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31  Using Arduino / General Electronics / Re: charging Li ion battery on: May 18, 2014, 02:31:45 am
""Question. If I only want to do the constant current charge till 4.0v what must I limit my voltage to? I'm slightly confused because a constant current adjusts the voltage to keep a constant current. Will this not cause the charging voltage to go above 4.2volts?""

You have already answered your own question.  You raise voltage to keep a constant current but once you reach 4.2 you revert to constant voltage  -  hence voltage never exceeds 4.2v
32  Using Arduino / General Electronics / Re: 5:1 AC Step Down Transformer on: May 12, 2014, 02:50:49 am
You specified a frequency of 134.5kHz.  If that is correct then it is unlikely that an iron cored transformer will meet your needs.  You will probably need a ferrite core unit and at those sort of frequencies you should be able to wind your own using shellac coated (or equivalent) copper wire.  Or alternatively buy something like one of these http://uk.rs-online.com/web/p/telecom-transformers/0196369/.  From its data sheet you'll see it offers high frequency bandwidth and high voltage isolation.  Whilst its ratio is 1:1 rather than the 5:1 you desire, you can use a simple resistor divider on the output stage to get your desired ratio.
33  Using Arduino / General Electronics / Re: Is this calculation correct ? on: May 11, 2014, 08:24:43 am
Even if you cannot draw a proper schematic, draw an illustration of what you want to do.  If you do not have a drawing package, sketch it on paper then take a GOOD quality photograph and post that
34  Using Arduino / General Electronics / Re: Is this calculation correct ? on: May 10, 2014, 05:51:55 pm
If I understand correctly, you want to discriminate up to 39 values in a chain resistor.  Can you present a diagram of how you intend to connect these via a switch system to the single arduino input.  Also where is the calculation that you want verified. Might I suggest you google  R/2R resistor chain.
35  Using Arduino / Motors, Mechanics, and Power / Re: Gearmotor program on: May 08, 2014, 05:14:21 pm
Write your programme to do the following
a) Manually input set points for temperature and humidity
b) Measure temperature and humidity (measured variables)
c) If measured variables equal set-point then motor drive = zero
d) If measured variables exceed set point then drive motor clockwise
e) If measured variables are lower than set point then drive motor anti-clockwise

You can add a further function in that the motor speed is set as a function of the error between setpoint and measured variables.  This can be achieved by using a PWM output.

Edit : And once you have that up and running you can also introduce Integral and derivative functions so you end up with a fully operational PID controller.

As others have said you will need an H-drive

Be aware that you cannot drive a DC motor to a known position unless it has some form of position sensor fitted.  If you do require predetermined positions you need to use a servo motor.
36  Using Arduino / Motors, Mechanics, and Power / Re: 12v DC pump/ SSR relay on: May 07, 2014, 07:52:16 am
Model number of your SSR would help greatly in understanding what you are attempting.  What is the purpose of the relay board. 
If it's a simple DC pump you are controlling then a FET would probably be a better, and cheaper, choice.   
Plus, that's not a circuit - it's a collection of inter-connected components.  A circuit diagram should graphically (ie drawn) show how each component is electrically connected to others.  Proprietary devices, such as the arduino, can be shown as simple boxes, with i/o, power and control points clearly identified
Then we may be able to assist.
37  Using Arduino / General Electronics / Re: Can i used Arduino uno in indusry? on: May 07, 2014, 02:47:20 am
Some (many) years ago I looked at a relatively inexpensive industrial "safety system" PLC that was based on three bog standard processor chips, each of a different manufacturer.  Each processor had its own specific programme and OS code running and the results of all three processors were then read by a 2-out-of-3 logic array.  Unless at least 2 of the individual processors and their associated code produced identical outputs, the system was deemed to have "failed" and the process shut-down.  Because of both diversity and integrity of the processing and computation the system was "fail-safe" and had the necessary approvals.
38  Using Arduino / General Electronics / Re: Can i used Arduino uno in indusry? on: May 06, 2014, 09:39:54 am
Speak to your company's insurance underwriter for an official answer, because at the end of the day, it'll be their lawyers who decide whether or not you exercised due diligence.

