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10756  Development / Other Hardware Development / Re: PICOBEE on: April 17, 2011, 08:10:18 pm
Why run the 328 at 12mhz rather then the arduino standard of 16mhz?


10757  Using Arduino / Microcontrollers / Re: ATtiny Programming on: April 17, 2011, 07:54:58 pm
But can I use any of these with the Arduino tiny cores (and the arduino software):

I also have a mac, so people @ sparkfun have had trouble with their clone.


Most hardware AVR programmers (all?) are not standalone devices, they rely on software running on a PC to actually perform the complete programming task. The USBtiny is supported by the popular AVRDUDE software and AVRDUDE does include support for all those AVRtiny chips. However the Arduino IDE does not directly support any AVRtiny chips as distributed. So using a USBtiny programmer, which the Arduino IDE does support via using AVRDUDE internally, does not get you support for AVRtiny chips unless add the needed support files and changes to the IDE to support those type of chips. Some have shown it can be done, but the IDE does not come with that support as standard distribution. One can either use AVRDUDE directly in command line mode on their PC, or modify the arduino IDE to support those AVR chip types.

That make sense?


10758  Using Arduino / Programming Questions / Re: Arduino & thread on: April 17, 2011, 07:44:09 pm
I think for many new to microcontrollers, the idea of threads or concurrency gives the impression of being able to process individual parallel processes and that just does not apply to a single processor arduino board, but rather the terms should be reserved for true multi-core processors. There are several methods to accomplish individual software tasks in a sketch (millis(), interrupts, state machine, etc) but the bottom line for an arduino is that it can only process a single instruction at a time and to handle multiple independent tasks then there is just a whole lot of task switching that will have to be done to emulate true threads or concurrency.

I guess I'm trying to say that for an arduino true threading (or concurrency) can not apply, rather one uses proper program structure to emulate the concept.

10759  Using Arduino / Microcontrollers / Re: ATtiny Programming on: April 17, 2011, 07:27:24 pm
I'm just starting to play around with a couple.  I picked up one of Adafruit's USBtinyISPs and I'm using it with winAVR.

And SparkFun sells a USBtiny clone:

10760  Using Arduino / Installation & Troubleshooting / Re: USB programmer on: April 17, 2011, 07:22:10 pm
I've had very good luck with the Adafruit USBtiny. The IDE supports it directly and it's an easy build.

SparkFun sells a clone version that comes already assembled for less money, but with no case.

The one you linked to has a very nice price, but I would want to hear from someone directly that it works for them within the Arduino IDE.

10761  Using Arduino / Programming Questions / Re: Help setting I2C address on MCP23008 on: April 17, 2011, 04:41:40 pm
From the Arduino reference for the Wire Library:

There are both 7- and 8-bit versions of I2C addresses. 7 bits identify the device, and the eighth bit determines if it's being written to or read from. The Wire library uses 7 bit addresses throughout. If you have a datasheet or sample code that uses 8 bit address, you'll want to drop the low bit (i.e. shift the value one bit to the right), yielding an address between 0 and 127.

10762  Using Arduino / Sensors / Re: Calibrate Temp Sensor on: April 17, 2011, 04:26:12 pm
My question is: How do people "calibrate" the sensors?

Having just looked over the datasheet for this sensor, I don't think the sensor has any internal method of calibrating the device. That would mean you would have to do that independently in your sketch by either adding or subtracting a calibration factor to the reading, and that assumes any sensor error is linear over your required operating range.

 I guess a useful first step is to just run through a temperature range with the sensor using some other temperature sensor as a 'reference' and see what you have. Having worked in industry that dealt with calibrating process sensors I can say with pretty good confidence that words like calibration and accuracy need a lot of operational definitions applied before a successful plan can be applied. 

10763  Using Arduino / Microcontrollers / Re: Schematics of Arduino using ATMEGA8 on: April 17, 2011, 02:28:17 pm
10764  Development / Other Hardware Development / Re: Problems uploading sketches to stripboard arduino using FTDI cable on: April 17, 2011, 10:57:16 am
You have two choices. If your FTDI cable breaks out the DTR signal then you can wire it to the reset pin through a series .1ufd cap and the IDE will automatically reset your chip at the correct time. If your FTDI cable does not provide that function then you must use a manual reset button. The timing is tricky but most use a method of holding down the reset button, then press upload on the IDE and when you see the completed complied sketch size report then release the reset button. May take practice but it will work with a little practice.


