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Tutorial - How To Use A Multimeter | about 2 years ago

One note on the 2/20/200/… range series.
Manufacturing cost is probably one issue, as noted. The other contribution, however, is that you get readings that are “three significant figures” across the scale.
If you have a slide rule handy (or, if not take a look at some log-log or semi-log graph paper) notice that the spacing around, say, 1.234 is about the same as around 0.987. It’s a reasonable practice, when counting significant figures, to disregard the leading digit if it’s a one for just that reason.
See also discussions of Benford’s law for how this phenomenon shows up in other places.

Product SEN-09623 | about 2 years ago

Just to follow-up on this …
Tagging a couple 6.8Ks to the SCL and SDA lines helps a lot to clean up the appearance of the I2C bus. There’s plenty of room to superglue a couple of 0805s to the soldermask and then add some “field change” 30 gauge wires to the processor pins and also to 3.3 V.
The issue with the magnetometer seems to be that it really, really wants a full power cycle or else it can get hung at a fixed value (32 in my case; don’t know if that’s universal). It wasn’t an I2C bus problem but I’m happier now that the bus looks right.

Product SEN-09623 | about 2 years ago

Very unhappy I2C bus, at least on this sample of one that I have here.
It looks like the board is depending on the 50K pull-ups that are internal to the magnetometer and that is way too much to run a 200 Kbps I2C bus. I’m seeing a rise time (standard 10%-90%) of more than 2 usec, twice the maximum for a even a “standard mode” 100 Kbps I2C bus.
The accelerometer (which shares the I2C bus) seems to be okay with it but the magnetometer isn’t talking. Maybe it’s dead but I suspect that tagging the SCL and SDA lines with 7.5K or 6.8K will do the trick.

Product DEV-00667 | about 2 years ago

Yes, it is. Well, only the crystal is removable; the socket is soldered to the board. ;–)
It’s the usual HC49/U or HC49/US thru-hole form-factor.

Product SEN-08942 | about 3 years ago

Those are the A/D readings assuming that the vane sensor is on the lower (grounded) side of a voltage divider with one of the resistors at the head of the columns on the top (Vcc) side, and that the A/D resolution is 8 bits.
E.g., for a north wind (33K ohms) and a 10K dropping resistor, 255 * 33K/(10K + 33K) = 196 counts. There’s certainly no requirement to use any of those resistor values but they’re quite reasonable.
It’s not the clearest data sheet I’ve ever seen. Not the worst, either. ;–)

Product SEN-08942 | about 3 years ago

The wind vane outputs are discrete, not continuous, with eight 45-degree sectors more or less centered on the compass rose. Different resistors are switched in-line for each sector. One caveat: the boundaries are not crisp and you may see an open or an overlap (with two resistors in parallel) for a few degrees around each sector edge.
Values in K-ohms:
N 33
NE 8.2
E 1
SE 2.2
S 3.9
SW 16
W 120
NW 68