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January 6, 2010
Product DEV-12081 |
about 3 months ago
Close - it’s isolation specifically for the HTU21D humidity sensor, but I’m sure the temp. sensor benefits too. The HTU21D datasheet recommends this pattern for ventilation slits, along with clearing copper layers (which has been done, based on the picture of rear of this pcb).
Btw, its not 100% clear based on the pcb picture, but it seems D6 may not be grounded (due to the gnd fill being pinched off by the through-hole connector). However, D6 is for neg. volt. protection on ‘RAIN’ and not critical to operation.
I’ve been considering putting together a weather station - this is a nice collection of sensors on one convenient card, may finally give it a try.
News - January Caption Contest |
about a year ago
Once I touch this with my soldering iron, Sparkfun will be MINE!! Fools! They never saw it coming! Bwahahahaha!
“Sparkfun Powers Activate!”
News - New Product Friday: MOAR … |
about a year ago
Another vote for the old format. The soldering station, tools, and other stuff seem more casual - more like the the environment your customers sit behind (except your’s is way cleaner).
The new format seems more like you’re a sales or marketing guy, not a hip hobbyist/maker/hacker. It also sorta reminds me of the people standing behind tables at Costco giving out free samples ;-)
Product KIT-10111 |
about 2 years ago
Yes - just saw this too (linked from new retail package). This isn’t a properly designed LED driver.
To drive an LED with a transistor, you use an NPN as a low-side switch (emitter grounded), or a PNP as a high-side switch (emitter to Vcc).
What this board does is use an NPN as a high-side switch. This is do-able, but not as shown in this design. You typically need >0.7 V across the base-emitter to fully saturate an NPN; this means you need >5V on the base for this to function properly.
For this reason, NPN’s (and N-channel mosfets) aren’t used as a high-side switch (without proper base/gate drive). As others' pointed out, this why you need to play with the resistor values in the lab to get these to light properly.
While there are plenty of good tutorials on using transistors as switches (high-side, low-side), unfortunately, this design keeps propagating. In addition to this card, the same circuit is also shown throughout the Make Electronics book, as well as other designs on the web.
While technically it works (assuming RED/GRN/BLU inputs are >>Vf of diode), it’s not the correct way to use an NPN as a switch.
No public wish lists :(