TechExplained: Bluetooth Channel Sounding

Posted under Back to Basics, Educational, Technology on December 8th, 2024 by

Slightly advanced topic for today. It’s a new little specification in the new Bluetooth 6.0 standard which I think is interesting. Bluetooth Channel Sounding is a feature that enables precise distance measurement between Bluetooth devices.

Unlike earlier methods relying on signal strength (RSSI), Channel Sounding uses phase-based ranging and round-trip timing. These techniques leverage phase & frequency of radio BLE waves at 2.4GHz to calculate distances with potentially a few tens of centimeter precision even with large 50m+ line of sight ranges.

Here’s how it works: one BLE device sends a signal with a known phase and frequency. The second device echoes the signal back, maintaining phase continuity. By comparing phase shifts and factoring in timing, the system calculates the distance between devices. This will effectively give you much better precision than the older RSSI techniques. BLE 5.1 had introduced direction finding in Bluetooth based on the angle of arrival and angle of departure. However, the implementation issue was that you needed multiple antennas on either the transmitter or receiver end. Channel Sounding can work with a single antenna on each side making implementation easier.
Why does this matter? Think of the Locate Me feature in your phone or key trackers. With Channel Sounding, the search goes beyond “it’s nearby” to pinpoint exact locations, even in complex environments. The technology also enhances digital keys, ensuring your car or door unlocks only when you’re within a precise range, significantly improving security. It will have applications in indoor navigation, asset tracking, VR controller tracking etc. I very well see Apple ditching UWB tech in their air tags in the future for this tech as airtags do contain an additional BLE chip. Your future phones will definitely have this feature.

Exciting times ahead for BLE! If you’re curious to dive deeper, a fantastic white paper has recently been published on the official Bluetooth website. It’s a great read that keeps the concepts clear and jargon-free, definitely worth checking out!

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Back To Basics: PCB Test Points

Posted under Back to Basics, Educational, Product Design, Technology on December 1st, 2024 by

Let’s talk about something simple yet incredibly crucial – PCB test points. If you’ve ever wondered what those tiny little exposed pads scattered across a PCB are doing there, this one’s for you.

Test points are essentially designed spots on a PCB where you can easily connect probes or testing equipment during manufacturing for troubleshooting. Think of them as small entry points giving you direct access to the board’s inner workings without messing up the traces.

Why use them? Without test points, you’d have to solder wires by scratching off the solder mask. It’s OK for larger tracks but it’s a strict No-No for thinner ones. They can be used for functional board testing during production, debugging in your development cycle, or even repairing/diagnosing faults in the field. In production, you might use a test jig with spring-loaded probes or even use the fly probe technique to probe the test points to see continuity, measure voltage, or even inject voltage to see a response at another test point.

How do you design them? Good test points should be accessible and preferably all on the same side of the PCB. Placement and size matter, where it should be accessible for probing and the size larger than the probe tip. If in a pinch, you can even use a PCB via as a test point if it’s untented(solder mask removed), although I won’t recommend it as a sharp probe can damage a via. The only place you need to be super careful is when you are adding vias for high-speed signals. I try to not provide a test point and usually try to probe them at the IC/connector end because adding a test point can introduce a stub or disturb the spacing in high-speed differential lines. If absolutely needed, I will stagger them in a way to not affect the spacing between them or expose the solder mask.

Check images above for different types of test points. These are metal parts that can be soldered on the PCB to give a place for a probe to hook onto.

Test points might not get the spotlight as some other things on the PCBs, but they are as crucial as anything else on the board. Any PCB manufacturer will attest to that.

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