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46  Using Arduino / General Electronics / Re: Reading voltage - Product already exists?? on: July 09, 2014, 06:11:15 pm
As stated the standard arduino Uno board has 6 analog input pins capable of reading any voltage in a 0 to +5vdc range. No negative voltages allowed and no voltages over +5vdc. If you need to read a voltage higher then +5vdc then you need to scale the external voltage down usually using a two resistor voltage divider so the resulting voltage cannot climb above +5vdc. You can then rescale the voltage back to it's 'real' value in software.

 So what is the DC voltage range you need to measure?

47  Using Arduino / Installation & Troubleshooting / Re: Installing bootloader on Mege2560 on: July 09, 2014, 09:27:31 am
A lot of AVR ICSP programmers can't handle the larger flash memory size of the mega2560. USBtiny is one of them that can't.

I too recommend using Nick's bootloader sketch, it's proven and the  most informative as you interface with it using the serial monitor.

48  Using Arduino / Programming Questions / Re: Atmega328p doesn't work under 2.7v on: July 08, 2014, 06:57:31 pm
Hi.  I used to use my atmega at 2v running 8 mhz and internal oscillator....

I formated my pc and after that when I try to run the atmega328p it stop work when voltage goes under 2.7.

How could I get it back to work using 1.8v?

Do I need a special bootloader or a special board at boards.txt?

Tks a lot

 I suspect you will have to look at the Extended fuse byte value used when a chip is setup to run with the arduino. There are some bits that control BODLEVEL (brown out detector) which determines at what level Vcc decreasing will cause the chip to stay in a reset condition. The choices are  typically 1.8, 2.7, and 4.3.
The 328P datasheet is the best reference to work this out.

49  Using Arduino / Project Guidance / Re: Accuracy analog input. 9v batt on: July 08, 2014, 12:13:31 pm
It doesnt work that well.

I connected a 9v battery to the power jack in the arduino and the analog readings is not accurate to the voltage.

If i have a 20 mA signal thats messeure 5 volts over the resistor 250ohm i dont get maximum value that is 1023 from the Arduino.
When i messure between the gnd and 5v pin on the arduino i have 5.17 volt.

What can i do to make the reading more accurate

 If you know that the on-board +5 vdc voltage regulator has an output voltage of 5.17, then use that value with the mapping function to get a correct analog voltage scaling. Best to use millivolt scaling to get better resolution.

int value = map(analogRead(A0), 0, 1023, 0, 5170);  //results in millivolts
50  Development / Suggestions for the Arduino Project / Re: Breaking away from a PC on: July 07, 2014, 07:03:09 pm
The Arduino developers already struggle with keeping the Arduino IDE current on Windows/Linux/Mac, adding another platform to support the IDE & tool chain seems a bridge too far to me. But if a 3rd party wants to take a try at it, all the power to them. When they prove out the concept then maybe the Arduino developers could take a look at it. I would rather hate to have to write a sketch on a small smart phone screen, but maybe others would?

51  Development / Other Software Development / Re: Documentation update request - analogRead() on: July 07, 2014, 06:47:52 pm
The AVR analog input pins work best when the output impedance of the signals wired to a analog input pins is 10K ohms or less. Another method for handling higher impedance signals is to wire a .1 ufd cap from the input pin to ground, that will lower the impedenace that the internal ADC 'sees'.

52  Using Arduino / Project Guidance / Re: AREF pin setup on: July 07, 2014, 04:31:22 pm
The other caution you should consider is if your external +5vdc sensor power is ever active but the arduino supply is turned  off it's possible damage could result from high ref pin current.

53  Using Arduino / General Electronics / Re: External power to boards. on: July 04, 2014, 09:14:28 pm
I have noticed on the boards I have there are +5 pins.

These are usually for "outgoing" power to things.

But I am maybe getting a NANO and its only supply is from the USB port.

Adding a USB connection to my project to supply power to the NANO will be annoying.
So I was wondering if I can feed power to it on the +5 pin?

Yes you can. Also a nano has an on-board +5 vdc voltage regulator feed from the Vin pin, which can be like 7-12vdc. So you have options.

54  Using Arduino / Project Guidance / Re: Reading antilock brake signals on: July 03, 2014, 05:11:32 pm
Yes, this kind of sensor usually interfaces to a comparator chip to convert it to a clean digital signal usable as a digital input signal for an arduino. After that its just measuring it's frequency/period. Rather then using a frequency counter type sketch and considering that you need to read two of these signals I would look into using the pulseIn() function to read the two signal and do your comparison.
  As an aside there is a related application that you are working on used on my 2000 Buick. The ABS signals are also used to compare wheel speed of all four wheels and signals that there is a low tire pressure if one reads different then the other three. It works very accurately, detecting low pressure on a tire that I can't see visually but proven correct with a pressure gauge. So what you are trying to do is certainly doable.

55  Community / Bar Sport / Re: The Cracked Pot on: July 03, 2014, 10:39:43 am
Reminds me of the 'glass half full/empty' definition:

Optimist, the glass is half full
Pessimist, the glass is half empty
Engineer, the glass is twice as big as required
Scientist, the glass is always full of something

56  Using Arduino / Programming Questions / Re: 1023 value in reading analog voltage on: July 02, 2014, 02:54:11 pm
Yep, the topic that will never die.  smiley-wink
57  Using Arduino / Project Guidance / Re: AtMega328p to board.. on: July 02, 2014, 02:48:56 pm
thanks you all..that mean i dont need buy programmer USBasp??? and just use the arduino to program he ATmega?

58  Using Arduino / Microcontrollers / Re: Atmega1284p Bootloader Problems on: July 02, 2014, 12:35:36 pm
Sounds like it could be that the 'Full Swing Crystal Oscillator' fuse byte option might help you. Change the  low byte fuse value to D6 and see if that helps. It was/is a noise problem with lots of standalone 1284P boards coupling noise between clock and serial input pin. Many found their serial com problems with 1284P completely cured when going with the 'full swing' option.

59  Using Arduino / Project Guidance / Re: AtMega328p to board.. on: July 02, 2014, 12:21:48 pm
60  Using Arduino / LEDs and Multiplexing / Re: LEDs in Reverse Bias on: July 02, 2014, 12:20:51 pm
Be very careful with an reverse bias experiments, common 20 mA leds tend to have a maximum +5vdc reverse bias voltage before breaking down and unless current limited can be destroyed.

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