DIY Knife Handle for Under $10

Panel Lift

Oil Change through Dip Stick Tube for MB C280 and Service Indicator Reset

Install Costco RO on existing faucet

Record in-flight audio with Samsung S8 phone

I am on my flight lessons, and one thing that's most challenging to me is to get the radio communication right. So I am thinking about recording the in-flight audio for me to review them afterward.

The simplest way is of course using my mobile phone. I have worked a bit on my headset before, so it is easy to pull audio from it. For my headset I bought a none working one off eBay and fixed it (replaced the battery and built a charger for it). So I paid a bit over $100 (and some sweat and my electronics know-how) for a nice noise cancellation headset that normally would run $400.

Back to the topic, it is easy to pull audio from it. To get that audio onto my mobile phone is not that trivial. I have a Samsung S8 which has a 3.5mm audio jack. I need to figure out which line the mic goes. Apparently there are two ways that the industry wire those jacks: OMTP and CTIA. These two web pages (Link1 and Link2) explained the difference.

But is my Samsung S8 an OMTP or CTIA? Both webpages seem to indicate that Samsung is in the OMTP camp. But this Reddit thread says with certainty that it is CTIA. So I am wiring it as CTIA.

It is also pretty obvious that the line level audio signal from the headphone is much stronger than what a mic would output. So I will definitely need to attenuate that. This can be done in a very simple way. Two resistors will make a working divider. An adjustable pot would be even better, but for now that will do.

However, when all is done, my recording app still does not record the audio from my headphone. Every recording seems to be from the on-phone mic. I tried various apps, some of them let me select the mic input source. But none of them has an option of external mic. What went wrong?

After some thinking, I think that the issue is that the phone did not recognize the external mic. I knew that some phone uses the impedance of the mic line to signal button pushes. I suspected the impedance, but most mic has impedance in the order of a hundred ohms or so. But after some Googling, it turns out that's exactly the issue. This xda-developers thread says that Samsung S8 detects external mic only when impedance is above 1K ohms. I tried it, and it turns out that I need about 2K ohms to have it recognized on my phone.

So a resistor is added to get the impedance in place, and everything works flawlessly there.

Start learning flying

I have finally decided to learn flying. Every kid has a dream of flying. I have wanted to do that for a very long time. But learning flying is not cheap. The airplane rental and instruction time are expensive, and there are a lot hours needed in order to be able to do that safely (you can't exactly slow down and pull off to the side of the road). But I have decided that I have to do it. Recently I sold my motorcycle, so I can get some money put aside for my flying lessons. Here we go!

Aeronca Champ from 1940s

For some strange reason, I am always fascinated by the taildraggers for a longest time. So when I started to learn flying recently, I took a path less taken. I wanted a place where I can have my lessons on a taildragger (instead of a Cessna 152). After some research, I found a school less than one hour from where I live, and now I am starting my lessons on a Champ (with no electricity). That's really cool! And my instructor is an wonderful gentleman who is in his late 80s (!!!) and he is as sharp as ever. Talking about classic old school!

How cool it is that I am flying on an airplane built 30 years after Wright brothers invented, with no electricity on board! You can just slide open the window and stick your hands out to feel the wind. That's exactly the same way our pioneers are doing flying!

Fixing a gunked up motorcycle carburetor

I haven't ridden my motorcycle for a long while (almost a year). So when I got it up last week, it would not run. So it is time to do some fixup work.

The Problem: The battery has been connected to a charger all the time, so it turns. The motor starts with choke on, so that was a good sign. I knew the carburetor has to be gunked up, and my plan is as long as it starts I will ride it for a while with some cleaner added in the fuel to clean it up. So it is a welcomed sign that the engine starts with choke. The troubles comes when I tried to give it some throttle. Just a little turn on the throttle stalls the motor. I did manage to get through the stall point and really reved up the engine but the second I let go the throttle, the engine went off.

The Hypothesis: After some Googling and thinking, I figured out that this is a problem with the pilot of the carburetor. The engine runs under chokes, so most of the system is doing fine. It does rev up at full throttle, so the main jet is not stuck. So it is the pilot that is clogged. The telltale sign is that the engine stalls when throttle is applied. At low throttle, the fuel is mostly supplied by the pilot system, so it must be those that are clogged.


The Fixups: It is relatively simple to take out the carburetor on a motorcycle. Here is a picture of the under side of the carburetor with the fuel bowl removed. The arrow shows the flow of air / fuel and mixture inside the carburetor body. On the pilot system, the air comes in on a long passage, picks up fuel at pilot jet, and goes into venturi at the pilot drill points and the air screw.

I took out the needle jet and the pilot jet. The needle jet is relative easy to take out, and it is not clogged (because it relatively big in size).

The pilot jet is a struggle to take out, because it is pretty deep inside the hole, and is glued to the body by the gunk. Some penetration oil did manage to loosen it up enough to take out. The pilot jet is indeed all clogged.

The holes in the pilot jet is very small. It read that people (the professionals) advice against enlarging or cleaning these holes, but with an old motorcycle like mine, I got to do whatever I felt making sense. I am not sure if I can find those replacement parts.

The head of the pilot jet has number "35" stamped on it. I guess it probably means that the hole is 35/100 of a millimeter in diameter.  (By the way, the K mark at the top indicates that this is a Kaihin part, according to this page I found.) I happened to have a lot of tiny drill bits (in various sizes) from previous work. I took those out and soon found one that seems to go through the hole just right. One of the pilot jet has a hole so clogged, that I have to put the drill bit on my Dremel tool to drill through it.

Now it is time to clean things up and put it all together. And the engine starts right away, and goes well when opening the throttle. I guess now I will need to take it out a bit more frequently.