10765  Using Arduino / Project Guidance / Re: pin 2 pullup res on: April 17, 2011, 10:50:07 am
If the chip has a fairly recent arduino bootloader installed I believe it already sets the internal pull-up on to prevent the bootloader from responding to noise on pin 2 and hanging the chip up waiting for an upload that is not coming. If the chip does not use a bootloader then there is not concern about noise on pin 2.


10766  Using Arduino / Motors, Mechanics, and Power / Re: Big DC Motor?? 180V dc rated at 12A. on: April 17, 2011, 10:44:55 am
Would I have to go the MOSFET route or could I simply get away with using an appropriately rated SSR, triggered by the PWM output of the Arduino to "chop up" a 180V DC source?

Most SSR are for AC voltage only as they use SCRs or Triacs that won't work with DC voltage switching.

Going with logic level mosfets (if you can find some rated for such high voltage) would be the simplist method and then the arduino could use a PWM output pin to vary the speed of the motor using analogWrite() statements.

The 180v DC would be coming from a simple transformed mains - rectified and smoothed.

Be sure your AC outlet, circuit branch wiring and panel circuit breaker is rated for this current.

10767  Using Arduino / Sensors / Re: PH Sensor on: April 16, 2011, 06:23:29 pm
Here is an E-bay seller that has both interfacing modules and PH probes. Don't underestimate the exacting requirements of the input electronics needed to accurately read PH probes. It's a difficult measurement with a large dynamic range.

10768  Using Arduino / General Electronics / Re: Does an OUTPUT require a Pull Down resistor ? on: April 16, 2011, 06:07:59 pm
Thank you floresta. I'm sorry for my attitude. After some searching, I realized tri-stated means the same as High-Z but still it's the property of the gate. The pull-up resistor seems to me to be "not a part of the tri-state gate". P77 is the diagram of a pin. I'll study it more.

"Tri-state" defines a possible enabled state of a digital output pin, not an input pin. Some output types are open collector, open drain, TTL output and TTL Tri-state. Each is electrically different. The output pins on an arduino are not strictly defined as Tri-state output pins as there is no way to have the pin enabled as an output pin and still be in a tri-state mode. Once you use the mode statement to set a pin to output, it will immediately assume either a active high or active low state. Only by redefining the pin as an input pin with the mode statement will the pin assume a Hi-Z mode, assuming the internal pull-up is not enabled. An Arduino I/O pin can be made to mimic a tri-state output but only by changing it's mode from output to input and then back to output depending on what state you need it to be placed in. This is seem in the popular Charlieplexing scanning technique.


10769  Using Arduino / Interfacing w/ Software on the Computer / Re: Use serial monitor while COM port is in use? on: April 16, 2011, 04:27:26 pm
For debugging purposes, how can I use the serial monitor for debugging while the COM port is in use by Simulink? I get an "in use" error from either Simulink or Arduino, depending on which application starts first.

This is a restriction from the PC operating system, only allowing one application at a time to connect to a specific comm port.

Also, How can I use () to interpret a 16 bit signed integer being sent by the PC?

The Arduino function can only deal (read) with one byte per read statement. If sending multbyte variables from a PC then your sketch code must read them as a series of individual bytes and then reassemble them into a int or long or float or array variable, as the case my be.

10770  Using Arduino / Sensors / Re: Calibrate Temp Sensor on: April 16, 2011, 02:10:36 pm
I am building a controller for a salt water reef aquarium that will turn on and off heaters, lights, fans, etc. based on the temperature of the water.  I'm using DS18B20 sensors and I have three of them.   In bench testing all three of them vary by up to 1 degree.  In addition they all show higher than my standard thermometer on the wall although I can't really vouch for it.

My question is: How do people "calibrate" the sensors?  I can vary the output in code to agree with the wall thermometer.  In practical use the temp should only vary by 3 or 4 degrees.  Is there a practical "known accurate" thermometer to be used for calibration?

One method is to use 'known' temperature sources to validate/calibrate temp sensors. Boiling water (100C or 212F) and crushed ice baths (0c and 32f) are pretty easy standards to calibrate with, if your sensor is rated to the two temp values.

 Other then that it's a "Man with one watch always knows the time, man with two watches never quite sure" situation.  smiley-grin


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