3 days via the USPS -- it could not be simpler. make sure that you specify the EXACT package that you want; i find the DIP parts easier to use when doing projects like this. otherwise you may end up getting the SOIC package and that will require the use of a magnifying glass. (i should point out that you would do well to "sample" any other maxim/dallas parts you are interested in. it's always handy to have an extra max232 laying around, plus the odd adjustable voltage regulator). you can of course also order devices directly from maxim, using the shopping cart application on their web page.

for the rest of the parts, radio shack has them. i really only needed to get the 5.1V zener (radio shack cat# 276-565 / 1N4733A) as i had everything else in my parts bin.  but i also picked up a PCB-mounted 1/8" stereo jack, and a 6' long 1/8" stereo patch cable (w/ plugs on both ends). total outlay was around US$9. this is on the high end, if you don't construct it like i did you can come away for about half that. i wanted the patch cable so i could directly clone a pair of V8000's as well. if you make up the patch cable yourself, using connectors from radio shack and some spare wire, it comes out more expensive than just buying the patch cable outright.

step 2, construction:
i used a small piece of perfboard to mount everything onto, along with a DB9 on the end of a ribbon cable leftoever from a prior project. see these pictures of my setup:
http://losdos.dyndns.org:8080/public/icom-v8000/

as you can see, all of the components mount topside, with point to point wiring on the bottom. i employed a 20 pin socket to wire to, then inserted the max233 after everything was tested. speaking of, after completing the soldering, first check for a power to ground short. then, plug the adapter into your COM port and measure that the +5V rail is correct. this voltage *may* only appear when the icom SW is running and trying to talk to the radio, as the adpater requires that DTR and CTS are asserted (+10v). otherwise, you may notice no voltage. now unplug the adapter and insert the max233.

step 3, testing:
my enthusiasm for the max233 design dropped significantly when it initially didn't work. i checked and rechecked my wiring, buzzed out all of the connections from the DB9, and so on. initially i suspected the RS232 (PC) side of the max233, but my voltmeter confirmed everything was as it should be. i noticed a few things about the TTL (radio) side. namely, my logic analyzer told me that data was going from the PC to the radio when i hit the "Connect" button on Icom's software. but for some reason, the radio was evinently not responding. i thought perhaps that my (new) radio had a defective port, or the cable that i purchased at radio shack was defective. however, by disconnecting the radio from the adapter, and just plugging the cable into the radio, i could run a simple test. go into clone mode (see your users manual) and initiate a "clone out". the radio will send data out the port, regardless of whether it is connected to anything. low and behold, my logic analyzer (connected with clip leads to the far end of the unterminated patch cable) captured the pulses. so the cable and radio were both good.

i began to wonder if there wasn't a contention problem on the TTL end. the Icom "1 wire bus" connection requires that each end alternate relinquishing the "bus" so that the other end can talk. indeed, a little more inspection showed that the max233 TTL output driver was holding the bus high when the radio wanted to speak to the PC. this is easily solved by introducing a diode (another 1N4148 or 1N914) into the schematic, as shown below:
http://losdos.dyndns.org:8080/public/icom-v8000/opc478-via-max233-mod1_sm.jpg

with this new diode in place, the circuit worked perfectly. i'm not sure whether the omission of this diode is due to my new vintage radio, or an oversight with the schematic i found on the web, or the original schematic just happened to work for the original author. but nevertheless, the published max233 circuit used in conjunction with my "diode mod" works 100% with my brand new V8000.

step 3, finishing up:
my original plan was to just take a 1" dia piece of heat shrink tubing and "enclose" my adapter. i'm not going for any awards for looks here -- i just want to prevent any possibility of shorts between the adapter and whetever it is sitting on. but then i noticed that just by serendipity, the little clear plastic box that maxim sent my max233's in is just the right size for the adapter. so i'm going to drill a hole for the 1/8" jack, and provide a cut-out for the ribbon cable. simple, no cost, and my pics will make a nice "thank you" to maxim as well.

i hope all that info helps somebody looking for an opc-478 substitute.

jim / n2mpt

ps, some relevant info
http://pdfserv.maxim-ic.com/en/ds/MAX220-MAX249.pdf
http://www.qsl.net/vk3jeg/opc-478.html
http://www.qsl.net/kc8unj/
http://www.qsl.net/kc8unj/CATbox%20WSARC.pdf (see page 19)
http://www.westsomerset-arc.co.uk/VX-5%20&%207R%20Interface.pdf

Alan Applegate:
Why didn't you post this as an article replete with pictures?

