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15106  Forum 2005-2010 (read only) / Interfacing / Re: 7.2V Motor - 10Amp - How to power and to control on: May 03, 2010, 12:52:45 pm
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So this guy should be usable?

Yep, good choice.

Lefty
15107  Forum 2005-2010 (read only) / Interfacing / Re: 7.2V Motor - 10Amp - How to power and to control on: April 18, 2010, 11:15:44 am
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and gate threshold of <= 3V, sorted by price

The gate threshold spec is not the spec to go by. One really has to look at the graphs showing source/drain current flow Vs gate voltage when the gate is at the 4.5-5vdc that an Arduino can supply. True logic level MOSFETS will have a gate threshold voltage as low as 1.5vdc or so. Gate threshold spec is the gate voltage where the mosfet just starts to conduct, and not it's fully saturated gate voltage.

Lefty
15108  Forum 2005-2010 (read only) / Interfacing / Re: 7.2V Motor - 10Amp - How to power and to control on: April 17, 2010, 01:33:33 pm
The IRF520 is NOT a logic level MOSFET, an Arduino output pin cannot fully turn it on without additional external components. That's why I stated using a LOGIC LEVEL N-channel mosfet is easier to interface with an Arduino.

OK being in EU. Transformers are sometimes much cheaper if you can find surplus dealers, rather then full retail new stock.

Lefty
15109  Forum 2005-2010 (read only) / Interfacing / Re: 7.2V Motor - 10Amp - How to power and to control on: April 17, 2010, 01:21:20 pm
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Lead-acid cells?
Half-a-dozen should be bang-on 7.2V.

Hows that? Six lead-acid cells (2.1v each) makes up a 12.6V battery, just like in cars.

Lefty
15110  Forum 2005-2010 (read only) / Interfacing / Re: 7.2V Motor - 10Amp - How to power and to control on: April 17, 2010, 01:14:09 pm
Well the motor stall current rating is a worst case condition for a motor, called locked rotor, and shouldn't be a normal situation. Your motors might only draw half that in most normal cases, but it really depends on the mechanical demand placed on the motors. You could use a transformer with a lower current capacity and fuse it at the transformers max current rating.

 The fact you are considering an AC transformer says you don't need portability from AC mains. Batteries (Li-po 2 cell) would have no problem handling 10 amp loads depending on the mah rating of the cells, however their costs plus charging equipment will exceed the cost of a AC transformer/rectifier/filter. So unless you require portability your first plan is more economical.

A N-channel MOSFET is the best switch device for this kind of application. However it's made easier if you use a logic level N-channel MOSFET as the Arduino can only supply +5vdc as a turn on voltage and a normal MOSFET requires 10vdc to fully turn on. Also the MOSFET should be rated at several times the worst case current draw, so 25+ amp ratings would not be overkill.

Here is an example of a nice logic level high current mosfet:

http://www.goldmine-elec-products.com/prodinfo.asp?number=A20225

Here is a transformer that should work worst case:

http://www.allelectronics.com/make-a-store/item/TX-6310/6.3VCT-10A-POWER-TRANSFORMER/1.html

Lefty
15111  Forum 2005-2010 (read only) / Interfacing / Re: Getting 12V OUT of an Ardunio on: May 08, 2010, 11:41:00 pm
An Arduino does not create power, it consumes power. You can power an Arduino with 12vdc by applying it to the external power connector on the board. To control an external device at 12vdc like a door strike, with require a 5vdc coil relay or a transistor so that the internal +5vdc microcontroller can control the power on/off to the 12vdc device. It would much simpler if you had a 12vdc power source so you could power both the Aduino board and your door strike from the same source. Converting 9vdc to 12vdc is possible but somewhat expensive compaired to just using a 12vdc power supply in the first place.

 There are pleanty of examples in the Arduino web site on how to power an Arduino and how an Arduino can control external devices at all voltages. Check them out.

Lefty
15112  Forum 2005-2010 (read only) / Interfacing / Re: Arduino control Full state space Ball and Beam on: May 03, 2010, 11:15:24 pm
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So can u plz help me out in the C code for this??

So what form of help are you looking for:

1. Write the program for you?
2. Show you how to start learning programming?
3. ?

Lefty
15113  Forum 2005-2010 (read only) / Interfacing / Re: Oxygen Sensor Question on: May 05, 2010, 01:45:50 pm
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So Mark and Lefty can one of you explain this to me like I'm a 4 year old.

