RE: Sixth Sense - Sensor Circuits - GraffitiBot blog 3

DAB — Mon, 07 Jan 2019 21:23:25 GMT

Nice design. I will have to keep this idea in mind if I need this type of circuit.

DAB

RE: Sixth Sense - Sensor Circuits - GraffitiBot blog 3

kulky64 — Mon, 07 Jan 2019 19:05:14 GMT

Hi, I have several notes to your design:

- You goofed up Eagle part for the KMT32B magnetic angle sensor. I assume you created your part according to Figure 1 in the datasheet. But this figure refers to pinout of the SO8 package. You want to look at pin assignment table for TDFN package on page 5 of the datasheet. With this error you have basically flipped the role of excitation and measurement points of the Wheatstone bridges. I don't know if this part would operate under these circumstanes, but I would not rely on this.

- I would remove center solder pad underneath KMT32B. Recommended solder pad layout in the datasheet does not show this pad, so why risking shorts to this pad that are difficult to see once the part is soldered down?

- I don't think your circuitry around KMT32B would actually work (unless I'm missing something). Because if you provide positive excitation voltage from +3.3V source and you are creating negative excitation voltage from op amp output so that one of your measuring points is at +1.65V, then as the bridge is unbalanced to positive and negative values between measuring points, the op amp output needs to go few millivolts above (no problem) and below (this is problematic with single supply) GND potential to maintain constant value of 1.65V at S- as shown in the picture (excuse my crude MS Paint sketch created from one of your images).

[View:/resized-image/__size/475x428/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-6b563349-759f-4f5a-955d-ede4dde5d708/contentimage_5F00_190515.png:475:428]