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1  Using Arduino / Motors, Mechanics, and Power / Re: Delta servo control on: August 31, 2014, 03:39:27 pm
The graph on that web page appears to claim that the servo position is controlled by signal frequency.

That is quite different to the conventional servo interface,   where the servo position is controlled by the duration
of the positive pulse, and the frequency doesn't really matter.

2  Using Arduino / Motors, Mechanics, and Power / Re: Looking for High Torque Servos. on: August 31, 2014, 03:33:32 pm
The base of a robot arm should have a lower torque requirement that the elbow of the robot arm.

The elbow ( and the shoulder ) have to hold up the entire weight of the arm and provide torque to prevent the end of the robot arm falling down.

On the other hand,  at the base of the arm,   the weight of the arm should be carried by some kind of bearing,   and the servo only has to turn it,   not hold it up.
3  Using Arduino / General Electronics / Re: Ohm's Law. on: August 31, 2014, 03:23:08 pm
Furthermore,  if you have a D to A converter which creates an output voltage which increases by x volts for each count on the input,   then your range of output voltages is

0 ,   0+x,   0+2x,   0+3x,  0+4x .....    0+1022x,   0+1023x    

That's it.   1024 different possible output values.

If you adjust your device so that   0+1023x  is equal to 5V,         then x,   which is the step voltage change for each count,   must be 5V/1023

On the other hand,   you could choose to adjust your device so that the maximum possible output voltage is   4.948 V.   If you wanted to.   And then,   you could say that x = 5V/1024

But then,   you could never actually achieve a 5V output,   because to do so would require an input to the D/A converter of 1024,   which is a number than you cannot provide if it is an unsigned 10 bit number.

4  Using Arduino / General Electronics / Re: Ohm's Law. on: August 31, 2014, 03:17:38 pm
I have seen the arguments for both and neither are convincing.
Ask yourself "why do semiconductor manufacturers go to the expense of creating a precision 1.024V reference?"

Does that help?

Not really. No.  It's a hardware issue.   We know that over the range of possible input voltage,   the 1024 possible fixed output levels looks like a staircase if drawn on a graph.    There are several different ways that the graph can be drawn,  sliding it the right and left a little.

Furthermore,   with 1024 output levels,   there are only 1023 vertical steps between them.     If 0 == 0V   and 1023 == 5V,   then the height of each step is  ( 5V - 0V ) / 1023.       

If 0 == 0V   and  1 == 5 mV,     then at what input voltage does the transition from an output count of 0   to an output count of 1  occur ?

at 0.0000001 V ?    at 2.5 mV  ?    at 4.9999 mV ?

and at what input voltage does the transition from 1022   to  1023  ( the highest possible value ) occur  ?

If I draw a diagonal line on my graph which touches each step at the outer edge of each tread,  or the inner edge of each tread,  which of those lines intersects the origin ?

The answers to these questions would show whether a denominator of 1023.  or 1024.  is appropriate.    I don't see how your precision voltage reference is relevant, at all.

5  Using Arduino / Programming Questions / Re: [half-Solved?]simple logic wrong result on: August 31, 2014, 02:56:04 pm
that is exactly the entire code with "counter" in it. The rest of the code has nothing to do with counter.

Which part of the question "What is bb.clicks?"  didn't you understand ?
6  Using Arduino / Programming Questions / Re: Help needed using nRF24L01 for data transfer between two Mega 2560s on: August 31, 2014, 02:46:31 pm
so what actually happens when you try this ?
7  Using Arduino / Programming Questions / Re: 'check' was not declared in this scope issue on: August 31, 2014, 02:37:10 pm
Any help will be greatly

I would suggest a good textbook or online tutorial because at the moment you are floundering around randomly and have no idea what you are doing.
8  Using Arduino / Programming Questions / Re: Help required coding rules comparing received data to float and fixed values on: August 31, 2014, 02:33:11 pm
I don't know the cause or solution.

It is probably because you are not using Windows.

It is even more annoying,  to be a Windows user and to get files which have no line breaks in them at all.

At least you can read the ones you are getting.
9  Using Arduino / General Electronics / Re: Ohm's Law. on: August 30, 2014, 12:56:35 pm
I have my doubts about whether that denominator should be 1023 or 1024,   I have seen the arguments for both and neither are convincing.    It really comes down to a question about exactly how the a/d converter works.

As for the OP's question,     I am assuming that Vin is the 5V  and Vout is the voltage measured by the a/d converter attached at the point between the two resistors.  If R is the unknown resistor,   then

Vout = 5V * ( R / ( R+100) )


Vout/5V  =  R / (R+100)    so    5V/Vout = (R+100)/R =  1 + (100/R)

so  (5V/Vout)-1 = 100/R

so R = 100/((5V/Vout)-1)     which is the same formula as the one in the code which you posted.

Make sure you consider the cases which could result in division by zero.

10  Using Arduino / Programming Questions / Re: for loop like basic? on: August 30, 2014, 12:41:04 pm
Nothing stopping you from writing in BASIC,   if that is really what you want.
11  Using Arduino / Programming Questions / Re: ISO C++ forbids comparison between pointer and integer on: August 29, 2014, 11:16:32 pm
How are you trying to check if an int is equal to a string ?

What are you actually trying to do there ?
12  Using Arduino / Programming Questions / Re: Serial read more than 64 bytes? on: August 29, 2014, 01:49:07 pm
the  code in your first post is wrong.

you copy message[1] into message
you copy message [2] into message [1]
you copy message [8] into message [7]

and then you stick a new char into message [7]

13  Using Arduino / General Electronics / Re: PIR sensors People Vs animals? on: August 29, 2014, 02:24:47 am
Those sensors are not very systematic,   and they are sensitive to both temperature and movement in a way which is not very reliable.

Are you expecting people to be crawling on the floor ?  If not,   then aim the device so that it's region of maximum sensitivity is more than a metre above the floor.

You really need to install the device and then experimentally adjust both the position and sensitivity of the device with a test cat and a test human,   to try to get the discrimination that you want.
14  Using Arduino / Motors, Mechanics, and Power / Re: How to power 4.5v DC motor with 12v power supply using dk electonic motorshield? on: August 28, 2014, 10:55:37 pm
PWM  with a maximum duty cycle of 40%.    Do not waste your time or energy with dropping resistors.
15  Using Arduino / Programming Questions / Re: Help needed with magnetometer coding. on: August 28, 2014, 08:59:00 pm
The reading does constantly change.

If you expect two consecutive readings to be the same,    you will be waiting a long time.
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