 Not sure a normal 4 year old would be a good subject to explain all this.  ;D

Anyway if you change to the 1.1 volt internal reference (and do the 'dummy read' to allow the mux to settle) then you have a input scale that reads a 0-1.1vdc as a 0-1023 integer. You would could then utilize the mapping function to scale this integer to the actual measurement range you are using: X= map(rawadreading,0,1023, 0, 1100); This would result in a variable X that is reading the actual millivolts value of the input signal. That should result in the near best A/D resolution that the 10bits A/D can have.

That help?

Lefty




http://arduino.cc/en/Reference/Map
15114  Forum 2005-2010 (read only) / Interfacing / Re: Oxygen Sensor Question on: May 05, 2010, 12:20:00 pm
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I think the available reference settings are either Vdd or Vref pins or the internal 1.2V reference.  IIRC an ADC conversion takes 13 ADC clocks and the ADC clock is set to about 150kHz.

I think I read the Mega board (mega1280 chip) also has an additonal internal 2.56 volt reference, but it's not yet supported by the Arduino core software. I think it might be a addition that might be added someday to the core.

Lefty
15115  Forum 2005-2010 (read only) / Interfacing / Re: Oxygen Sensor Question on: May 03, 2010, 03:26:51 pm
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So unless I can limit that to one pin i don't think that would be an option.

Well to a degree you can. Software commands can change the A/D reference used on the run before reading each channel. ( http://arduino.cc/en/Reference/AnalogReference ) Using external op amps is also viable but there is no single op-amp device or circuit that covers all cases. perhaps a list of analog voltage ranges you wish to cover would be helpful.

 If you are going to have extensive A/D requirements then perhaps you should look into using external A/D converter/multiplexers. Some of these have build in programmable gain stages and many offer more the 10 bits of resolution. The built in Arduino A/D pins are very useful and easy to use, but they are not close to current state of the arts in instrumentation A/D capabilities. The +/- 2 bits of accuracy specification should be looked at closely to see that it will meet the expectations of your application.

Lefty

15116  Forum 2005-2010 (read only) / Interfacing / Re: Powering Arduino with 5V regulated supply on: May 05, 2010, 06:35:42 pm
To power a Arduino board with an external regulated +5vdc, I like to take a old USB cable and hack off the PC end, locate the + & - leads and power the board through the on board USB connector. That way the auto-voltage circuit still functions as designed and you get to utilize the on-board USB thermofuse.

Lefty
15117  Forum 2005-2010 (read only) / Interfacing / Re: selecting a waterpump to use with arduino on: May 04, 2010, 06:10:43 pm
Maybe a junk yard car windshield washer pump would do the job cheap. They should be 12vdc and you could use a relay or logic level mosfet transistor to turn the pump on and off under program control.

Lefty

15118  Forum 2005-2010 (read only) / Interfacing / Re: How could I detect this? on: January 09, 2009, 07:14:03 pm
Well looking at a data sheet via google it seems that the flame current used to detect a valid flame is in the microamp range. This means that a lot of amplification would be required to interface with the Arduino. Without internal schematic of the flame detector circuit it would hard to give more more details. Did you anticipate just sticking a new probe into the flame and using independent drive and sensing circuits to detect the flame independently from the existing equipment?
I suspect using independent IR photodetectors mounted in sight tubes to each burner would be much more straight forward.

Lefty
15119  Forum 2005-2010 (read only) / Interfacing / Re: How could I detect this? on: January 09, 2009, 05:52:54 pm
Flame management is a very safety sensitive application. At the refinery I worked at all the control components and equipment used had to meet certain industry fire and safety certifications and that sometimes prevented us from using more general and up to date components and equipment that didn't carry such certifications.

That being the case it's really questionable to give advice and suggestions for 'homebrew' type installations. Home and commercial insurance policies can also be effected. YMMV, but think carefully about this before actually implementing.

Lefty
15120  Forum 2005-2010 (read only) / Interfacing / Re: How do I make a resistive touch switch? on: May 02, 2010, 04:59:36 pm
DVM complexity and cost is mostly due to the number of 'counts' it's internal A/D converter has, not it's number of display characters (display characters are cheap). The most common A/D for DVMs is a 2000 count converter (0-1999). So 'filling in that first character position to a full 9 could require a 10,000 count A/D converter, resulting in a much higher cost instrument.

Lefty

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