Archive for March, 2010
Well, as a (perhaps welcome ;)) deviation from the spectrum analyzer posts, I’ve spent a little time working on repairing a security camera I’ve been hanging onto for a while. I’ve been toying with the idea of installing it near the radio control flying field as someone in the club knows the owner of a nearby business.
The problem with the camera is that it has trouble switching from nighttime mode to daytime mode. At night, it is sensitive to Near Infrared light (such as what is transmitter from your remote control). During the day, however, this sensitivity makes the colors look strange. To cope with this, they have a filter that slides in front of the lens for the daytime. This filter binds, and because of this, the camera is always in nighttime mode. I decided to go ahead and disassemble the camera to try to fix it. My motto: If it’s broke and out of warranty, take it apart! 🙂
You can (kinda) see in this photo the image sensor. This metal mount can move forward and back to accommodate different lenses and adjust their focal length.
Removing the bottom cover reveals the power conversion board.
Removing the top cover reveals the PCMCIA slot. This camera is kinda cool in that it can accommodate either a memory card or a wireless LAN card in this slot. Also, there is an ethernet port on the back. It has an embedded web interface that allows the control of camera functions and viewing live video. Apparently, there is the ability to get some information from the serial port, but I haven’t found any information about it.
Like I mentioned before, the front lens mount can be adjusted front-to-back. The black screw near the top of the frame is used to secure the mount. More to the right of the frame, the spring is used to press the mount against a set of wedges that control the depth setting. The 4-pin connector goes to the lens iris, which is kinda like the aperture of a still camera.
This is the front of the camera disassembled. The image sensor is still attached to the camera frame. The black piece of plastic is the filter module, and the other piece is the metal frame for mounting the lens and adjusting the focal length.
This is the device causing all the trouble. The slight green tint in the left frame is the IR block filter, and the right is clear. The motor is a small gear-head motor attached to a worm gear. The worm gear has very shallow cuts in it. The spring pushes down on a small plastic follower. The whole system is intended to allow the worm gear to continue turning even if the system is jammed. I think this is so that limit switches aren’t necessary. I figured that the problems I’m having are due to excessive friction, which would cause the frame to remain static while the worm gear turns. My first thought was to place a little petroleum jelly on the sliding surfaces. I re-assembled the front of the camera and found that the problem remained. However, I noticed that when the lens mount was all the way against the camera it would stick. I could then solve the problem by keeping the lens not-quite against the camera.
Before re-assembling the camera, I decided to lubricate the adjustment assembly. The black plastic ring on the right includes the adjustment wedges. The middle ring is the precision-machined lens mount with a channel for the plastic ring. The punched metal piece on the left completes the assembly.
Anyway, I put the camera back together. It works great now. I’m a little embarrassed to admit that the problem was simply that the lens can’t be in the closest setting for the filters to work. At least everything went back together without a hitch. 🙂
I’ve decided to hold off posting spectrum analyzer modules until they’re complete. I’ve been collecting tons of pictures along the way, so hopefully the post for each module will be interesting and visually appealing. With that in mind, I can’t post about any of the modules with the exception of this one.
For whatever reason, my kit didn’t come with any voltage regulators, and this is the only module besides the mixers from my last post that don’t use any. The IF Amplifier, as the name implies, amplifies the Intermediate Frequency on the analyzer. I made a simplified version of the block diagram from Scotty’s site. I’ve also indicated the modules I’ve finished in green.
As you can probably see, there’s a lot to be done. Luckily both DDSs, the Log Detector, ADC, Control Board, and one PLO are done once I get some parts to replace the missing ones. I also need some parts for the Master Oscillator. Once that (actually quite small) order comes in, I’ll be almost finished with the boards.
Anyway, back to the amplifier. I was one of the first people on an order of boards back in August ’08 because I agreed to look-over a new revision of the design files. Of course, by having me look them over essentially guaranteed that there would be errors. As it happens there was an error on this board. The engineering change order (ECO) is luckily quite simple, the only problem was that a short section of the border was missing. Here is a photo of the completed fix:
You should be able to see that along the border there is some solder wick saturated with solder bridging the gap, and connecting to the capacitor. Also, on (at least) the 2 resistors (R3 and R4) there are tiny balls of solder. These happen during the reflow stage when a bit of solder squeezes out from underneath the device. I haven’t gone over the board picking all these out yet in this photo. I think it’s important to remove all of these because they may cause shorts. Also, you may be able to see a slight, shiny, residue around everything. This is the solder flux that’s included in the solder paste. I remove this later with some 99% rubbing alcohol.
This is the completed amplifier board. There are actually 2 amplifiers here, mirrored. In practice, the output of one will be the input of the other. This serves to roughly double the gain. Finally, notice on the right side, that many of the parts have been omitted. On the schematic, Scotty simplified this section. Technically, he has 2 zero-ohm resistors (basically jumpers) in addition to the capacitor. I chose to just jump the capacitor across and leave the resistors out.
Anyway, I enjoyed building this one. I hope you’ve enjoyed reading about it. I can’t wait to finish the other ones!
I’ve verified each of the 3 mixers that I need for the spectrum analyzer. The one above is mixer 2. The schematic for this mixer is available from Scotty’s site.
I’ve also verified mixer 1 against the schematic. There have been 2 optional revisions posted that aren’t included on mine. I’m going to add them later, but only if necessary.
Finally, mixer three is complete, and verified against the schematic. This one isn’t strictly needed for the spectrum analyzer, however it is necessary for the tracking generator. A tracking generator is a module that generates a signal that matches what the analyzer is tuned to. This is useful for tuning filters, or other passive devices.
I’m missing some parts that I need to complete the control board. I hope to get replacements soon, so I can begin testing some of these modules… Stay tuned!
IMPORTANT!! — I’ve made a special page for my construction and testing of the spectrum analyzer. It’s available on the navigation bar below the blog title banner, or here.
A while back I bought a spectrum analyzer kit. It can display waveforms in the frequency domain from 0 to 1000 Mhz. I haven’t worked on it for a while, but I’ve decided to start working on it again. If you’re interested in more information, there is a webpage for the analyzer by the guy who designed it, and there’s a Yahoo group, also. If you’re really-really interested there is a group buy open (until the 28th of march 2010) here. Anyway, I’m sure it’s of limited use to my usual readers (thanks, friends & family! [oh who am I kidding, most of my family doesn’t read this 😉 ]), but it may be useful to others working on the kit. I’ll post the “annotated” CAD images for each board here, and add images of the completed boards when I finish them. Who knows, it may be interesting for someone. Also, I’ll include my thoughts and observations while building these boards. Finally, not all the boards that come with the kit include annotated layouts, so I’ll have to dig around and figure out what they do and what to put on them 😉 Read the rest of this entry »