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March 12, 2008
News - Voltage Divider App for i…
about 6 years ago
Well that’s all well and good, but you know what you really need? See what you’ve got in front of you is a pile of resistors of various values, and what you need is a particular output on your divider. So if you could enter all the values of your resistors, and have the app select the pair that most closely matches your requirements, then you might have something that’s actually useful.
Also, the iphone has a camera right? So how about something that will let you photograph a bunch of resistors and figure out what value / tolerance they are from the color bands.
about 7 years ago
So I finally got around the checking the LED voltage, and it is only being driven at about 1mA - not enough to really get much brightness. I’m going to mod my board and connect the LED logic pin directly to the 300 ohm current-limiting resistor, bypassing the transistor and the resistor on the transistor’s base. This should give me 10mA or so (maybe less) and if your micro can source 10mA on a logic pin (the freescale micro I’m using can), then you should be fine.
about 8 years ago
I think I’ve found a problem with the design of this board, and an explanation for your low brightness. With the LED being driven by the transistor, and with the voltage drop across the transistor, we’ll probably only be seeing about 2.6v across the resistor and the LED. I have used the avago color sensor without this board & I’ve had the LED running at about 6mA & it’s very bright indeed. With this board the LED will probably be drawing less than 1 mA ( I haven’t measured it, but I will soon ) and so we’ll be seeing about a tenth of that (judging by fig 13 in the sensor’s datasheet).
So I think this board needs a redesign. I was driving the LED directly from a logic pin just using a current-limiting resistor and I had no problems (and a very bright LED!).
about 8 years ago
this motor: http://www.mabuchi-motor.co.jp/cgi-bin/catalog/e_catalog.cgi?CAT_ID=fc_130rasa seems to fit the bill perfectly. Runs at 12v, with a 0.84A stall current and seems to be exactly the right size. If only I could actually buy one from somewhere!
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