Posts Tagged Construction
Katie and I needed to get a dresser/changing table for Emma. We decided to find an antique dresser to redo rather than the pressed-wood pieces of crap you can buy today. We found one at the Corvallis ARC that fit the bill nicely. Unfortunately, I neglected to take photos of it before attacking it with the sander. The following two photos are during the sanding process, though.
The stain and finish that they used was nasty to sand off. When it got hot from the friction, it would melt, kinda, and gum up the sand paper. Eventually, and after many sheets, we got it all off. In the process, I bought a Ryobi Corner Cat which I like O.K. I had to replace the velcro pad that holds the sand paper because it wore out. Shipping took a bit, but the replacements were only a dollar or two.
Once I got all the stain off, I could assess the level of wear the dresser had accumulated over the years. In total, it wasn’t bad. It was pretty interesting to see how construction methods have changes over the years.
In getting ready to paint, I masked off the inside of the chest openings. In this view, you can see the construction. Lots of random sizes of lumber, everything is mortised, etc.
It took a ton of coats to adequately paint the dresser. It didn’t help that we did this at the height of summer, and it was HOT. The paint was practically drying as soon as it left the pail. This left a very poor finish, and honestly, I’m a bit disappointed in it.
Eventually, it got to a point that I could live with, and we reassembled everything. I chucked the knobs into the drill to sand the finish off. I’d like to eventually get some antique porcelain knobs. I think that would look really nice.
One extra thing we had to do, that I don’t have pictures of, is replace the drawer bottoms. Most of them were in really bad shape, and weren’t even square! I just bought some plywood at the store and had my friend Tom cut them to size on his table saw.
We’re all finished! Here’s the dresser in its new home, complete with changing pad. Hopefully, as Emma grows up, she’ll like and appreciate it!
I was able to find some designs online that fit my needs. The major constraint that I had to deal with is the impedance issue. Nearly everything amateur radio related is 50 ohms, and nearly everything video related is 75. The cheap Yagis paper written by Kent Britain, WA5VBJ, has a 75 ohm 421 Mhz antenna intended for amateur television (ATV). My transmitter is 434 Mhz, but I figured it would be close enough. The great thing about these designs is that they can be built using supplies from a standard hardware store. The elements are made from #10 bare copper wire, and the beam is wood.
An interesting characteristic of antennas, and RF in general, is that to get a stronger signal you often have to make compromises. A Yagi works by increasing the directionality to increase the signal. Unfortunately, because my plane is going to be flying around, I can’t be too directional. To get better results, without making things worse, I decided to only use the reflector and “driven element”. By eliminating the “directors” I hope that I can get the best possible results. (If you’re confused by this “director”, “reflector”, and “driven element” gibberish, the best place to look is the wikipedia article. But all that is necessary for this discussion is that the reflector is behind the driven element [which connects to the transmitter or receiver] and reflects the signal forward, and the directors go in front and focus the signal into a narrower beam).
There were some problems during construction that I should mention to help others wanting to try something like this. The antenna designs specify that the feed cable should be soldered directly to the driven element. This should work great on traditional 50 ohm radio cabling, such as LMR or RG-type cables. These cables have copper braid shield around the circumference. With the 75 ohm cable used in video, often made as cheaply as possible, a loose aluminum braid is used as the shield. This is a major problem that I had to deal with. It took me a while to even understand why the braid wasn’t soldering. I think I assumed that the braid was made of tin. After a few hours of searching, I discovered it was aluminum. Aluminum oxide forms almost immediately and can’t be soldered to, so even sanding the wire doesn’t help. There are solder pastes and fluxes that help, but I wasn’t interested in waiting for something to be shipped. My solution, if you want to call it that, was to mechanically attach the braid to some other wire that can be soldered.
