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16  Using Arduino / General Electronics / Re: Multiple serial devices on single port (one at a time) on: September 10, 2014, 12:20:03 am
They typically have a serial signal equal to Vcc when high. Vcc can be 3-5.5v and I usually give them 5.0v.

That doesn't really sound like a serial signal  to me.  Or perhaps it's just the way you expressed it.   Are these "serial" devices actually sending you serial ascii or binary data which you need a uart to read,   or just turning their output signal on and off like a thermostat ?
17  Using Arduino / General Electronics / Re: Maintaining water at 38°C on: September 10, 2014, 12:13:59 am

Lots of elements at all kinds of power output from 200W  to 4 kW and higher.   Run off mains power or 12V.  Starting at about $8.
18  Using Arduino / General Electronics / Re: How to alter a analog signal on: September 10, 2014, 12:07:46 am
Perhaps you need something like this

float pot_volts = 5.0*analogRead(A0) /1023.0  ;                             // or 1024.0  if you prefer.
float output_volts = ( pot_volts > 3.5 ) ? (pot_volts) : (3.5)  ;    // output volts will be the larger of pot_volts or 3.5
float output_countf = 255.0*output_volts/5.0 ;
int output_count = (int) output_countf ;
analogWrite( output_count );

And then you need some suitable hardware ( capacitor circuit )  to smooth the resulting PWM output to a constant DC voltage.
19  Using Arduino / General Electronics / Re: How to alter a analog signal on: September 10, 2014, 12:01:36 am
You need a robot arm to twiddle the knob attached to the pot.    That is what you seem to be asking for.

20  Using Arduino / Programming Questions / Re: [RESOLVED] Expected unqualified-id before 'else' error on: September 09, 2014, 11:50:53 pm
I don't know why you would use a macro to implement a long-winded function like that.    Your program will include that code at every instance in your code where you invoke your pinWrite( ) pseudo function.   If you called that function more than a few times,   you would very quickly run out of program memory.    And,  if execution speed is important,  as you seem to think it is,    there are several much faster ways to identify the correct pin, than those long switch statements.
21  Using Arduino / Programming Questions / Re: Time.h and arduino-mk on: September 09, 2014, 11:46:08 pm
The code was obviously written by someone who dislikes the idea that C/C++ arrays start from zero.    Probably a fortran programmer.
22  Using Arduino / Programming Questions / Re: "Basic" Programming Difficult on: September 09, 2014, 11:43:42 pm
I'd suggest stop burning your brains   and  buy, borrow or steal  an elementary programming textbook and work through it.    Or there are many free tutorials available on line.    This is better than wasting time doing random nonsense without knowing what you are doing.
23  Using Arduino / Programming Questions / Re: Mysterious "ghost definition" of a user-defined function on: September 09, 2014, 11:37:10 pm
boolean Close(Output,RepCheck)

This is invalid.   You need to specify the type or class of those function arguments.
24  Using Arduino / Programming Questions / Re: problem in loop and serial statement on: September 09, 2014, 05:37:00 am
How can you have "trunk" and "bonnet" ?
25  Using Arduino / General Electronics / Re: Why my arduino just give 1,2VDC on digital pin on: September 08, 2014, 02:41:51 am
You need a resistor connected between the transistor base and the ground.
26  Using Arduino / General Electronics / Re: DC DC inverter couple of questions on: September 08, 2014, 02:37:57 am
An inverter is usually a device that creates A/C.
27  Using Arduino / Programming Questions / Re: GPS NMEA data logging to SD card. Help needed on: September 08, 2014, 02:33:57 am
One approach is to copy each character sent from the gps into a char array ( it will need to be about 132 characters long ),    and then each time you get a new line from the gps,   copy the line of text to the file.

You can then copy those lines of text to your serial monitor on computer or anywhere else you like.   You can also check which NMEA string it is,  if it isn't one of the ones you want, you can just ignore it.

If you want to extract actual information from the lines of text,   then you need to deal with the formatting and parsing of the data lines.    This can be done if you have expertise,   which you probably don't.   Save yourself the trouble and use tinyGPS.

There is an issue with SD card files,  whether to open the file and leave it open,   or open and close it every time you right to it.   Both methods have considerable disadvantages.    Opening and closing the file for every single character is ridiculous,   opening and closing the file to write a whole line of text is a more reasonable plan.
28  Using Arduino / Programming Questions / Re: Strange Compile problem with Adafruit i2c sketch on: September 08, 2014, 02:28:17 am
Did you restart the IDE right after you originally copied the library files ?

The IDE only looks at library files when it starts up.    If you copy library files and then try to compile something right away,  it won't work.   You have to close the IDE and restart it,   to make the library files get read.

That may be your problem.   The issue with the 32 and 64 may be just a red herring.
29  Using Arduino / Motors, Mechanics, and Power / Re: Best 12v dual motor drive for the job on: September 07, 2014, 10:11:34 pm
Is the torque value before or after the gearbox ?
30  Using Arduino / Motors, Mechanics, and Power / Re: Supply Current for Relays on: September 07, 2014, 10:08:29 pm
The claim that it needs 15-20 mA "driver current" seems dubious.     That is really too much for a mosfet or opto input.   And too little to drive the relay actuating coil.    It's not clear to me what that is actually refering to.

Try measuring the current that the relay coil actually uses.   Make sure you have a separate power supply for that with enough capacity.
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