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46  Using Arduino / Installation & Troubleshooting / Re: Voltage level on Serial pins on: April 11, 2014, 08:22:43 am
If you are reading a series of pulses with a voltmeter you will likely see just the idle state (LOW).  To read the voltage of the pulses you would typically use something like an oscilloscope.  If your data is getting through then the voltages are within spec.
47  Using Arduino / Displays / Re: What am I overlooking? Why isn't Bar printing? on: April 10, 2014, 10:15:53 pm
Do you mean this part:
Code:
    lcd.setCursor(12, 0); 
    lcd.print(mpxValBar, DEC);
    lcd.print("Bar");

Perhaps there is not enough room in the last four characters of the line to put the number and the word "Bar"?
48  Using Arduino / Programming Questions / Re: Boat autopilot - PID not centralizing rudder. on: April 10, 2014, 10:07:09 pm
Re-tune your PID.  Sounds like one of the parameters is way off.

My understanding is that you start with all parameters 0 and the crank up the P parameter until you get a fast response with minimal overshoot.  Then increase D to eliminate the overshoot without slowing the response too much.  Then increase I to eliminate offset (where it settles close to but not on the desired setpoint).

There is also a PID auto-tune library that might help.
49  Using Arduino / Sensors / Re: Problems with Ultrasonic Range Finder - Maxbotix LV-EZ1 on: April 10, 2014, 09:52:54 pm
I am still confused on how to implement the pin I want to use for RX in the code you wrote for the example pin 5.  Could I use pin 11 (since it is one of my empty pins) instead of pin 0?

Yes.  If you are using an UNO or MEGA just look up the pin number in the spreadsheet I pointed to.  That will tell you which port and which pin.  Bits are numbered from the right.  Bit 0 is the rightmost bit.  Bit 7 is the leftmost bit.  1 == HIGH and 0 == LOW.
50  Using Arduino / Project Guidance / Re: MAX 31723 Temperature Sensor Using SPI Protocols on: April 10, 2014, 04:21:44 pm
If you look at Figure 10. (SPI Multiple-Byte Burst Transfer) it shows the SCLK stopping between bytes.  This is normal for SPI.  Are you sure you have SPI selected (SERMODE connected to Vdd, not GND)?
51  Using Arduino / Project Guidance / Re: MAX 31723 Temperature Sensor Using SPI Protocols on: April 10, 2014, 07:14:51 am
Looks like they use CE for the SPI Slave Select but the logic is reversed.  To send two bytes:
Code:
   digitalWrite(CE, HIGH);
   SPI.transferAddressByte);
   SPI.transfer(DataByte);
   digitalWrite(CE, LOW);
52  Using Arduino / Project Guidance / Re: INTERFACING GSM SIM 900 WITH LEONARDO. on: April 10, 2014, 07:08:28 am
where shud i include that line to configure COMMAND MODE.

Before you send an AT command.
53  Using Arduino / Project Guidance / Re: How to determine position of GY521 in cartesian cordinates . on: April 10, 2014, 07:04:15 am
i have computed pitch, roll , yaw. but i don't know what i must do continuous?

To draw the leg, start with a fixed point (either the hip or the toe) and draw segments the length of each foot part in the orientation you calculate from the sensors.
54  Using Arduino / Sensors / Re: Problems with Ultrasonic Range Finder - Maxbotix LV-EZ1 on: April 10, 2014, 06:59:37 am
I am sorry smiley-confuse I am still learning Arduino programming and I did not get what the code meant in the last reply. Is there a way you could simplify what direct port addressing is and how to use the code you wrote?

Every I/O pin is represented by a bit in an 8-bit I/O port.  This spreadsheet:
https://spreadsheets.google.com/spreadsheet/pub?key=0AtfNMvfWhA_ccnRId19SNmVWTDE0MEtTOV9HOEdQa0E&gid=0
shows the mapping of pin number to port and bit for the UNO and MEGA.  By turning the bit on (HiGH) and  off (LOW) directly you can avoid much of the overhead of the digitalWrite() function.

See: http://arduino.cc/en/Reference/PortManipulation
55  Using Arduino / Project Guidance / Re: INTERFACING GSM SIM 900 WITH LEONARDO. on: April 08, 2014, 07:59:34 am
It looks like the SIM 900 is just echoing everything it sees.  Perhaps it has to be switched to Command Mode.  Often this is done with:
Code:
delay(1000);
Serial1.print("+++");  // Start command mode
delay(1000);
56  Using Arduino / Installation & Troubleshooting / Re: Arduino IDE will not start on: April 08, 2014, 07:50:05 am
Are you getting error message, If yes paste the sanp shot of it

On Mac OS X you can see some error messages by running the "Console" app.
57  Using Arduino / Installation & Troubleshooting / Re: Arduino IDE will not start on: April 07, 2014, 10:56:29 pm
The Arduino IDE is a Java program.  Perhaps there is something wrong with your installation of Java.  Might be time to look for an update.
58  Using Arduino / Project Guidance / Re: Setting SPI parameters in a library on: April 07, 2014, 10:52:57 pm
I have noticed that some libraries only set SPI parameters (mode, clock div, bit order) for their device from within the begin() function. How are users expected to use such a library and also use (in the same sketch) other devices that expect conflicting SPI parameters?

They aren't.  The library write was not expecting the SPI bus to be shared so they took the lazy route.  Fortunately you have the sources handy so you can correct the problem.
59  Using Arduino / Microcontrollers / Re: making a boarduino - having trouble uploading sketch on: April 07, 2014, 10:28:47 pm
Isn't the Arduino using the same FTDI chip to program?  I guess not...?
The Arduino UNO uses a small ATmega processor to do the USB-to-Serial job.

Is your DTR line connected to the Boarduino reset line via a capacitor?  If not you will need to do a manual reset.  Hold down the Reset button (add one if you left that out) and click on the upload button.  When the Receive LED blinks (add one if you left that out) release the Reset button.
60  Using Arduino / Sensors / Re: Problems with Ultrasonic Range Finder - Maxbotix LV-EZ1 on: April 07, 2014, 10:17:43 pm
Well, that is why I wanted to use the RX.  Maxbotix said to use it in this article: http://www.maxbotix.com/documents/LV_Chaining_Simultaneous_Operation_AN_Out.pdf.  The only problem is that I don't know how to pull the RX pin high for more than 20uS but less than 400uS. Do you know how to do this?

To be really sure you should use direct port addressing:
Code:
// Assume that the RX pin is connected to Pin 5 which is PORTD bit 5
// https://spreadsheets.google.com/spreadsheet/pub?key=0AtfNMvfWhA_ccnRId19SNmVWTDE0MEtTOV9HOEdQa0E&gid=0

// Fast equivalent of digitalWrite(5, HIGH); should take less than a microsecond
PORTD |= B00100000;

delayMicroseconds(20);

// Fast equivalent of digitalWrite(5, LOW); should take less than a microsecond
PORTD &= B11011111;
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