Fixing a misfire during acceleration in a 1992 Honda Civic

I took some packages to the post office today, and was surprised to find my 1992 Honda Civic was having a very bad day. It was misfiring during acceleration at low-mid RPM. Idle was smooth and cruising was fine, but any normal amount of acceleration from a stoplight or stop sign produced an extremely loping, uneven amount of power. The car was drivable, but just barely.

I took out a couple spark plugs, and was surprised to find the gap had become huge -- around .075"! The plugs appeared to be worn out. I figured this had to be problem. I got some new NGK plugs, and unfortunately the problem persisted. I checked the compression in each cylinder, and they were all 150 psi +/- 5 psi. After a short consultation with my dad, I decided to replace all of the common ignition parts with real Honda replacements: distributor cap, rotor, and plug wires. This did the trick! The car was back to normal, and running strong. The original cap and rotor were Honda parts, but the plug wires appeared to be aftermarket (Prestolite). Dad and I agreed that aftermarket plug wires should be avoided altogether. Just bite the bullet, and buy OEM wires. They'll last much longer.

Even though it is difficult to see in this photo, the old plug (right) has a gap almost twice that of the new plug (left). This too-large gap in all four plugs might have contributed to the destruction of the plug wires.

Finishing the refrigerator conversion project

In my last post, I had just finished charging the "new" refrigerator with R134a. I was surprised that it worked at all, and it was still working the next day, so something must be correct. I used some expanding foam to fill up the large square hole left by the thermoelectric module in the bottom of the fridge. The clear vinyl tube is a hose that I connected to a drain on the inside of the fridge. If (when) the evaporator defrosts, I am sure there will be a fair bit of condensate dripped out. I put a small stainless tray on top of the compressor to catch the water.

I also used the fridge's existing thermostat (the white tube on the right). The manufacturer setup the thermostat so that it would regulate the temperature on the evaporator itself. The thermostat has a capillary tube that is clipped onto the evaporator and a large knob with numbers 1 to 7 (like any refrigerator). I also filled up the hole through which the refrigerant lines and thermostat enter the fridge with expanding foam.



While the existing thermostat works well, the table has a nice cutout for a two-digit 7-segment display and four buttons. The thermoelectric fridge came with a digital thermostat, and I made the cutout in the tabletop specifically for it. I would like to keep the digital thermostat feature, so I am building one with an Arduino microprocessor.

Here is the rear of the completed table with white thermostat control knob at lower left. I've already written some Arduino code for the digital thermostat, and will probably be implementing that soon. In the meantime, my table refrigerator is now frosty cold, and using less power than the thermoelectric model.

Retrofitting a thermoelectric refrigerator with a conventional compressor system

A couple years ago, I built a nice wooden table that housed a small refrigerator. The idea is that it keeps drinks handy in the living room for parties and guests. It's also cool, and fits with my idea of what "functional furniture" should be.

I chose a refrigerator meant for storing wine because it had a nice glass door, was pretty small, was very quiet, and could operate facing upwards because the thermoelectric device doesn't care about its orientation. I knew that thermoelectric refrigerators generally suck at actually refrigerating, and this one was not exception.
On really hot days, the fridge would get up to 5o-60*F, which is cool, but not nearly as nice as drinking 40*F beverages. The other problem is that it draws 70W, essentially constantly. This comes out to 613 KWh/year. Most small conventional refrigerators use around 300 KWh/year. Also, I like to tinker and wanted to mess around with a refrigerant system.



I bought a small 1.8 cu ft Haier fridge off craigslist for $15. Geez, can't beat that! My first task was to pull out all of the system components from the insulated box. This required draining the system of refrigerant through a small hole that I drilled in the compressor fill tube. Before doing this, I checked the label, and it indicated the system used 1.6oz of R134a. I can buy R134a at the auto parts store, so I will be able to refill the system.


I de-soldered the tiny capillary line from the accumulator / dryer and de-soldered the suction line on the compressor. I used an oxy-acetylene torch to heat the joint, then I just pulled the tubes apart when the solder became molten.

Here is the evaporator liberated from the fridge.



Luckily, with one flap unfolded, the evaporator fit perfectly in the thermoelectric cooler (TEC) fridge.


I mounted the compressor underneath the table (also getting very lucky that there was enough clearance). I cleaned the copper tubes carefully, then re-soldered them with silver solder and some paste flux. I had to extend the suction tube by a few inches, and so I just got some tube that fit around the existing line and soldered it to the outside.


I soldered the capillary tube back into the dryer, and put a valve on the compressor fill tube. The system was sealed at this point. Now, I connected my vacuum pump (Welch 1400) with a micron vacuum gauge and a tee that connected to a can of R134a. I positioned the can on a sensitive scale so that I could meter out 1.6 oz of refrigerant.

I pulled a 375 micron vacuum in about 15 minutes or so. I even ran the compressor while the system was under vacuum. It raised the pressure just a couple hundred microns, then it settled back down quickly, so I felt the system was dry and sealed.


After I metered out 1.6oz, which only took a few seconds with the valve just cracked open, I tightly closed the valve that I added to the fill tube, and was very pleased to see feel the evaporator getting very cold.

