During Field Day this year, I discovered a "weakness" in my equipment. The only way I had to verify that my electronic touch-paddles were operating was to actually key my transmitter. The transmitter is battery operated, and needlessly transmitting wastes that battery. Not a good idea. I needed a keyer!
I had a keyer IC (PKBasic from Jackson Harbor Press) that I purchased years ago to put in my Keyboard Keyer, but with the advent of logging programs that output CW on the serial port of computers, I hadn't used the keyboard keyer in years. As a happy coincidence, the PKBasic runs off 3V, making it ideal for portable operation!
The keyer I made is mainly a support package for the IC, but it adds some features that are fairly important to me...switchable Sidetone, an output "Tune" switch, and Output Isolation using an opto-isolator. The tune switch allows me to constantly key my transmitter for testing SWR; something the transmitter can only do by going deeply into its menu structure.
Since I wanted this to be as rugged as possible, I also wanted all parts and controls to be mounted directly to the PCB...no wires. Typically, battery connections MUST be wires, but in this case, using a 3V battery allowed me to use a coin-cell and mount its holder directly to the PCB. Thus, other than the Piezo which had to be mounted away from its pads, every component is board-mounted directly (and the Piezo is supported by the block shown below).
I'm particularly proud of a couple of aspects of the assembly that I discovered and implemented:
I have built one other chassis of plastic, the container for my portable battery pack, but that was nowhere near as inventive as this. as the picture shows, I added "rails" to slide the PCB into the chassis, and added plastic tubes that are sized just perfectly to screw number 4 screws into snugly...as good as using tapped holes. These two additions made this chassis better even than metal for this application. Once I fused the seams properly, this chassis became quite strong.
-Plasti-Dip as paint
Plasti-dip a rubberized goop that is designed to cover tool handles for improved grip. I used it to "paint" this chassis! I could have used any color paint I wanted, but decided to plasti-dip this chassis for 2 reasons: the plasti-dip provides some shock absorption if I drop the device. It doesn't offer much, but any is better than none. Then, it also encapsulates the chassis. I hope that the encapsulation provides some mechanical strength that glue alone doesn't. I haven't used plastic chassis construction much before and don't fully trust it yet. I hope the plasti-dip encapsulation will make up for any failings of a glued sheet-plastic chassis.
You'll note the plastic block under the piezo speaker. When resting on the PCB, the speaker was far from the holes that allow me to hear it. I needed a way to make the speaker rest higher than the surface of the board. Thus, this block. I stacked 3 pieces of 1/2" by 1/2" plastic and glued them together. I drilled holes for the leads, and the bottom layer has slots cut to direct the leads to the solder holes beside where the speaker actually mounts.
As I mentioned above, I had to build a plastic block on which to rest the piezo; I needed it nearer the holes on the chassis. This picture shows the construction and mounting of that block