Show Posts
Pages: 1 ... 1006 1007 [1008] 1009 1010 ... 1169
15106  Forum 2005-2010 (read only) / Interfacing / Re: vacuum/boost sensor on: April 14, 2009, 04:38:36 pm
Look up the difference between gauge pressure and absolute pressure sensors.

You have a gauge pressure device that compares a sensing pressure line to your local barometric pressure. A absolute pressure gauge has a sealed evacuated lead so that the sensing line is measuring the absolute pressure relative to the vacuum sealed lead.

Lefty

15107  Forum 2005-2010 (read only) / Interfacing / Re: Arduino Mega: Sensor Range Help on: May 14, 2010, 06:02:03 pm
Yes, you should test the analog inputs pins independently from your sensor and sensor wiring. That can be as simple as jumpering +5vdc to your analog input pin 1 and connecting ground to analog input pin 2 and then run your posted program.
 The results of that test will tell you which direction you need to go next. Will take 1 min to test and then give us the results. If the results of the test are good then you will have to somehow provide us with wiring details and sensor information to help any further. If the test results are bad then trying a different mega board with the same test would be called for.

Lefty
15108  Forum 2005-2010 (read only) / Interfacing / Re: Fast speed encoder counting fail !!! on: August 23, 2009, 07:01:00 pm
The number of statements and statement types in your ISR routine will normally be the limiting factor in how fast you can keep up with encoder generated interrupts. Perhaps if you could post your sketch there might be some improvements that can be made.

One simple speed up one can take is to use direct port access when reading I/O pins inside the IRS Vs doing DigitalRead statements.

Lefty



15109  Forum 2005-2010 (read only) / Interfacing / Re: Lots of flashing LEDs: constant current ICs? on: May 10, 2010, 07:21:41 pm
I used the following in my 5x5x5 led cube project. 16 bit constant current serial in and you can daisy chain as many in series as you require. One resistor sets the constant current value for the 16 drivers. Avalible in DIP package, I got mine from Newark Electronics.

http://www.allegromicro.com/en/Products/Part_Numbers/6276/index.asp

Lefty
15110  Forum 2005-2010 (read only) / Interfacing / Re: POWER PINS on: May 13, 2010, 11:09:38 am
Quote
3V is an output from the USB / Serial chip. There is nothing out of this if you use external power.

GM: Are you sure about that statement. The USB FTDI chip is still powered even if you are on external power, therefore it's internal 3.3vdc regulator output should still be active and available, no?

Lefty
15111  Forum 2005-2010 (read only) / Interfacing / Re: TX3 on Mega board? on: May 13, 2010, 03:21:14 am
 am asking myself why there are TX1-> TX3 and RX1-RX3 on the MEGA board. I thought I can generate software serial ports as many I want to.

Software serial ports and hardware serial ports are two different things. The mega 1280 chip has four internal hardware serial ports. The mega 168/328 has one internal hardware serial port.
If TX3/ RX3 is a dedicated RX/TX how can I access it?

All explained in the Arduino reference documentation:
http://arduino.cc/en/Reference/Serial
 
Lefty
15112  Forum 2005-2010 (read only) / Interfacing / Re: Arduino Nano + external battery on: May 04, 2010, 02:06:46 pm
yes, you can wire 9vdc battery to the Vin pin. You won't get long life for such a battery as they have a pretty low mah rating and are among the most expensive batteries to use Vs the mah provided.


Lefty
15113  Forum 2005-2010 (read only) / Interfacing / Re: PWM Through an AND Gate? on: May 11, 2010, 03:19:19 am
Typical limit switches for motors are often a safety item and it is best that they cut the source voltage to the H-drive directly rather then limit via logic level control. Of course in that case the limit switches would have to have current rating equal or higher then the max motor current drawn.

Just throwing out the idea.

Lefty

15114  Forum 2005-2010 (read only) / Interfacing / Re: Pin 13 w/ led using with pushbutton. on: May 09, 2010, 02:25:07 pm
Quote
pinMode(pin13, OUTPUT); or pinMode(pin13, INPUT); so since the LED is an output and the pushbutton is an input you can't connect both of them to it.

Not exactly. You can program pin 13 to be a input pin, however the signal that will drive it will have to be able to source the led current (when the signal is HIGH) which with it's 1k ohm resistor will be around or under 4ma. I think you would also need to enable the internal pull-up resistor to prevent the pin from floating if you are using a simple switch wired to +5vdc, or use a external 10k pull-down resistor as the led will not be biased on when the pin is a input and might float as I said.

Lefty

15115  Forum 2005-2010 (read only) / Interfacing / Re: High-speed, up/down counter on: May 08, 2010, 08:54:58 pm
Well the Arduino mega does allow for five user interrupt pins I believe, so three of them could service the channel A of each of the three encoders. There would need to be 3 input pins assigned for the three channel B signals from the encoder. From there each of the three ISR functions could maintain an up/down counter just as shown in some of the encoder libraries.

 So the question is, are three asynchronous 17khz interrupts too fast to prevent missing steps? The ISR needs to be written 'lean and mean', but my gut says I think it can be handled. Keep in mind that the ISR triggers have the option on when the interrupt is generated, change, low, etc. So perhaps some playing with the trigger type can help prevent missing steps for a tradeoff of a small amount of timing skew.

Lefty
15116  Forum 2005-2010 (read only) / Interfacing / Re: How to make UART Tx idle state logic LOW on: May 07, 2010, 11:55:26 am
Quote
Would I have to disable the internal pullup and use an external pulldown?  Any ideas or suggestions would be appreciated.  Thanks.

Interesting problem.

Not sure the Arduino serial library uses the internal pullup or not on pin 0. If you are using a standard Arduino USB with a FTDI USB serial converter chip then the solution if possible is a little more complex.

 The HIGH (serial idle condition) on the serial rec pin 0 is coming from the TTL serial output of the FTDI chip through a series 1k resistor. The only way to overcome this I think would be to change pin 0 to an output pin and set it LOW. You would have to then change it back to a input before you did any serial commands.

Lefty
15117  Forum 2005-2010 (read only) / Interfacing / Re: 7.2V Motor - 10Amp - How to power and to control on: May 09, 2010, 09:09:55 am
Quote
What size resistor, if any would be required between the arduino pin and the Mosfet gate?

None is required. However you may wish to have a 10k ohm resistor wired from the gate to the source pins of the mosfet. This will ensure the mosfet turns off if the arduino is ever powered off but the motor still has battery voltage applied.

Lefty
15118  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
Quote
So this guy should be usable?

Yep, good choice.

Lefty
15119  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
Quote
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
15120  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
Pages: 1 ... 1006 1007 [1008] 1009 1010 ... 1169