Holiday Trinket: Third Time's a Charm?

Nope.

I got some new solder paste to see if it was the source of the issue:

Fresh paste.

Used the stencil to apply the paste to a new PCB:

Paste applied.

 Placed all the components:

Ready for heating.

Fired up the skillet:

All soldered in place. (I had to manually solder the
center LED as it didn't reflow properly).

And after soldering the battery holder and switch to the back side, I was greeted by this:

More than before! And alternating!

A non-oscillating circuit. I tried to apply different voltages as the supply (since during simulation I realized low voltages could cause the circuit to lock up) and none of them worked. I'll see what else I can do to attempt to debug this later.

Holiday Trinket: Take Two

Turns out it was essentially impossible to solder the transistors upside down; It didn't help that my solder paste was "expired" and incredibly runny. The method of using a toothpick like CNLohr failed miserably on the tiny pads. Despite knowing that everything was going to go badly, I still tried to put one trinket together.

I ordered a new set of PCBs with the transistors corrected and got them a few weeks later. Today I attempted to assemble a trinket again, but this time with the aid of a stencil. I ordered a simple plastic solder stencil from OSHStencils so I wouldn't need to precisely dab solder paste anymore.

Stencil in hand.

Using the same runny solder paste from before, I just had to spread a blob of paste over the stencil using the provided plastic card until all the holes were filled.

Stencil aligned and ready to go.

Holiday Trinkets

I've been messing around with ring oscillators and decided to make a little holiday-themed trinket to give out. It was a good opportunity to get back into PCB layout and to learn how to use LTSPICE to simulate the circuit.

I originally wanted white LEDs, but with their high voltage drop and the 3V of the coin cell, they would never light up. In the end I had to use red LEDs with their Vf of ~1.8V. (This is when a green soldermask is more fitting for the occasion and better complements the red. However, the purple still looks amazing.)

Snowflakes!

Backside!

Of course, since I didn't think there could be an error in layout after checking that the schematic was right, there was an error. An error I found a few days after sending off the design.

Turns out the pin out for the default 2N3904 in KiCAD differs from the SMD MMBT3904 (which I really should have checked the datasheet for). The base and collector pins have swapped pin numbers, so when I solder up these circuits, I will have to flip the transistors upside down. And I thought I would have learned from the nixie tube clock. Oh well.

Ray Tracing and College

Working on a ray tracer has been quite fun, especially when debugging it when the image doesn't come out right.

I don't think that box is supposed to be cut off.
This was a bug with transforming the bounding box with a rotation.

It's mainly based off of Peter Shirley's raytracer in the Ray Tracing in One Weekend series of books, just implemented in Java. It's certainly not fast, but that's not really a big issue since I'm treating this renderer mostly as toy to learn more about the fundamentals of ray tracing.

Teapot! This uses a rather inaccurate model of glossy surfaces
but looks nice.

Reverse Polarity

A quick update during AP testing. I was messing around with a gear motor I got a while back (and used before for the barn door tracker)...

...and destroyed the encoder. In preparation for another project, I was working on creating a controller to regulate the speed of the motor and how much the shaft rotates. (Closed-loop speed and position control)

Dead.

Despite remembering each other time I used the encoder to check the pin out on the datasheet, I decided it was fairly safe to assume that the red wire was for VCC, the two wires in the middle for the encoder outputs, and the last wire for GND.

Big mistake. Turns out the red wire was GND and what I thought was GND was VCC. Add that to no reverse polarity protection, and you get a dead encoder. Bad on my part for not checking the datasheet again, but why is the GND wire colored red!

At least I got the motor/encoder combo used for only $20, and I can still use the nice Globe motor and gearbox. I looked up how much the encoder was worth new, and it was ~$50! Those 500 PPR and signal filtering don't come cheap. Oh well.

BatteryBoard: Osu! Keyboard

Today I made a quick project: a Osu! keyboard for a friend. I used an Arduino Pro Micro and Red Cherry MX switches.

Volume Control

After a quick test with the new IEMs, I decided to glue the shells together permanently with epoxy. The final result is rather nice looking:

Ooh.