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1  Using Arduino / Sensors / Re: RFID project, need some guidance on reading multiple passive UHF RFID tags on: Today at 12:47:14 pm
No. A half-wavelength at 915MHz is only 16.4cm.
2  Using Arduino / General Electronics / Re: Question about transistors on: Today at 12:46:03 pm
Some of us don't have Fritzing and don't want it. Could you post a screenshot?
3  Using Arduino / General Electronics / Re: Question about transistors on: Today at 12:12:23 pm
Nothing is attached.
4  Topics / Product Design / Re: Breath triggered LED light with piezo sensor on: Today at 11:07:33 am
Are you sealing your lips over the hole in the piezo case and blowing? If not, then it is responding to the sound of your breath blowing by the hole.

Yes, I'm sure it also works when you press on it. It still isn't the same thing. Put your oscilloscope on it, or connect it to an amplifier and listen to it.
5  Using Arduino / General Electronics / Re: Resistor value on: Today at 11:05:24 am
What did you have in there before you substituted  PN2222? Why did you substitute?

I agree with what rmetzner49 said.
6  Topics / Product Design / Re: Breath triggered LED light with piezo sensor on: Today at 06:25:53 am
You keep saying "breath sensor", but it really is a "noise of blowing sensor". It isn't detecting the moisture in your breath. Just making sure you know that.

As I said, simply removing a piezo from a case may actually make it less sensitive at picking up sound. There is a reason that microphones and speakers come in cases, to separate the front from the back to avoid having the sound partially cancel is the primary reason.

Seriously, just add an amplifier. A simple Op Amp circuit, or an LM386 audio amplifier.
7  Topics / Product Design / Re: DIY CNC? on: Today at 06:23:11 am
A decent drill press and a good selection of drill bits is much cheaper than a CNC mill.

The Shapeoko2 is reasonably priced:
http://www.inventables.com
8  Topics / Product Design / Re: Plastic Token Verification Purpose on: Today at 06:17:31 am
You could do paper tokens using QR codes as a serial number system, with the actual data on the computer.
9  Topics / Product Design / Re: Breath triggered LED light with piezo sensor on: Today at 06:06:40 am
Using a piezo without a case won't necessarily make it more sensitive.

What you need is a preamplifier. Even an LM386 amplifier should work for this.
10  Using Arduino / Sensors / Re: Strange output using 2 Ultrasonic Rangefinders on: Today at 06:03:47 am
What happens if you read only one?
11  Using Arduino / Sensors / Re: Multiple Line followers on: Today at 06:00:40 am
What do you mean by "line follower"? That phrase usually means the entire robot.

Part number? Link?
12  Using Arduino / Sensors / Re: How many trigger sensors can I have? on: Today at 05:58:06 am
Urgh. I hate that kind of input.

The Arduino's analogRead is rather noisy. You'll need to add a 0.1uF from Aref to ground, do some averaging of the signal in software, and don't use too many resistors on one input. That 10 bits is really more like 8.5 ENOB (Effective Number of Bits), and the numbers are also affected by changes in the 5V line.
13  Using Arduino / Sensors / Re: RFID project, need some guidance on reading multiple passive UHF RFID tags on: Today at 05:54:23 am
915MHz does not use NFC, so I'm uncertain why you mention it. UHF RFID is electromagnetic in nature, with fractional wavelength antennas.

Digital interference like that is going to be destructive.

You need to either use a very directional antenna on the reader (it takes a lot more than just a transistor fed a 915MHz signal and it -doesn't- use a magnetic loop) and tags spread out physically so that you can select them by aiming the antenna at them, or use smart tags that will wait to respond until they've been polled.
14  Using Arduino / Sensors / Re: Help - SMD temperature sensor on: Today at 05:44:57 am
Analog or digital output? You are going to have a hard time using such a high accuracy sensor if you are using analogRead, as it is only 10 bit (really more like 8.5 ENOB).

Here are some from TI's website, culled to +-1C, surface mount, digital output:

http://www.ti.com/lsds/ti/sensors/temperature-sensors-products.page#p2033max=0.33;1&p2954=SOIC;SOT-23;SOT;SSOP&o7=Digital Output&p158=SPI;I2C&p1130=0.17;1.69
15  Using Arduino / General Electronics / Re: Trouble powering arduino and amplifiers from the same power source on: September 30, 2014, 10:59:54 pm
Yes, removing the 10k pullup and using a higher value pulldown on the /shutdown pin is to save battery power.
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