August 27, 2010
about a year ago
“A similar sensor that measures IR intensity in mW/cm2 would be pretty cool too!”
A plain silicon solar cell + IR-pass filter would get you into the near IR.
The curve for the UV index measurement looks like it admits the wavelengths for UV-B and UV-C and does not provide for any measurement of UV-A. The response curve for this sensor looks like it will sense UV-A and UV-B but not UV-C. The UV-A sensitivity is probably a good thing because it could lead the user into being extra cautious about getting too much sun. The lack of UV-C would in theory cause a bias in the opposite (not careful enough) direction. But that depends on how much UV-C one actually has a chance of being exposed to (Wikipedia says: “completely absorbed by the ozone layer and atmosphere”). My gut feel is that this sensor will actually be pretty well suited for the job of helping us avoid UV exposure even if it won’t support numerically accurate UV Index calculations.
about a year ago
Found the issue - jumbled organization of the product categories at HK. And the flat 2D CAD drawings there provided that confirmation. :-) (couldn’t resist…)
We all appreciate SF’s efforts at documenting the mechanical aspects of the products. I’ve seen in the comments sections that it’s been a work in progress for some time.
Just a note to everyone to be careful about servo size names. What SparkFun calls a Standard servo is what Hobby King calls an Extra-Large. The Standard servo I bought from Hobby King is unusably small inside this mounting plate. The bottom line is that dimensions need to be checked carefully before ordering because an item name can be misleading. Between HK and SF I’m not sure who’s using nonstandard terms.
While we’re on the topic of documentation, Having Sketchup drawings alone for mechanical drawings is inconvenient. Yet another application to load onto the several PCs I use to access this site. PDFs work just fine for me and it would be good customer service to make those available too. Thanks for listening.
about 2 years ago
A couple of things to keep in mind…
Electrical: pH sensors have impedances on the order of 10 gigohms to 1 teraohm. The supplied PCB might kill the low voltage signal due to surface conduction if the solder flux wasn’t cleaned well or if you spilled some gack on it. Most pH meters bring the signal pin in on teflon standoffs and lift a leg of the IC dead bug style so that the signal never even touches the PCB. Very few op-amps have a high enough input impedance to handle pH signals. Think of these sensors as being a zero-current reference battery with a pH-dependent output voltage.
Chemical: The best storage solution in between uses is a pH 4 buffer with a lot of potassium chloride added. Not sodium chloride. The cell uses potassium chloride in it’s internal reference cell and in the “salt bridge” which makes the ground connection into the water sample being tested. pH membrane glass is (barely) conductive to a current consisting of hydrogen ions (not electrons). This storage solution keeps the glass membrane primed.
Physical: this sensor is probably not compatible with direct soil measurements. The connection will be poor and you can easily break the thin bulb. If you’re careful not to poke any gravel or twigs into the glass you could try mixing up some mud using deionized water and measure that.
about 3 years ago
After laying out a board for the previous revision of the Pro Mini I thought it would be nice to get all those other pins beyond the dip pattern into the Eagle footprint. I used flying leads for DTS, SDA and SCL to connect onto the PC board. Nobody would be forced to put header pins into the non standard locations, but it wouldn’t really be difficult either.
No public wish lists :(
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