Sunday, May 20, 2018

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.

Thursday, August 3, 2017

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!

Saturday, April 15, 2017

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.


Saturday, January 9, 2016

Craftsman 109 Lathe - Chuck Backplate and Fitting

I have made a new spindle for my Craftsman 109 lathe. And I found that all the chucks need to be refitted. I have two chucks: a 4-jaw with 3/4-16 thread, and a 3-jaw with 1/2-20 thread.

When I mounted the 4-jaw and indicated it, I found that it is off now with the new spindle. I have tried to turn the surface of the front and back of the 3/4 adapter, but it does not help. I think it is because that the center line of the inside and outside thread are not matching with the new spindle. Since the 4 jaws are adjusted independently, there is not much need to remake the adapter. The only downside is there might be a bit off center mass, but that may not be much of a problem for the limited precision of my lathe.

The 3-jaw is a different story. It is off by quite a bit. My 3-jaw has a plain back and has a cast iron backplate adapter. But when I took them apart and attempt to refit it, I found that it may have never been properly fitted previously. The spigot is cut a bit too small. I will have to turn it all flat and turn a new one from what is left. I happen to have a 1" thick piece of 3" rod aluminum. So I decide that I will use that to make a new backplate and leave the old one alone.

I did some research on whether aluminum is strong enough as the backplate (the standard material is cast iron), and found no definite conclusion. Then I decided that I will just go ahead and do it. The thread mating between the backplate and spindle might be a bit soft, but it should work if I use it carefully.

So I mounted my 4-jaw chuck with the jaw facing outside (which holds the 3" piece with no problem) and started working on the backplate. The procedure is pretty simple, and there are plenty of information on Internet on how to do it. So I will skip the details here. Soon, I have this blank piece of backplate.

The hard part of this project is to locate the mounting holes. The location of the mounting holes is not super critical as the precision of the fit is decided by the size of the spigot. But I like to make them as accurate as possible. Instead of measuring the hole circle radius and dividing the circle to three parts, I decided to go with a simple method of making a few transfer punches as indicated in the picture. The mounting holes are M6-1.0. So I turned a few M6 screws down to having a small spike in the middle and cut a off-center slot so I can use screw drivers to get them in and out of the mounting holes on the chuck. A few light taps marks the location on the backplate and they are drilled to through holes for the M6 mounting bolts to pass through. The holes are numbered and marked as well as the mounting holes on the chuck, so they are always going back the same way.

With some very careful turning, I have my backplate fitted for the 3-jaw chuck. The TIR on the backplate is almost nothing, but to my surprise the TIR on the perimeter of the chuck is 5 thou. I re-check the TIR of the spigot and found it to be nearly zero. So the chuck is not perfectly centered with the register. With a test piece mounted (and tightened with the best chuck wrench hole), the TIR is about 2 thou. That is much better than before. I will probably need to grind the inside of the jaws someday, but for now, that will do.

Here is my 3-jaw chuck mounted with the newly fitted backplate. Another good thing about my backplate is that it is about 1/2 inch thinner than the old backplate, which moved the chuck a bit closer to the spindle bearing (but still not close enough as the 4-jaw).


Wednesday, December 9, 2015

Craftsman 109 Lathe - New Homemade Spindle

I  have known that the spindle on my lathe is old and worn out. I am not sure if it is bent, but I like to replace it. There are spindles available on eBay and Home Shop Supply. They run for about $100. But where the fun is if I just bought it.

There are people who has made the spindles themselves. For example, this gentleman in SHDesigns made one from tool steel, and has a page for it. But he turned it on an Atlas/Craftsman 12x36. I don't have a machine of that size or accuracy. All I have is a semi-working Craftsman 109. And even if it cuts, I am not sure if I can make the finishing smooth enough for the bearing surface.

I have been thinking and search for a while. And one day, I realized something. We all know that the spindle size of the Craftsman 109 is 0.551". That is a strange number. I have seen people doing things in strange numbers, but there has to be a reason. And it turns out that 0.551" is 14mm. The all American Craftsman has a metric heart. How interesting is that.

So all I got to do is to find a grounded 14mm rod, and that could be my new spindle. But what about the collar part? I have spent quite some time thinking about it, and there are a few ways I came up with. I did a few experiment to decide the precision of my cut and measurement, and decided that I can bore the hole precise enough for an interference fit (or shrink fit), with my BBQ stove as heating source (no need for a propane torch).



So here we go. First I got the 14mm rod from eBay. It is grounded 1144 steel. Even though it is not as hard as tool steel, I figured that it will do for me now. The piece I got is 24 inches long, just enough to make three spindles (the original spindle is about 7-1/2" long).

So I cut a piece of 12L14 that is about 3/4 inch long, and bored a hole that is just one thou smaller than the spindle rod (which measured to be 0.550"). For some reason, I can not even bore a smooth surface in the collar. But I figured that this would be a good thing here, as it would grab tighter when the two surfaces are shrink fit together.

Before I shrink fit, I made a wood jig (that is nothing more than a large enough hole drilled for about 1 inch deep). That's how much I like the spindle to stick out. And then I put that collar piece on the BBQ stove. After a while, I took it out, put on the wood jig, and stick in the spindle piece. I even brought a hammer, in case I will have to force it in. But it slides right through with a light tap. I kind of worried if I have machined them too close, but it turned out beautifully when everything is cooled down.

Next I put it on my lathe to finish the backside of the collar. The rest of it can be machined when the spindle is on the lathe.

The next challenge is to get the groove for the Woodruff key. For this I just used my Dremal tool with a disk shaped cutter. It is a bit larger than the original, but it works its way in just fine.

Here are the new spindle and the old spindle show side-by-side. As one can see, I left a bit more material on the new spindle, as those will be cut down in the future when fitting the chucks. Plus I like to have some safety margin to give my shrink fit more surface to grab on.

The old spindle is shown here. As one can see, it has been worn out quite a bit on its bearing surface. I guess that this spindle might have never been replaced since the lathe is first sold in late 1940s. It is an old lathe.

Now the spindle is put on the lathe in its place, and nose of the spindle is cut down to 0.5 inches, ready to be threaded. The spindle nose on the 109 lathe has a 1/2-20 thread. It is great that I have fitted my lathe with all the necessary threading gears so I can cut those threads in place.

Because these threads are so close to the end of the ways, we need to be very careful in setting it up. I happened to have grounded a v-shaped cutter that is tilted to the right. So as we can see here, I can cut pretty close to the register surface and still have room for the indicator wheels.


Cutting the threads are largely uneventful. I did have a few mistakes when the gear pops out. But I got it realigned easily. I finished the thread with a die. As always, that is not an easy work, and took significant force at the end. The die set I have is a cheapo set from Harbor Freight. Maybe I will need a better die set someday.

So finally, here is my new spindle on the lathe. All home made cheaply and proudly on the Craftsman 109 lathe I have.