Saturday, November 8, 2008

Casing Up the RockMite

My RockMite 20 is safely ensconced in its Leatherman box today. I know the typical enclosure is an Altoids tin, but I've had the Leatherman tin sitting in a closet since last Christmas just waiting to be used for something. It saved me the cost of a box of Altoids and gave me plenty of room to work with. The extra room was nice since this is my first enclosure project in about fifteen years.

The extra space in the box also gave me plenty of room to install my KD0FNR/Panasonic iambic keyer, and the large lid makes for a nice hand rest while keying, more on that later. If you remember from last time, rather than going out and purchasing a keyer, I went with the quick fix of snapping a few switches off an old TV I recently took apart. One of my favorite sayings is 'I'd rather be lucky than smart.' When I tried to snap two switches off the TV's control panel, I came up with three instead. As usual I lucked out! I hadn't been thinking about the mode switch for the radio and I had planned on installing it into the case separately. Since the three TV switches all shared a common ground and were nicely packaged, I put the original mode switch back into storage and wired all three of the RockMite's switches, dot, dash, and mode into the TV control panel.



The RockMite sports an audio user interface. When you briefly click the mode button, you hear three short dots. After that, you can speed up the iambic keyer by clicking the dot button, or slow it down by clicking the dash button. All this control with out an LCD! Sweet!

I didn't want to stress the switch unit any more than I already had when I broke it apart to get the three switches. So, instead of drilling mounting holes in it, I decided to glue it into the enclosure. I drilled three small holes into the enclosure spaced for the three switch buttons. I drilled another three holes for quarter inch #4 machine screws. I was fairly certain I couldn't glue the circuit board to metal, so I placed a quarter inch plastic spacer on each of the screws. The idea was to anchor the circuit board by gluing it to the plastic spacers. The first attempt didn't work. The super glue didn't stick at all. Then I noticed that the circuit board had a shiny coating. I took a razor blade, scraped off the coating and tried again. This time, the board stuck right to the spacers with the desired effect.
















The instructions with the radio warn you to drill into the box with a block of wood behind the metal to avoid tearing the metal. Pay attention to the instructions! I didn't and sure enough when I drilled the hole for the BNC connector:


But, once again I lucked out. I had used a drill bit two sizes too small, so I was able to round the edges out using the correctly sized drill bit.

So, with all my holes drilled, and my connectors installed, I placed the RockMite circuit board in the box on top of quarter inch spacers, reconnected the antenna and switches, turned the unit on and heard... well... nothing!

I immediately decided that I must have a complex failure and ran through all the troubleshooting instructions that came with the kit. The instructions are excellent, and all the measurements they recommend can be done with a DC meter! Fortunately for the radio, (not for my troubleshooting efforts), everything came up normal. I kept noticing that if I touched the antenna wire directly to the lead on D1 I got plenty of audio, but otherwise, nothing. Finally, I checked the resistance across the antenna BNC connector and found out it was zero! When I had re-installed the coax to the BNC, I applied too much heat and the metal shield melted through the insulator causing a short. I replaced the little piece of cable and I was back up and running!

One last note about the keyer. It turns out that the TV buttons cycle just as well being pulled straight up as they do being pushed in. With the tree buttons sticking out the front of the box and the large lid, (the box is about 7 x 4 inches), I can rest my hand on top of the box and use my index finger to pull dots and my middle finger to pull dashes!


I hope these notes are helpful to others building the RockMite. I'll keep adding periodic updates on the project.

Oh, and if you want to get a RockMite of your own, you can do it at:
SmallWonderLabs

And if you need to get a ham license to get one of these on the air, you can practice for that here:
Amateur Radio Licensing Practice Tests
Technician, General, Extra


Have fun!
73,
KD0FNR

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