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Author Topic: OPC-478 V8000 programming cable via MAX233 - HOWTO  (Read 8146 times)
KD7MMJ
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« Reply #15 on: April 14, 2009, 12:08:36 PM »

I don't understand how, with the diode mod, the MAX233 is able to output to the transceiver tx/rx buss. It would appear that the diode, while preventing the buss from being held high, would also block the output TTL pulses. Am I missing something?
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K0BG
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« Reply #16 on: April 14, 2009, 05:30:27 PM »

No one was trying to be short with you Jim, but this post merited posting as an article. Perhaps you should still do so, as the 'technique' can be applied to a bunch of radios, not just the 8000.

As for the circuit breakers: My biggest problem with circuit breakers is simply that the current break rating isn't anywhere near that of a fuse. This is true, no matter what kind of breaker you choose.

If you dead short a decent SLI battery, or especially an AGM one, the current surge can easily exceed 3,000 amps. While there are breakers rated for such overloads, they are the exception, not the rule.

I will also agree that there are some breakers with very fast trip times. However, under the exact load, with the exact same breaker/fuse rating, the hysteresis of the breaker will much longer than that of the fuse. How much longer is the question, and that depend on the type.


Alan, KØBG
www.k0bg.com
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N3GWG
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Posts: 21




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« Reply #17 on: April 14, 2009, 06:45:20 PM »

Dear Sir:

Good grief olde boy, you make it seem as if these cables are not $2.99...oh wait, but they are $2.99!

At least if you type in "OPC-478" in eBay they are, now that is of course for a USB style cable. If you insist on a DB-9 style of serial programming cable then you are going to be forced to pay less and spend a $1.49 for the cable.

I mean after all, if it takes you 30 minutes to make the cable, so, your time must be worth what, $3/hr? Smiley


Stuart
N3GWG
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N2MPT
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« Reply #18 on: April 14, 2009, 07:55:03 PM »


"I don't understand how, with the diode mod, the MAX233 is able to output to the transceiver tx/rx buss. It would appear that the diode, while preventing the buss from being held high, would also block the output TTL pulses. Am I missing something?"

the result of adding the diode is that the output of the MAX233 only pulls down the line.  the line is pulled high by a weak pull-up resistor internal to the radio.  

ps:
thank you for asking an intelligent question.

jim / n2mpt

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N2MPT
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« Reply #19 on: April 14, 2009, 08:03:50 PM »


alan,

"No one was trying to be short with you Jim, but this post merited posting as an article. Perhaps you should still do so, as the 'technique' can be applied to a bunch of radios, not just the 8000."

i'll take your advice under consideration, namely pointing out what should have been done 5 years ago before the Eham article format even existed.

"As for the circuit breakers: My biggest problem with circuit breakers is simply that the current break rating isn't anywhere near that of a fuse. This is true, no matter what kind of breaker you choose."

oh really?

so the Airpax series IEG breakers i'm using don't?  i believe i pointed this out earlier in this thread -- namely that if you understand the problem in it's entirety, read the datasheets carefully, and select the proper components for the application, all is well.  some of us take this approach.  others, not so much.

"If you dead short a decent SLI battery, or especially an AGM one, the current surge can easily exceed 3,000 amps. "

the Airpax series IEG breakers i'm using are 2.5X that.

"I will also agree that there are some breakers with very fast trip times. However, under the exact load, with the exact same breaker/fuse rating, the hysteresis of the breaker will much longer than that of the fuse. How much longer is the question, and that depend on the type."

this must be why the entirety of the avionics, maritime, and telecommunications industries have standardized on fuses for power applications, right?  oh, wait...

jim / n2mpt

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N2MPT
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« Reply #20 on: April 14, 2009, 08:08:18 PM »


"Good grief olde boy, you make it seem as if these cables are not $2.99...oh wait, but they are $2.99!
At least if you type in "OPC-478" in eBay they are, now that is of course for a USB style cable. If you insist on a DB-9 style of serial programming cable then you are going to be forced to pay less and spend a $1.49 for the cable. "

#1: i am truly sorry i wasted my own time attempting to help you with your prior posts above.

#2: in 2004, when i authored this post, there was no OPC478 substitute available on Ebay.  next i suppose you will find a ancient post regarding $500 PC memory DIMMS and point out that they are now just $5.

jim / n2mpt

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K0BG
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« Reply #21 on: April 15, 2009, 06:56:47 AM »

I looked up the high current interrupt rating of a IEG series. The max rating is 4,000 amps. This is not 2.5 times 3,000 amps. More telltale are the trip times under load (hysteresis curve).

The real bottom line is certainly one of cost in the minds of most amateurs. There are some folks who don't mind paying $50+ for a breaker. Some folks don't mind paying the tariff when using them as an on/off switch in places where one isn't needed in the first place. But that isn't me.

Alan, KØBG
www.k0bg.com
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KJ4RWH
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« Reply #22 on: October 23, 2014, 11:23:41 AM »

Thanks for the time & effort for the complete work up on the V8000 interface cable. Jeff KJ4RWH
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