Earlier this week, I decided to put together a circuit to key my transmitter from this laptop. Since I’m using N1MM logging software, I searched the N1MM website and found a simple circuit using a 2n2222 transistor on this page. It looked simple enough, but after wasting more than an hour searching through my junkbox, I gave up.
The next day I went to the local Radio Shaft and bought a 2n3904. It had about the same specs and was a dime cheaper (59 cents vs. 69 cents). Last night, I finally got around to building the silly thiing. Unfortunately, I soldered the transistor in backwards. I must have fried it, because when I pulled it out and wired it correctly, it was partially on even with no voltage on the base. Since I only bought one transistor, and still can’t find the other one I know I have somewhere, I gave up again. What looked to be a pretty simple project was turning into a real pain.
About an hour and a half after going to bed (around 12:30 in the morning), I felt hungry, so I got up and made myself a snack. While I ate, I fired up my web browser and surfed over to All Electronics to see how much a handful of transistors would cost. While browsing, I came upon some 4N25 opto isolators, and it struck me that I may have some of those in my junk box. Not only would that work, it would also provide some isolation between the computer and the rig.
I didn’t have any 4N25s, but I did have some 4N33s. I did a Google search on “4N33” and found not only the data sheet for the part, but also a pointer to a thread on the WriteLog mailling list discussing the kind of circuit I wanted to build. To find the circuit they were discussing, I did a Google search for “4N33 WriteLog” and quickly found the page describing how to do this.
By this time, it was about 2:30 am, but I figured what the heck, I might as well stay up and build it. I pulled out my breadboarding supplies and built it on a little piece of perf board that’s small enough to fit in the DB-25 housing. This time it worked right off! So, now all I need is a contest to use the thing. Unfortunately, I don’t think I’ll be operating the CW SS next weekend as a friend and I are supposed to be going to the Holland hamfest. If that falls through, however, I’ll be all set to operate it with the N1MM software and my keying circuit.
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