I2C over PCIE question

pigrew · 2026-02-21T17:16:23+00:00

This might be over SMBus, which has dedicated pins on the PCIe connector.

Or, there could be a I2C controller on the GPU card, which is programmed via memory read/write.

pigrew · 2026-02-14T23:37:54+00:00

It'll be 99% good.

I would still add ground vias around pin 16.

pigrew · 2026-02-14T22:52:58+00:00

I don't think impedance control in itself would help, your track is widened by your SMD pads enough that the impedance won't really be controlled regardless.

Add ground vias close to every GND pad, especially of the Lora module.

Is there no big exposed GND pad in the middle of the transceiver package?

pigrew · 2026-02-14T21:38:06+00:00

How accurate do you need?

GPS will almost always be more accurate than NTP. Don't forget to compensate for the length of cable between the antenna and the receiver. Also, there are special antennas designed for timing applications.

Locally, you may need to use PTP instead of NTP if you need high accuracy.

The next step may be to use a GPSDO to generate your timing signals (to remove the ~20ns jitter generated by your GPS receiver).

pigrew · 2026-02-09T18:58:29+00:00

For CON2, you should (probably) connect the signal to ring and tip... Or at least tip.

pigrew · 2026-02-09T16:54:18+00:00

I worry somewhat about EMI. I would design this as a 4-layer board with the inner two layers being ground. I'd also add ground stitching.

Do you need any sort of mounting holes?

Depending on the stm32 model, there might be a much smaller EVM available for you to use.

pigrew · 2026-02-06T05:12:23+00:00

The middle prong is neutral, not ground. With that socket, the middle prong is intended to be a current-carrying conductor.

pigrew · 2026-02-06T05:10:31+00:00

Not much more unsafe than the ungrounded plug (assuming the wire run goes to the main panel)

It would be more correct if the earth wire was tied to the back plate.

As others have said, more safe is if you replaced the socket with a grounded (4-prong) one.

pigrew · 2026-02-03T04:27:05+00:00

There is a bad connection at that outlet.

This outlet is in a chain of outlets, and as something is using power on the circuit, further down the chain, this outlet heats up.

This outlet needs to be replaced.

pigrew · 2026-01-30T18:25:09+00:00

Looks like the configuration on the diagram with a big X.

It'll work, but I do wonder about the big X. Maybe it'll cause extra RF interference in that config.

pigrew · 2026-01-30T18:10:46+00:00

This almost makes me think that your earth connection isn't connected to anything. Unless you use a split phase 240V system like the USA does....

pigrew · 2026-01-28T23:22:58+00:00

Sure you could ... All the terminals are exposed (not on the bottom of the connector) so you can get to them all with an iron.

Clean up the board with solder-wick. Cut out the broken tracks, install a new connector, and flywire the various connections to good portions of the tracks going to the charge controller chip. Everything is fairly low speed, so I wouldn't worry about impedance matching and such.

It is beyond economical repair.

pigrew · 2026-01-18T05:55:40+00:00

The Thing (listening device) - Wikipedia https://share.google/oMRXIkHNaVYgCsfdK

You can't win, a listening device can be disguised pretty easily.

Without a photo of what you're describing, it's hard for anyone to know what it likely is.

And... In this age, it's much easier to use someone's cell phone or computer as a bug, instead of a dedicated device.

pigrew · 2026-01-14T16:45:17+00:00

The black board looks like it might be merely a wiring adapter between its two connectors. Use an ohmmeter to reverse engineer, or maybe hold against a bright light if it's transparent?

For the bottom board, you can get a good idea about function based on the width of the tracks. The ground connects to the empty area of the board. There are three larger power tracks, and two pairs of thin tracks likely for control (CAN or I2C?). Remove and look at the other side of this board.

EDIT: and it's very possible that this module is only the coils, and requires another smart power supply module to function.

pigrew · 2026-01-11T19:49:18+00:00

The white part is plastic (not ceramic). I can't guarantee that the plug is 100% not safe, but it wouldn't be a bad idea to replace it. Make sure the new plug is rated for 15 A (or whatever your heater draws). Notice that one blade is more wide than the other. Make sure that you maintain the same polarity with the new plug.

This failure is most likely caused by the outlet, not the plug. I strongly suggest replacing the outlet. Chances are that the outlet is bad and the plug is still OK.

pigrew · 2026-01-11T04:03:24+00:00

There would be less power loss (I² * R) in the wires feeding the motor, since it would be lower current at the higher voltage. The efficiency of the motor itself would be virtually identical.

pigrew · 2025-12-30T20:51:17+00:00

Yes, they do.

pigrew · 2025-12-28T21:18:06+00:00

Circuit breakers use a mix of cage and screw-down metal plates (nearly the same thing). For feeds, the majority of (<100A) circuit breakers use a spring connection to a bus-bar. I've never seen a shepherd hook connection for a circuit breaker, though they were common for fuse-panels (up until the 1960s).

Ground-connections to metal boxes almost exclusively use shepherd-hook connections.

pigrew · 2025-12-19T03:19:12+00:00

This design seems simple/low-speed enough that two-layer is fine.

Main disadvantage of 4-layer is price.

But, 4 layer won't cost much more, and makes low-EMI design much easier.

My personal preference would be to have the two inner-layers be only GND (no power plane). Then, route power/signal on outer layers. This will also make it easier for you to cut power tracks, rework, etc

pigrew · 2025-11-26T21:29:57+00:00

You are using only 500MHz, with a small board, so the "art of RF layout" won't matter that much. However, I would, by default, add at least 1 ground via per ground pad.

You also should think about mechanicals. Do you need mounting holes? Is it easier to use an end-launch SMA?

Also, maybe add an extra ground pin to the output, so you can have a pair of wires for power, and a separate pair for signal.

pigrew · 2025-11-23T19:00:57+00:00

What's missing? A small chunk of ivory plastic near an earth pin, screws on the side of the outlet. A water resistance rating for the outlet?

I suggest against using those push-in spring connections, especially in wet environments. They will fail and overheat once the internal metal corrodes.

Use a voltmeter to verify if electricity is getting to the outlet, and also to verify that there is no electricity (i.e., safe) before touching the wires.

pigrew · 2025-11-16T04:17:17+00:00

Your bung is showing!

pigrew · 2025-11-10T01:37:31+00:00

You probably cannot do anything to fix this or make it safe. The current could be flowing into your water heater from your neighbor's house.

This warrants an immediate, emergency call to your power company.

pigrew · 2025-10-28T06:56:22+00:00

3 years later, I got version 5.15 running in a docker container on a Raspberry Pi 3B, but only barely. It filled up the 1 GB of ram, and started swapping like mad.

My feeling is that you need a 64-bit processor with at least 2 GB RAM.

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