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Homebrew USB Keyer?
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by KG4DGF on October 28, 2009
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I have been practicing CW for a while, and would like to hone my skills with a contest. I would also prefer to use a program, probably N1MM, to key for me as well as do my logging. Unfortunately I do not have a computer with a serial port, only USB ports. I am a little hesitant to use a USB to serial since i have heard of issues and ports are not my specialty.
So I was wondering if anyone knew a homebrew interface that would allow me to key CW while using N1MM via the USB port. I have seen commercial ones, but really do not have the money to shell out right now. I have heard of MCW via the soundcard and Upper Sideband, but really would prefer to have the system function in CW mode (radio is a 706 so i cannot access my 250Hz filter in SSB.
Any help would be appreciated.
73 de WI3M
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RE: Homebrew USB Keyer?
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by VA7CPC on October 28, 2009
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I've used the K1EL USB WinKeyer. It's not cheap ($68 for the kit), but it's really, really good for what you want to do.
It takes the job of generating "on/off" voltages away from the PC. So Windows delays have no effect on its generated code.
Charles
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RE: Homebrew USB Keyer?
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by VA7CPC on October 28, 2009
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Tell your IC-706 that you have a _narrow SSB_ filter installed, rather than a CW filter. [I forget the filter type, but you can look it up in the manual.]
You'll still be able to use the filter for CW by selecting the "NARROW" filter menu item. It will also work (with some offset from its center frequency) in SSB mode with the "NARROW" filter menu item.
This is a well-known kludge in the IC-706 community. It's great for doing PSK31 and RTTY.
Charles
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RE: Homebrew USB Keyer?
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by N3OX on October 28, 2009
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"So I was wondering if anyone knew a homebrew interface that would allow me to key CW while using N1MM via the USB port. I have seen commercial ones,"
I haven't tried using any of mine for CW keying yet, but anything that uses the FTDI FT232RL USB to TTL (0 and 5 volt) serial chip has worked flawlessly here for me in USB/Serial conversion.
Here's a little USB board with one on it:
http://www.sparkfun.com/commerce/product_info.php?products_id=718
If I get a chance this weekend, I think I might have a spare around here somewhere and will give it a try. I can't promise a timetable but I do eventually want to be able to key CW from my computer (mostly so I can do CW by internet remote)
I bet it works.
73
Dan
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RE: Homebrew USB Keyer?
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by N3OX on November 1, 2009
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I tried my spare FT232RL USB <-> Serial converter and configured N1MM to use that, and it sends CW just fine.
I'll probably buy another one to hook up to the radio (this one is for programming some microcontroller boards).
I think the link I posted above should work.
There might be one minor snag.
It seems like they're shipping that board with the output voltage set for 3.3V logic levels. I think most radios these days are 5V.
3.3V is probably above the threshold logic level to read "high" on the CW port but I'm not absolutely sure of that.
I've got my device I/O pins tied to the USB bus voltage for I/O which is 5V... it keys my radio just fine. 3.3V might but I'm not sure. There are a couple of ways around that. If you don't mind some small soldering on a surface mount board, I think you can switch the board over to 5V by un-soldering a solder bridge and finding 5V (it's one of the USB pins and you can tap off the chip side of the resettable fuse I guess)
Another thing you could do is add a couple of NPN transistors hooked up in the right way to give you an "open collector" output:
http://n3ox.net/files/CW_FTDI_3V3_lvlconv.jpg
N1MM holds the DTR pin at a "high" level when you're not sending CW.
So it forward biases the base-emitter junction of Q1, turning it "ON"
Since Q1 is on, Q1 holds the base of Q2 low, which means Q2 is "off" and presents a high impedance to whatever is connected to its collector. So the rig is not keyed.
When N1MM pulls the DTR line low (for a dit or dah), Q1 turns "off", allowing the resistors to pull the base of Q2 up enough to turn Q2 "on," pulling the rig line low and keying the rig.
A nice improvement to this for radio keying is to replace Q2 with an optoisolator, that is use the collector voltage on Q1 to turn on and off the LED inside an optoisolator and use photo transistor in the opto-isolator to key the rig.
I think I'm going to do that anyway.
http://n3ox.net/files/CW_FTDI_3V3_optoconv.jpg
Again, it may be that this just works without extra circuitry but the optoisolator is a nice way to prevent ground loops, etc.
The 2kOhm total between 3.3V and ground might be a little bit big for turning on an optoisolator from 3.3V (you'd have to look at your optoisolator's data sheet to know for sure) so you might want to replace some resistors with somewhat lower values. They're not very critical. You need good voltage levels to drive all the transistors into saturation but that's easy to do with small general purpose NPN transistors. The optoisolator as drawn will only have about 1mA going through the LED so that might be a tad low to key the rig...
73
Dan
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