In the first image of the post, I’m comparing the new antenna versus the others I used earlier. When the Yagi was installed, I rotated the antenna 360˚in azimuth to get an idea for how directional the antenna really is. There wasn’t much of a change in signal quality, so it isn’t very directional. If the transmitter were further away it may have been more dramatic. I am motivated to build a few more antennas, maybe with 1 and 2 directors to see which is better. With that said, I’m pretty satisfied, and I’m hoping for good weather this weekend.
b.t.w: Just to dispel any fears that the shield is shorted to the center conductor, as it appears in the above photo, it was, and I fixed it. Here is a photo of the feed point as it was when I tested it. Also, notice that I got my driven elements and directors confused when I wrote on the board 🙂
I find myself posting something someone else did again. I found this via Hack-a-Day, and it is an astonishingly well-done documentary about the culture that I value, and for which this blog is related. Enjoy.
Video of the iPhone TV Lift controller working!
This was probably one of my most time consuming projects. Hopefully I can do some justice to the time and work spent through this post. I should probably begin by describing the whole system. First, the TV is lifted up & down by a “Lift Tech” lift. By the way, they get the prize for the most original company name ever. Their controller box has a port that allows home automation systems to control its operation. They did a really good job of making it extensible. You can control it in a variety of ways: short one pair for going up, another for going down; short a pair for down, open for up; etc. I had intended to use the first mode, but I think I fried a channel on my opto-isolator. I ended up using the second method because it only required one channel. Unfortunately that means I can only have the TV up, or down. I wasn’t too disappointed, though, because I don’t expect to want it any other way very often 😉 .
The board I designed to interface the TV Lift to the server was fun to design and build, even though it was prone to error. I had originally intended to use the Microchip ENC28J60 ethernet controller. I thought it’d be cool to have the iPhone app connect directly to the board’s ethernet controller and microcontroller. Unfortunately, I screwed up the interface from the ethernet controller (specifically the physical layer circuitry) and the magnetics. This interface is harder than it looks, trust me. I thankfully included a serial port on the board (which I had other plans for) and used that instead. This choice made the microcontroller software extremely simple. All it really has to do is wait for a ‘d’ character over the serial port and lower the TV, a ‘u’ character lifts the TV, and a ‘s’ character queries the controller for the current state. I’ve included an image of the schematic for the board, in case you are curious about my lofty intentions.
If you’re interested, the board I used on my reflow soldering toaster oven page is the TV Lift board. Incase you don’t want to go over there, here is a picture of it mostly finished up:
There is one more thing that I had to change. For some reason the controller board that I made crashes after a while. I have to use a ladder to reboot it (power-cycle). Hauling the ladder around is annoying, and I don’t like doing it. To allow myself to reboot it remotely, I added a diode from the MCLR line (reboot) of the microcontroller to the RTS line of the serial port. The RTS line is used for modems from back in the day. Now I can use it to force MCLR low, to reboot the controller, if it’s “low” (-5 volts). It’s a hack, but what are you going to do?
The software for this project is deceptively simple. The iPhone software basically connects to the server using a socket, and if the “up” button is pressed it sends a ‘u’ over the socket, and a ‘d’ if the down button is pressed. That’s it! Server software is almost identical, however it listens to the return of the serial port and expects my controller board to return a ‘U’ or a ‘D’ from the ‘u’ and ‘d’ command. If these are not received, the board is reset and the command is tried again.
Well, that’s all there is. I hope you’ve enjoyed it, I know I have. Please, feel free to ask any questions in the comments section!
I used SecuritySpy by BTV to capture the frames. This software was intended for businesses interested in “Loss prevention,” otherwise known as catching shoplifters. For that reason, it’s a little spendy and the features aren’t perfect, but it does work rather well, and it’s reliable. There are 2 primary features I was looking for: Storing a time-lapse video, and providing web access to the camera. Security Spy does provide these functions, and it let me set a schedule for beginning and stopping the recording for each day on a weekly schedule. Also, you can modify the settings over the web interface. I had some trouble with SecuritySpy crashing, and by contacting support they provided me with an AppleScript that monitored the application and restarted it.
The problem with daily recordings, however, is that they need to be combined. About once a week, I would download the videos for that week and remove the times the crew wasn’t there, and combine them in iMovie. Now that the project is over I could never imagine the pain doing all that work in would sitting would cause.