Alan, KØBG
www.k0bg.com

:
alan,

i appreciate your comment, but i don't appreciate your delivery.  so i'll just say "i'm new here" and then ask "what differentiates your definition of an 'article' from what i just posted?"  

if it's my capitalization that's grinding you, well i've been programming in C for far too long.  as for the pictures, i'm assuming you missed the link about halfway down my writeup.

73,
jim / n2mpt

ps
re:  http://www.k0bg.com/fuses.html
your information on DC breakers ("DC breakers are almost exclusively thermal") is somewhat misleading.  a majority of the high quality DC breakers used for telecom and aviation applications use a dual magnetic + thermal actuation system.  unlike your assertion, they can be purchased in a variety of delay curve configurations -- from fast trip to surge tolerant.  consult the datasheets from vendors such as Airpax, ETA, P&B, Eaton/Heinemann, and Carlingswitch.  this message arrives to you via routing and telecom equipment protected by a number of DC breakers.

Stuart Blake Tener:
Jim:

This is a very interesting design, and I am curious about some several things concerning it.

I just ordered a Mac (PowerBook G4, 17"), and am contemplating to use Virtual PC to run Windows so I can continue using some legacy applications like the W32A software until such time as a Unix version of the W32A software will be available or written. Virtual PC will present most any hardware port from the Mac to Windows.

(a) How difficult would it be to modify this design such that it worked via USB port (using say a MAX3454E, so both USB 1 and USB2.0 could be supported), since the new MAC laptop I am getting has no serial ports, and is only sold with USB ports. I know I can add a USB-serial cable and use your original design, but thats not so elegant!

(b) Do you know if your design would function with an ICOM W32A HT?

(c) Though pin 14 on the MAX233 is depicted in your diagram in reference (1), it seems not to be connected to anything, is this a proper reading of the schematic?

(d) With regard to the diagram as depicted in reference (1), and given a W32A, would the GND & RING connections be the same with a W32A?

Reference 1: http://www.zorg.org/radio/max233md.gif

Stuart, N3GWG
Beverly Hills, CA

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stuart,

(a) How difficult would it be to modify this design such that it worked via USB port (using say a MAX3454E, so both USB 1 and USB2.0 could be supported), since the new MAC laptop I am getting has no serial ports, and is only sold with USB ports. I know I can add a USB-serial cable and use your original design, but thats not so elegant!

i see where you are going but this is a difficult call.  the "emulated" HW and SW food chain on your new Mac has to mimic very closely the original implementation; introducing USB into the equation along with additional hardware and the abstraction layer of Virtual PC may make things complicated.  if i were you i'd run the ball up the middle on this one and get a USB-serial adapter dongle.  i use one and indeed it works fine with the Icom programming software (from WinXP, not in an emulated environ though).  

aside, i have been thinking about designing a PIC-based OPC478-like adapter for native USB.  i've done a lot of PIC projects of various sizes but have not had the opportunity and motive to do a USB implementation yet.  the problem for me is that i look at the USB-serial adapter dongle designs and if you simply remove (or bypass) the level translator at the serial side you have effectively got yourself a USB-based OPC478.  so why should i design a PIC-based one?  :*)  the ubiquitous serial USB dongles are cheaper than an OPC478, so that i think is the next OPC478 lookalike "hack", esp useful for folks like yourself w/o COM ports.  

(b) Do you know if your design would function with an ICOM W32A HT?

i'm not familiar with the W32A HT but if it uses the OPC-478 as it's programming cable, then this alternative design *should* in fact work.

(c) Though pin 14 on the MAX233 is depicted in your diagram in reference (1), it seems not to be connected to anything, is this a proper reading of the schematic?

that is correct, pin 14 is NC.

(d) With regard to the diagram as depicted in reference (1), and given a W32A, would the GND & RING connections be the same with a W32A?

again, not being familiar with the W32A, i'd suggest that you take a look at the manual and determine what the tip, ring, and ground actually connect to.  i assume that, like the V8000, all of the connectivity is on one jack which is shared for the external speaker and the data connection.  if you can post a link to the  W32A pinout or schematic it can be easily grok'd to figure out the right connections.

best regards,
jim n2mpt
 

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