Double-checking schematics. Found a 1.2 V power pin on chip was connected to the 1.5 V line. ⚡💥 🔥 #electronics
Found another bug. The chip is in SOT-23-5 but I used a VSSOP-8. It's a bit confusing when 10 variations of the same chip share a single datasheet... #electronics
Keep checking the schematics. Found another 3.3 V signal line was pulled up to 5 V... ⚡💥 🔥 #electronics
Just found a big DC-bias problem (who knows the Type-C mux has special DC-bias requirement on the USB SuperSpeed lines...) in the circuit before the board even arrives... Theoretically it should still work if I'm lucky enough, but unlikely. But I don't think ordering a new board right now is a good idea, perhaps I'll discover more bugs even on a nonfunctional board, better to wait and see. #electronics
Every circuit board automatically looks better when immersion gold is used, even if the layout sucks, like mine... #electronics
The idea of ordering a frameless stencil cut to the exact size of the board wasn't good at all, it's impossible to properly apply solder paste. One needs at least a few centimeters of margins for your hands/tapes/tools on... Have to reorder a standard stencil, $10 lesson learned... #electronics
QFN reflow soldering was a spectacular success, best joints I've ever seen. Unfortunately the first circuit board revision itself is doomed to failure due to multiple bugs in the design. #electronics
USB controller read the first byte from the blank EEPROM then immediately crashed. I actually thought it would read more bytes before it crashes... But not a bad sign, it means the controller is running. #electronics
EEPROM programmed. Now the USB controller seems to run firmware without problems, but the downstream USB load switch refuses to turn on. Looks like a GPIO / high-impedance / pull-up / pull-down problem, need to capture the power-on waveforms by soldering some jumpers to the board... What a pain, I really need to get some good SMD test clips and probe holders... #electronics
I knew most #electronics probe holders are outrageously expensive and there must be some "makeshift" versions that cost less. What I didn't expect is that all of those cheap ones are all marketed for hacking ECUs on cars. Apparently car modding is a big enough thing to give vendors an incentive to sell cheap probe holders for that. I guess they can be pretty useful for signals below 10 MHz.
Power-on waveforms captured. The /ENABLE signal is definitely floating, gives nothing but a smooth RC discharge, no doubts it doesn't work... #electronics
ProTip (ProbeTip?): See a TO-220 voltage regulator, a good spot to clip your test probe on, right? NEVER do this, especially, never clip on the tab or clip the probe from the back side. The plastic tip of your probe will be melted and destroyed after a while... #electronics
Soldered a pull-down resistor, the USB controller starts working. 🎉 But as expected, the USB 3 SuperSpeed line doesn't work due to a known bug. Time to do board v2. #electronics
The pinout of this chip is just evil, the two outputs are sandwiched between three inputs and it's impossible to bring them out without changing layers... #electronics
I've been thinking about it since yesterday: jumping a high-speed signal over an obstacle without vias is a common problem, so there MUST be somebody who makes an expensive & fancy component that solves exactly this problem, a high-tech jumper link for RF signals with impedance control. #TIL Yes it exists, it's called an "RF-RF crossover". #electronics
Another stupid mistake: selected an ancient 4016 analog switch as a bus multiplexer - the HCMOS version has 150 MHz bandwidth and available in SMD packages, old but not a problem right? Then started wondering why does my clock signal look like a sine wave... 74HC4016's on resistance is 100 Ω+, larger R in R x C = rise time degradation, Electricity 101 #electronics
Circuit board arrived tonight. Aligning the stencil and accurately placing the seven QFN chips with 0.4 mm pin pitch (two controllers, five ESD protectors) is the most stressful step, but now they all have been soldered onto the board, time to take a break before doing "Manual Optical Inspection" and soldering the rest of the board tomorrow. #electronics
Damn, I forgot to buy the 100K 0402 resistors, the circuit board is unusable for today. Just panic-ordered one roll from a local vendor, it should arrive by tomorrow, the shipping fee is 20x more expensive than the resistors... Always check your BOM right after you ordered the circuit board! Also, when ordering SMD resistors, double check to make sure you don't accidentally order the 4-in-1 resistor arrays (don't ask me how I know) ...#electronics
Another #electronics SNAFU - I added four "fiducials" to make it easier to align the stencil by hand and ordered the board with a stencil, but the CAM engineers at the factory silently deleted them! Normally they are correct - real fiducials are used by the computer for placing components onto the board, not for stencil printing, but it's not the case for me... Lesson learned: always select the "manual confirmation" option if you're doing anything unusual.
I think my circuit board can officially win the Fediverse stupid #electronics of the month award - the wires on my USB 3.0 connector footprint are ALL CROSSED, it should be 987654321, but I made it 123456789. The board is completely unusable.
VL670 development board design is now public. This is a ASIC that magically converts a USB 2.0 device to a USB 3.0 device, bypassing the signaling and bandwidth limitations of a USB 2.0 port. https://notabug.org/niconiconi/vl670
This is really strange. I found myself was working on exactly the same thing as whitequark  and marcan42 , all of us found the documentation and hardware around the same time. What a surreal situation. I may as well admit defeat, quit, and mail my chips to marcan42 instead... I guess it's time to setup a Twitter keyword alert and talk more openly about unfinished projects. #electronics
50 chips arrived in the package today, now started working on VL671. Looks highly compatible with VL670 and I can reuse the existing PCB without waiting for a new one for 10 days, neat. All I need is patching the LED signal. #electronics
Success! VL671 works flawlessly on the existing VL670 board. I think I need to mail this board to whitequark too. #electronics