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16  Using Arduino / General Electronics / Re: What's this peice called? on: July 23, 2014, 09:05:20 pm
That is a capacitor. It looks like, by placement, it may be a bypass capacitor on the 3.3V regulator. Your best bet is to ask Adafruit.

See page 44 of the PDF, it has a schematic of the board. Perhaps you can trace some of the PCB traces back and figure out which capacitor this is.

https://learn.adafruit.com/downloads/pdf/adafruit-cc3000-wifi.pdf

Wow, that is freakishly faded.

Bottom left corner of this PCB pattern, it does appear to be one of the bypass capacitors. One end to ground, the other end to the tab on the regulator.
17  Using Arduino / General Electronics / Re: Spent 2 days trying to get TIP 120 fan control to work on: July 23, 2014, 06:41:58 pm
Do you really need 0rpm? The airflow is going to be indistinguishable from random air movements even at a few hundred RPM.
18  Using Arduino / General Electronics / Re: Linking audio amp problem. on: July 23, 2014, 06:40:25 pm
An audio amp is essentially an Op Amp but with the negative feedback internal, the input ground referenced, and the output designed to drive a low impedance.

There are some potential problems with using an audio amp as a small signal amplifier. One is noise. The amount of noise voltage on the output that is inaudible in an 8 ohm speaker may be intolerable when used as a small signal amplifier, especially when followed by another amplifier. The outputs may be a bit unstable when run with no or a high impedance load. The frequency compensation is suited to an audio amp, and may result in decreased gain above 20kHz.

19  Using Arduino / General Electronics / Re: Linking audio amp problem. on: July 23, 2014, 05:19:34 pm
http://www.siongboon.com/projects/2008-04-27_analog_electronics/op%20amps%20for%20everyone%20third%20edition%202009%20(Texas%20Instrument).pdf

Or by the 4th edition:
http://www.amazon.com/Op-Amps-Everyone-Fourth-Edition/dp/0123914957

20  Using Arduino / General Electronics / Re: homemade pulse sensor for detecting hartbeat? on: July 23, 2014, 05:17:05 pm
The article gets a few things wrong and isn't very complete.

That is not a photodiode, it is a phototransistor. I'm going by what Radio Shack's website says about that pair:

http://www.radioshack.com/product/index.jsp?productId=2049723

What parts are -you- using? The most critical parts are in that set of IR LED and IR phototransistor. Any substitution of the phototransistor is likely to prevent it from working.

Can you measure the voltage at the bottom of the 39k resistor with a fingertip on top of the LED and phototransistor? It should be somewhere between 1 and 5V when your finger is on top of the LED and phototransistor.

Note the symbol and orientation. Rely on the literature that came with the pair for the orientation, if it is different from this:

21  Using Arduino / General Electronics / Re: Linking audio amp problem. on: July 23, 2014, 03:50:43 pm
I mentioned this, too.

An LM324 or LM358 should work.
22  Using Arduino / General Electronics / Re: Spent 2 days trying to get TIP 120 fan control to work on: July 23, 2014, 03:47:15 pm
And....
23  General Category / General Discussion / Re: How to begin? on: July 23, 2014, 01:29:38 pm
What are Kirchoff's voltage and current laws? What is a Thevenized circuit, and a Nortonized circuit, and why do we use them? What are the major differences between BJT and MOSFET?

If you really want to learn electronics, get a few general purpose shields with protoboard.

Also, get a large protoboard. Build some stand-alone circuits.
24  Using Arduino / General Electronics / Re: ADC false readings on: July 23, 2014, 12:44:26 pm
It is good practice to add a 2.2k resistor in series between the current sense resistor and the non-inverting input of the Op Amp. In that way, you compensate for input bias current. You can also then add a capacitor from the noninverting input to ground to act as a lowpass filter.

Have you tested this Op Amp to see how it responds near the ground rail? So-called "rail to rail" Op Amps often will only be good down to a few 10s of mV from ground, then not behave well.

Personally, I'd add a small negative supply voltage and some zero calibration.
25  Using Arduino / Project Guidance / Re: Encoder to velocity project on: July 23, 2014, 12:06:43 pm
OK, so what you want to calculate is RPM?

Don't use delay(). That is a horrible little command.

http://playground.arduino.cc/Main/ReadingRPM

You may also use micros() in there for better accuracy at higher RPMs.

Have you tried just searching for
arduino tachometer
or
arduino rpm

http://www.pyroelectro.com/tutorials/tachometer_rpm_arduino/

26  Using Arduino / General Electronics / Re: 110V detection on: July 23, 2014, 12:01:53 pm
I agree with Docedison. Simple, cheap, safe, tough. Don't forget that an NE2H requires a current limiting resistor, too. 33K is usually used for 120Vac. For 240Vac, 100k is about right.

I lay it flat on the photocell, placed so the leads of the neon bulb are 90 degrees from where the leads of the photocell come off and "flat" so the space between the electrodes faces the photocell. So it doesn't shade itself.
27  Using Arduino / General Electronics / Re: ADC false readings on: July 23, 2014, 11:52:42 am
What about the current sense resistor? Both ends can't be grounded.
28  Using Arduino / General Electronics / Re: ADC false readings on: July 23, 2014, 11:07:42 am
R2 and R3 are grounded, through multiple wires. The non-inverting input of the Op Amp is grounded. You wouldn't be getting 1.3V with it wired that way. I'm not sure what it would be, but it wouldn't be meaningful.
29  Using Arduino / General Electronics / Re: ADC false readings on: July 23, 2014, 10:13:15 am
You need to review and correct your schematic, it has connection points that should not be there.
30  General Category / General Discussion / Re: How to begin? on: July 23, 2014, 09:09:43 am
How are  you going about improving your skills with electronics?
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