[JRC] (More) Construction of RS-232 board for NRD-525

[Brooke Clarke]

Hi Phil:

I'm not sure what the CMH-532 board is, but if it's just a computer interface
then the -12 Volts needed for RS-232 comes from a charge pump that's part of the
MAX-232 type TTL to RS-232 IC.  These chips come in many flavors with different
numbers of converters and with either internal or external charge pump caps.
You might need 4 converters (Tx data, Rx data, RTS and CTS).

Have Fun,

Brooke

Philip Atchley wrote:

> Hello, it's me again.
> After extensively studying the schematic of the CMH-532 board I have come to
> the conclusion that it is entirely feasable to build one of these, or at
> least a board that is functionally identical electrically.   All the chips
> appear to be common garden variety chips (though it is getting more
> difficult to obtain DIP chips, everything's going smt).
>
> The  present plan entails building the basic circuit on R/S Universal IC
> circuit cards (one or two sandwiched as needed) and replacing the DC/DC
> converter with either a commercial -12VDC DC/DC converter chip or a "charge
> pump".  To help with this planning task I've contacted my brother who is
> much stronger in "Digital" than I am (my specialty is RF and analog).   The
> DC/DC converter is the sticky wicket as all the digi stuff is more or less
> routine  circuits.
>
> Depending on what it costs to get that -12VDC I suspect the cost of
> components may well be under $50.00, especially as I have some of the needed
> parts in my junkbox.  But even if a person bought everything new it would be
> WELL under the 300.00 or so I've been told these units often sell for!!!
>
> NOW, I need information from anyone who can help me.  The owners manual
> doesn't give any particulars on BAUD RATE or what commands the NRD-525
> expects over the RS-232 cable, though I expect I could use any of the
> control progrms that are already out there for the radio (including my
> Fineware Shortwave database program).
>
> QUESTIONS:
> 1.  What is the physical size of the card (in case I wish to later add a
> rtty card)?
> 2.  What is the BAUD rate to the computer?
> 3.  What commands are read to and from the radio?
> 4.  What is the "connector type" to the I/O Data Card (looks like just an
> inline header at first glance)?
> 5.  Does the RS-232 cable that exits from the card go directly to the rear
> panel connector or is there another place this cable terminates?
> 6.  What is the Type of rear panel connector (DB-9 ?).
>
> I expect it will probably be a "work in progress" for the next couple months
> but when I finally get a working sample I'll try to post the schematic,
> construction information etc for anyone who may want to build one.  It will
> be labor intensive as it will be "point to point" wired on the universal
> circuit card.  I DON'T intend to make a PC board.
>
> 73 de Phil  KO6BB
>
> *****************************************************
> *  Chasing NDB's (Non-Directional Beacons)with ...  *
> *  RECEIVER 1: JRC NRD-525 W/500Hz CW filter.       *
> *  RECEIVER 2: Homebrew Longwave CW receiver.       *
> *  AUDIO FILTERS: Datong FL-3, Heathkit HD-1418.    *
> *  ANTENNA: Loaded 20 Meter Long Sloper.            *
> *  50dB Gain Low Noise Tunable Preamp.              *
> *  LOCATION: Merced, Central California.            *
> *  COORDINATES: 37.18N  120.29W  CM97sh.            *
> *****************************************************
>
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