Provide the device does not form part of any system that might expose employees of buildings to undue risk then it should be OK.

If being used in a "Safety System" then forget about it.
39  Using Arduino / General Electronics / Re: 0ohm resistor, why? on: May 06, 2014, 02:40:56 am
and the only situation where, if both resistors are 0R0, two resistors in series is the same as two resistors in parallel ie  R1 + R2 = R1 x R2 / (R1 + R2) which equates to R12 + (2 x R1 x R2) + R22 = R1 + R2

Wot a load of rot  smiley-grin smiley-grin smiley-grin
40  Using Arduino / General Electronics / Re: How to change the range from 2 to 25 or above? on: May 03, 2014, 10:27:27 am
With all due respects, if you don't know what's involved in increasing a transmitter's range then you have absolutely no chance of building a working FM transmitter. 
Such work requires a good understanding of electronics and how components which aren't even connected to each other can influence device operation simply because of their physical proximity to each other.
If you really do want a high power FM transmitter then your only chance of success is to go out and buy one.  If the law of your country prohibits this then so be it.
41  Using Arduino / General Electronics / Re: Heating Problem: Powering Arduino Mega 2560 with 5V - 10A Transformer on: April 30, 2014, 02:39:12 pm
And you also need to confirm, by means of a test meter, that the output of your power supply is indeed 5 volts DC.
42  Using Arduino / General Electronics / Re: Heating Problem: Powering Arduino Mega 2560 with 5V - 10A Transformer on: April 30, 2014, 01:17:33 pm
What is over-heating, the transformer or the arduino

I take it your "transformer" provides a smoothed DC output  and not AC as a transformer does.

6 x 10*-3 x 100 = 0.6A not 6A as you show.

Can you supply a diagram of how you have connected things up.
43  Using Arduino / General Electronics / Re: Resistors in a circuit on: April 29, 2014, 03:34:43 am
IF you can guarantee that ONLY one LED at a time will be illuminated then you can indeed use a single resistor.  However if there is ANY possibility of more than one LED being illuminated simultaneously then you need individual resistors.
44  Using Arduino / General Electronics / Re: Quick resistor question on: April 27, 2014, 04:18:18 am
Having read what CR suggests I agree, you can indeed use a single resistor.  Since each LED will have a dedicated output pin on the arduino the single resistor will act as the common current control device.  By using controlled switch-on you ensure that only one LED output at a time is actually active.  I'd surmise a frequency of around 25Hz shouldn't be noticeable.  To overcome brightness variation concerns you could drive each output via PWM rather than simple ON-OFF and effectively control the brightness between different LED colours.  Since the PWM frequency will be much higher than the multiplexing frequency there shouldn't be any problem combining both switching frequencies.
45  Using Arduino / General Electronics / Re: Quick resistor question on: April 26, 2014, 01:52:56 pm
If your design is a true traffic light simulation there is a condition where you will have two LEDs on each column lit simultaneously.  In the UK this is Red + Amber.  The full sequence being Green -- Amber -- Red -- Red+Amber -- Green.  The sequence may be different in other systems.   I presume at the moment you have a current control resistor attached to each LED.  IF, and it's a big if, a sequence group of 3 LEDs were controlled and lit singley then you could use one resistor to drive each LED in this group of 3.  Each group of 3 would require their own current control resistor.    Because you may have 2 LEDs operating together you cannot use a single resistor because the current demand of the 2 in parallel is obviously greater than the individual LEDs.  Say each LED has a specific current demand (say 20ma) the current limiting resistor is sized to suit this current, generally somewhere around 180ohms.  Two LEDs lit together will require 40mA or so and the voltage drop across a 180ohm resistor would exceed the output voltage of your arduino, or to put it another way the drive current through each LED would be approximately half of what it should be and the LEDs would be dimmed.
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