Nuts and Volts - July 2014

are each held in place with three T connections; once tightened, they hold everything in place very well. I am not sure how well it would hold up if I dropped it off the table, but it has a nice solid feel in the hand. The laser machine has the capability of etching onto the wood. This was used to etch in some identification information, as well as the project name. Getting the etch power just right so that the results are nice and dark takes some playing around, but thankfully baltic birch plywood is quite consistent.

There is actually quite a large number of items mounted to the top of this box. We have the on/off switch, a reset switch, three LEDs, a servo motor, and three slots for the T-slot nuts and bolts. I wanted the servo horn to be centered in the design which dictated where a lot of the other items needed to go.

The servo motor is held in place very securely using four nuts and bolts; the power switch and LED bezels are a simple press-fit design. The reset button was the only item on the top of the box that would have been better if I had a panel mount style momentary switch. The switch that I

used is meant to be a replacement switch for computer reset buttons. These switches are snapped into a housing and have a button cap that presses it. It is mounted to the underside of the top panel using some hot glue, and has the switch shaft poking up through the top about 3 mm, which isn’t too bad. Thankfully, the switch throw is only about 2 mm before it activates. The bottom panel doesn’t have any holes cut into it other than four bolt holes for the perfboard to get mounted. Turns out a rectangular perfboard is not that simple to fit into a triangular base since there are mounting screws as well as the power input and alarm output jacks in close quarters. The perfboard is held off the bottom panel using 1/4 inch nylon spacers so that none of the solder connections are in contact with the case. It also allows for just enough space for the lower rear mounting screw to be inserted.

Testing It Out

I tried the project out with the servo disconnected so it wouldn’t alarm the cats during testing. I wanted to see how well the ultrasonic sensors worked with a furry cat compared to the piece of cardboard I was using during testing. It was a bit of an afterthought that there might be a problem since I was just dealing with the sensors as magic boxes. However, in reality, they are sending out a burst of sound (above the human hearing range) and waiting for it to bounce off an object and return. One of our cats looks