Dusty pics

Pretty good for a messy link like that. The flat spot halfway up might be a problem with longer links.

Or maybe you’re measuring the near end and it’s fine at the far end.

We use a lot of U.FL connectors for that sort of thing.

Cheers

Phil Hobbs

That's the far end, on the baby board at the ribbon cable connector. If we need it, we put a TinyLogic receiver/buffer right there. Source terminated by the FPGA i/o cell.

The ribbon cable pinout alternates a number of fast signals with equivalent grounds. That seems to be about 75 ohms by TDR, so the PCB traces are 75 too. Looks pretty good, but a harder FPGA drive strength might crisp it up a bit. Gotta try that.

Hey, I just received the AoE X-chapters rev 2 book. I think I ordered it about 6 months ago.

We hate U.FL connectors!

Mine got here yesterday. Looks good so far, though I’m way too flattened with lawyering to sit down with it yet.

I know. Weird.

A little flick of the wrist and they go on or off, zilch capacitance, 6 GHz, size of a SOT23, all for 30 cents or so. We sprinkle them all over the place for debug, then leave them mostly unpopulated.

Good Medicine, as long as you don’t have to make the cables!

Cheers

Phil Hobbs

What's the big yellow flat thing?

Capacitor? VDR?

PTC self-resetting fuse. The user might, for instance, apply power backwards and we want the box to survive.

We've tried the surface-mount versions before and they are not reliable.

I had a battle with production about that part. They wanted to kink the leads, which lifted the ptc up and made it hit the top cover.

I won.

The cool thing about that design is that both boards work perfectly on rev A, first try, with zero changes. Both have parts on both sides.

One of my guys wants to change one resistor value, to shift some dissipation and reduce the temperature rise of a linear regulator.

The RP2040 uP and the Efinix FPGA are both awesome parts.

John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics

OK I see. Reverse diode to ground after it?

Too much drop in a series diode? Power MOSFET as serial protection switch?

Yes, I may try that in a next project that uses a FPGA.

There are salt and pepper removal filters in most image processing tools to help with this. Might also be worth using a polarising filter so you don't see so much reflection of the room (or do it in a darkened room).

My preference is to take images of screens skewed slightly off axis with a black card reflected in the screen. Then fix it up to square in post processing. That way you get a very clean image.

A TVS. If one of our esteemed customers applies -24 or +60 the TVS will clamp and maybe fail. A fried/shorted TVS will sacrifice itself to save the rest of the board, and allow us to assign blame.

A series diode would be OK. I don't trust semiconductors for primary power protection. I tested a TI e-fuse and it was awful.

We embedd the FPGA config into the Pi executable file, so there is a single USB file drag-and-drop to field upgrade all the code.

At powerup time, we use an SPI block to configure the FPGA and then use the same SPI to read/write FPGA registers.

I can share our uP/FPGA schematic pages. It wasn't entirely obvious how to do all that. The Efinix data sheet is like a murder mystery with clues here and there.

We did a proto board to test that and to test some other circuits and parts.

John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics

Yeah, there must be an AI thing to remove dust.

A paint brush worked in this case.

It's hard to take a good pic of a PC board. That's another issue.

John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics

I will have to hand solder that.. with wires and adaptors ;-)

Don't those scopes have a 'dump screen as image' option?

Anyways I just take a picture with my Canon camera

No it is not really that hard:

HP did that in some of their linear regulator power supplies. A zener diode of voltage just above the regulated voltage, which would fail, go short circuit, and blow a fuse. use to think that a bit crude, but did work. Seen several eamples of that.

On some models, with 115/230 volt line rating, uk line at 245 could overheat the series regulator transistor, go short, and enable the zener diode to do it's work.

Yes, and a thyristor with a zener to the gate had a bit more shorting power for too high voltages.

One of my interns introduced us to JLCPCB. Now making PCBs as protos is cheap and easy.

It's hard to find adapters for a lot of parts. When we do proto PCBs, we toss in adapters or goofy circuits too.

Yea, but I am not doing things for production, just to experiment and learn out of curiosity. If it works I usually open-source stuff, then the world takes over Year 2017: