Probing Signals: Snooping an I2C Bus on a Tiny Surface-Mount QFN Part

RE: Probing Signals: Snooping an I2C Bus on a Tiny Surface-Mount QFN Part

DAB — Sun, 29 Oct 2023 18:08:16 GMT

Yes, it makes you want to return to DIP circuits.

They were so easy to access and debug.

RE: Probing Signals: Snooping an I2C Bus on a Tiny Surface-Mount QFN Part

genebren — Sun, 29 Oct 2023 15:26:00 GMT

Another great blog topic. This gives me some great tips to try out in future projects.

I add a lot of flying leads to my early prototypes in order to attach test equipment to assist in the coding and debug processes. I tend to use Kynar wires attached using vias if possible, or by removing resist and soldering to traces. I like to run the wires to headers at the board edges, so that I can quick disconnect the board if I need to re-work the board.

The headers make it easy to attach scope probes or dupont connectors to route signals to instruments or even protoboards.

RE: Probing Signals: Snooping an I2C Bus on a Tiny Surface-Mount QFN Part

beacon_dave — Sun, 29 Oct 2023 12:06:05 GMT

It looks like you can get pogo test pins down to that sort of size, so could perhaps push them through a PCB footprint to get them aligned with the pad pitch.

Elastomeric connector to a breakout PCB is another possibility, more universal but not as hard wearing.

RE: Probing Signals: Snooping an I2C Bus on a Tiny Surface-Mount QFN Part

michaelkellett — Sun, 29 Oct 2023 09:37:42 GMT

As part of the Picoscope Road Test a while ago I received the Probe Positioning System:

[mention:46b8f258adb7442cad2e7b1f7eddcff8:f7d226abd59f475c9d224a79e3f0ec07]

I did quite like it but it isn't compatible with all scope probes and is quite pricey. (It won't work with Picos excellent cheap probes which I use for every day work quite often. It's so heartbreaking when you wreck a £300 probe by cooking it with a hot resistor.)

I have seen cheaper knock offs in the usual places.

I think your homebrew system is pretty good.

When I design boards (even for mass production) I try to make key signals accessible for debug. But that doesn't work for third party boards.