I have a simple com port interface to key my rig, consisting of the RTS
line passing through a 1K resistor to the base of a 2N2222 transistor
which keys the rig. This works FB, only theoretically it would be nicer
to have the computer and rig grounds isolated. Thus I set out to build
a new interface (and maybe several for some friends) using
optoisolators. I found a huge list of such interfaces at
www.packetradio.com, including one specifically suggested for the
1000MP. These can actually be purchased at a reasonable price as a kit,
but the info is there to make your own.
I set up a breadboard so I could try various configurations and optos.
The 4N25 suggested on that web site didn't work for me (single
transistor opto). I have since tried 2 other optos, both Darlington
pairs (4N29 and 4N33). Using either one of the Darlington optos, keying
the RTS line with software produces a collector current on the order of
10 mA, but the rig doesn't key. I'm using the same cable to the RTTY
connector that works in my single 2N2222 circuit, so I know it's not
some other vagary of the cable/DIN etc.
If I put an ampmeter across the PTT-GND, I measure something on the
order of 10 mA. I have a crummy little VOM... If I put it on the 10 mA
scale, the meter pegs, but the rig does not key. If I put the meter on
the 250 mA scale, it measures about 10 mA, and the rig DOES key.
The opto circuits behave similarly - I measure about 10 mA of collector
current, but the rig doesn't key. I think AA6TY measured the current
between PTT-GND and got something a little higher, e.g. 15-20 mA. Does
anyone use one of these optos for their switch, and/or does anyone have
a technical manual or measured current between PTT-GND??
The specs for all of these and other optos can be found at
http://www.isocomoptocouplers.com/isocom/webparts.htm
SRI bandwidth, but I think this subject is of interest to many on all 3
reflectors. Thanks - 73
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I haven't lost my mind - it's backed up on disk somewhere!
WA9ALS - John
rig: MARK-V FT-1000MP http://www.yaesu.com/markv.html
email: jfleming@shelbynet.net
homepage: http://www.qsl.net/wa9als (now with Shack Cam!)
logbook: http://www.qsl.net/wa9als/search.htm
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