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16  Topics / Science and Measurement / Re: A/D converter on: April 01, 2014, 04:03:35 pm
Ohhh, I see what you mean now. Yup.

Pete
17  Topics / Science and Measurement / Re: A/D converter on: April 01, 2014, 01:17:30 pm
Yes, you would have to calibrate it to know what the fullscale voltage is and adjust the formula accordingly. If it can exceed that, I would submit it hasn't been engineered properly.

Pete
18  Topics / Science and Measurement / Re: A/D converter on: April 01, 2014, 12:33:16 pm
It depends what the formula is used for. The resolution is Vref/1024. But if what is needed is a fraction of full scale (0.0 to 1.0) then Vref/1023.  is appropriate.
For example, if Vref is 5V, then the resolution is 4.88mV per bit.
But if you want to convert an ADC reading to a voltage then you need (5*Vref)/1023. so that a reading of 1023 (full scale) gives you (5*1023)/1023. = 5V

Pete
19  Using Arduino / Programming Questions / Re: Weird little math problem on: March 31, 2014, 12:55:02 pm
Integer division truncates.

Pete
20  Using Arduino / Programming Questions / Re: Weird little math problem on: March 30, 2014, 09:43:32 pm
Code:
target_rpm = ((8000/1023)*potvalue) + 1000;
That's not a good solution because 8000/1023 is 7 so it reduces to 7*potvalue+1000
If you want better precision you have to do a long multiplication. I think this will do it:
Code:
target_rpm = ((8000L*potvalue)/1023 + 1000;

Pete
21  Using Arduino / Project Guidance / Re: Smallest Arduino which can play WAV files and read values from sensors on: March 29, 2014, 11:07:04 am
The Teensy 3.1 is a 3V3 device with 5V tolerant digital inputs but the analog pins are 3V3 maximum (this might complicate connection to the accelerometer if it is a 5V device).
It does not have a 5V output pin. Its DC input must be 3.7 to 5.5 volts so if you supply it with 5V that can also be your 5V supply to other devices. It does have a 3V3 regulated output @ 100ma maximum - the audio board also uses this which will reduce the 100ma but I don't know by how much.
The audio board has a headphone jack and a uSD socket already populated. If you need a volume control pot or access to the line-in or line-out pins you have to add those yourself.
There would still be 4 free ADC input pins and several digital pins free on the edge of the Teensy 3.1 board when the audio board is connected but there are several others, either as through-hole pins in the interior of the board or as pads on the bottom of the board.
If you are unsure of anything it would be best to ask in the Project Guidance forum at:
http://forum.pjrc.com/forum.php

Pete
22  Using Arduino / Project Guidance / Re: Smallest Arduino which can play WAV files and read values from sensors on: March 28, 2014, 05:52:42 pm
Quote
It [Teensy3.1] can do stereo high quality audio.
The high quality audio is produced by an optional audio board http://www.pjrc.com/store/teensy3_audio.html

Pete
23  Community / Bar Sport / Re: Rothschild the reason for mh370 downing?!?! on: March 28, 2014, 11:00:32 am
There's nothing like waking up to a good conspiracy theory in the morning.

Pete
24  Using Arduino / Programming Questions / Re: Having trouble interacting with the Bleep drum. (Moved from General Electronics) on: March 27, 2014, 01:28:01 pm
The pulse is only going to be a few hundred nanoseconds long and might be too short for the hardware to "see" it reliably.
Try adding a delay after you set the pin LOW:
Code:
  delayMicroseconds(500);

Pete
25  Topics / Science and Measurement / Re: CO2 ppmv & ppmw math on: March 25, 2014, 05:04:05 pm
The wiki page on Henry's Law says that the law does not apply when the gas reacts chemically with the solvent and gives the specific example of carbon dioxide and water which form carbonic acid. So you can't use Henry's Law.

Pete
26  Using Arduino / Storage / Re: PROBLEM: Dynamic filename creation with SD card on: March 25, 2014, 03:51:51 pm
That's exactly what I said yesterday.

Pete
27  Using Arduino / Networking, Protocols, and Devices / Re: 1000 Arduinos cluster networking on: March 25, 2014, 03:42:15 pm
You could have several independent I2C busses if you use one or more I2C multiplexer chips.

Pete
28  Using Arduino / Project Guidance / Re: want to use azimuth with adruino on: March 25, 2014, 09:47:30 am
How are you rotating the antenna and where is it?

Pete
29  Using Arduino / Storage / Re: PROBLEM: Dynamic filename creation with SD card on: March 24, 2014, 09:57:28 pm
The filename on an SD card can only be 8.3 format. Even if t_year is 2 chars you are generating a 10.3 name.
I'd also suggest that you put the year before the month in the filename so that a directory listing will have the files in the proper order.

Pete
30  Topics / Science and Measurement / Re: CO2 ppmv & ppmw math on: March 23, 2014, 09:47:30 pm
I don't see how you can relate the concentration of CO2 in air to the concentration of CO2 in water. In particular, I don't see how you can differentiate between the "CO2 bouncing out of the water" and the CO2 already in the air.

Pete
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