Tomorrow, I will re-insulate the TEC fridge and hopefully give it a final test.

Experimenting with a "liquid lens"

A couple months ago, I started to investigate building an auto-focus mechanism for cameras that could operate in high magnetic fields. This was for a work project (where I build MRI-compatible devices). Inside an MRI machine, the base magnetic field is usually 1.5 or 3 Tesla. At these fields, any motor or solenoid that relies on manipulating a local magnetic field will not work. Unfortunately, manipulating magnetic fields is one of the easiest ways to convert electricity into physical movement, so most auto-focus assemblies are built this way. There are some
alternatives, though:

Piezo "ultrasonic" ring motors. Many high-end DSLR (and SLR) lenses have silent ring motors that vibrate at ultrasonic frequencies to create rotation. Great! The only problem is that they are built from steel, and the steel cannot be used in the MRI environment. They are also too big -- I need a tiny lens about 1/4" in diameter, not 2" like a DSLR lens

Piezo wiggler motors. Looks interesting, but getting a sample is near impossible. The screw assembly is probably steel, and the system requires a fairly rigid and complex slide system

Liquid lenses. These lenses are built by sealing a small amount of water and oil inside a shirt button-shaped capsule. The walls of the capsule are metal with glass windows on the faces of the button. The water and oil will not mix, and the boundary between the fluids will bend light because the two liquids have different refractive indices. If the walls of the capsule are charged with electrical current, the shape of the water droplet will change because of electrostatic attraction. (check this out: http://www.youtube.com/watch?v=p1f6zLysilU ) The oil is made up of non-polar molecules, so it does not share this same attraction. By controlling the voltage on the capsule walls, the shape of the water can be controlled and thus the focal length of the lens formed by the water-oil interface. Neat!


The liquid lens is the metallic button-shaped thing on the left. I built a holder for the lens out of 1" squares of copper clad board.

There are only one or two manufacturers of liquid lenses: Varioptic, Philips, and maybe Siemens. Philips and Siemens would not discuss the liquid lens and would not sell any samples. Varioptic would send samples -- only $340 for each lens! What?! The evaluation kit was a mere $4000, while the full developer's kit was $12,750. I kid you not. What kind of company would charge a potential customer $12k for the privilege of testing their products? Insane!

Anyway, since I couldn't deal with any of the manufacturers directly, I set about finding an off-the-shelf product that contained a liquid lens. After many hours of searching, I found an actual product that had the Varioptic lens in it: Digitus DA-70817. There were many other prototypes and press releases for other liquid lens products, but it seems the Digitus camera is the only mass-produced device right now. Unfortunately, it is not available in the USA. It's not on eBay. Amazon.de has it, but will not ship to the USA. After many more hours of searching, I got in touch with a German distribution company called Assmann (no joke). I exchanged a few emails with a friendly person there, and she sent me five of these cameras (about 25 euro apiece with the usual outrageous international shipping charge).

I removed the lens from one of the cameras and mounted it between two pieces of copper clad board. To make the lens change focal length, I need to supply 0-70V AC to the lens. AC is required to prevent the liquid in the lens from polarizing over time and losing effectiveness. The voltage needs to be fairly high to deform the water drop sufficiently, and also needs to be changed rapidly for quick changes in focal length. Fortunately, there are two companies that make ICs specifically designed to directly drive liquid lenses. Unfortunately, one of the companies, Maxim, will not sell samples of their chip, and they will not even give out datasheets for it. Take a look: http://www.maxim-ic.com/req_full_ds.cfm?action=request&id=5949 How rude is that? WTF?! The other company that makes liquid lens drivers is Supertex. They will sell samples of their HV892 at a reasonable price, but the chip is only made in a 10-lead 4mm x 4mm DFN package with .65mm pitch. Apparently, this SMD footprint is so unusual, there are no DIP converters available from anywhere. Geeeez! I ended up designing my own PCB for the chip and having them made at http://www.expresspcb.com/. Here it is:

I interfaced the chip to an Arduino Duemilanove. The Arduino sends a value between 1 and 255 to the HV892 via the I2C bus. The value controls the HV892 output voltage, and hence the lens's focal length. I am not sure what the mathematical relationship is





I used a laser pointer to show the different focal lengths that the lens can achieve.

Sharpening planer / jointer knives

In short, sharpening planer and jointer blades is more difficult than it looks, and is probably not worth it. Get them sharpened or buy replacements if you value your time. I originally was inspired by this article:
http://www.ablett.jp/workshop/oak/doug_abbott.htm

I built a similar jig that looked like this:

I had used the sandpaper-on-glass technique for other projects, so I felt it could work well for sharpening knives. It works, but it's SLOW. My knives were in admittedly bad shape (very bad shape -- see picture) and needed a lot of material removed. I resorted to using a power sander to take off the initial material. Also my jig is not as good as the one shown in the link because tightening the screws will make the jig not be perfectly straight anymore.


Before and after

Yeah, it's sharp! The blades appear to be bi-metallic. I am not sure if all planer blades are like this, but there are definitely two different types of steels joined together.