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16  Using Arduino / General Electronics / Re: Power Supply questions on: July 22, 2014, 11:37:19 am
I have a couple questions regarding it: the power supply has a +V and -V as well as ground. does it matter what V i use?

I think it's just weird labeling and "V-" really means "GND".
Looking at the spec sheet:
-V is the negative terminal of the 12V supply,
+V is the positive terminal of the 12V supply.
PE is the protective earth connection.
There is no "ground" connection, you are free to choose ground.

Note that this is an isolated supply, but the output terminals mustn't go too far from
earth (the input-output isolation is tested to 3kV, but output-earth isolation is only
tested to 500V)

The leakage current is under 1mA, which means the outputs could be floating
at mains voltage levels if not tied to PE somewhere - recommended unless you have
a genuine reason not to.
The first thing you should do when it arrives is probe it with a multimeter.
Definitely - your multimeter is invaluable all the time, check everything
you can and fewer expensive mistakes will happen.  In particular you can
verify voltage and polarity.
17  Using Arduino / Programming Questions / Re: Significant difference between millis() and micros() on: July 22, 2014, 11:26:20 am
Do you concede that the issue is how long the code takes to convert
strings to bit-patterns on the LCD, not any difference in behaviour of
micros() and millis() which both work as expected.

You must compare apples to apples, not apples to oranges, to compare
the two functions, conflating the code being timed with the code printing
out the results of the timing has been the confusion and you are still doing it.
18  Using Arduino / Programming Questions / Re: How can do something like this: IF HIGH && > 3000ms on: July 22, 2014, 11:21:57 am
If you want time to enter the equation, you need it to literally
enter the equation...

const int xbeePin20 = 7;       // pin 7
int led = 12;

void setup() {
  Serial.begin(9600);                // For testing
   pinMode(xbeePin20, INPUT);         

unsigned long went_high = 0L ;
boolean pin20_oldstate = false ;

void loop()
  boolean value20 = digitalRead(xbeePin20); // Pin 7
  if (value20 != pin20_oldstate) // detect changes
    if (value20)
      went_high = millis () ; // capture rising edge timestamp
    pin20_oldstate = value20 ;

  if (digitalRead (xbeePin20) && millis () - went_high > 3000)
    digitalWrite(led, HIGH); // LED 12
    digitalWrite (led, LOW) ; // must turn it off too
So you need a variable to record timestamp, and then compare current time
to that timestamp if appropriate.

Note the idiom of detecting a pin state change - use a boolean variable to record
the previous state.  Then the timestamp only gets set when the pin transitions HIGH.

The actual test turning on the LED will repeatedly fire, but that's OK because
repeatedly turning an LED on isn't a problem.  I've added code to turn it off too,
that's probably needed somewhere!
19  Using Arduino / Motors, Mechanics, and Power / Re: DC Motor with External Power on: July 22, 2014, 11:10:45 am
A small 9V battery is useless for powering motors.  You need battery pack that can provide
enough current (several amps peak will be expected).  This means good quality branded
AA rechargables or alkaline, LiPo or SLA.

PP3 9V battery - perhaps 100mA
AA cell, cheap - perhaps 500mA
AA cell, quality - 1A to 2A
LiPo/SLA - 10A+, fuse required.
20  Using Arduino / Motors, Mechanics, and Power / Re: How to Control a Motor that has Been Taken Out of a RC Car with the Arduino on: July 22, 2014, 11:00:53 am
But first you need to find out how much current the motor takes - motor
drivers like the L293 and L298 have very limited current capability.

Some more information about the car and or motor?  Measure the motor
21  Using Arduino / Motors, Mechanics, and Power / Re: Use computer PSU for high-amperage LED RGBW on: July 22, 2014, 10:58:55 am
More to the point you expect us to answer questions about an unknown
power supply - can you not at least say what it is?
22  Using Arduino / Motors, Mechanics, and Power / Re: Minimizing power consumption of an Uno? on: July 22, 2014, 10:53:49 am
The USB->serial converter chip is also taking current, if you want micro-power
behaviour the Uno is the wrong board.  A bare-bones board or similar is needed.
23  Using Arduino / Motors, Mechanics, and Power / Re: I want to stop a stepper motor with Arduino Motor Shield on: July 22, 2014, 10:52:04 am
AccelStepper library perhaps?
24  Using Arduino / Motors, Mechanics, and Power / Re: Arduino Motor Shield Help on: July 22, 2014, 10:49:42 am
Because that is a large low-impedance bipolar stepper motor taking 2.5A rms (3.5A
peak) requiring a constant-current chopper-drive controller to perform at speed.

Typically such a controller would run at 36 -- 80V supply to overcome back-EMF and
permit fast current-switching.

Such motors are not designed for constant-voltage drive at all.
25  Using Arduino / Motors, Mechanics, and Power / Re: Mystery 30A ESC programming. on: July 22, 2014, 06:15:28 am
Hello everybody, I need a little help with this mystery ESC. (
From what i've seen on the web, for it to work you have to first calibrate and program it. Problem is, I've never used one of theese, so I'm a little clueless on how to proceed. I've got no access to a RC transmitter/receiver or whatsoever, just my arduino mega.
No, ESCs work out of the box - but you can reprogram the throttle response
curves and things if you want.  The Servo library on the Arduino can generate
control signals for ESCs and servos.

What I want to do is controll a brushless motor's speed AND direction through a pin in the arduino.
Most brushless ESCs don't go backwards as they are for aircraft and helicopters, and
sensorless BLDCs don't have closed-loop control at low speed.
26  Using Arduino / Motors, Mechanics, and Power / Re: Does this MOSFET implementation look correct? on: July 22, 2014, 06:11:14 am
The schematic is unreadable as its been shrunk too much.
27  Using Arduino / Motors, Mechanics, and Power / Re: I want to stop a stepper motor with Arduino Motor Shield on: July 22, 2014, 06:09:14 am
You've got the wrong controller for that motor, it needs a constant-current chopper
drive capable of 3.5A output really.  The L298 can't deliver the current needed and
that motor will only go very slowly driven from an H-bridge.  The windings are
probably something like 0.5 to 1 ohm, so you'll be wasting most of your power in
the L298 darlington stages...

Low impedance stepper motors need current-control drive, high impedance motors
can be voltage driven.
28  Using Arduino / General Electronics / Re: Which transistor to control 12V (350mA) Solenoid Valve? on: July 22, 2014, 05:55:19 am
Definitely use a 220 ohm base resistor, 1k is rather too large - see my analysis above
for why.
29  Using Arduino / General Electronics / Re: TRIAC AC switch , need some info on: July 22, 2014, 05:51:42 am
R5 & R7 seem to be very low. They will draw 7.5A and dissipate 1.8 Kw.
To top that they do not do anything.
on forum i read that they are needed (R and C at the end) if load is inductive

That's a snubber network, but you drew two resistors, which is completely different
circuit.  Yes snubber networks are needed for AC inductive switching (be it a triac or a relay
or even just a mechanical switch).
30  Using Arduino / Motors, Mechanics, and Power / Re: Use computer PSU for high-amperage LED RGBW on: July 21, 2014, 05:28:44 pm
Computer PSUs have a current rating for each separate voltage, you have to avoid
exceeding any of them individually.
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