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61  Using Arduino / Project Guidance / Re: solar tracker problem on: April 19, 2014, 09:39:02 am
The location of the sun in the sky as a function of time and location on the earth has been well known for a very long time.  Instead of "searching" for the sun Google the equations for location of the sun and apply those to your system.

To do this accurately you will need to know the location of the system, a GPS is more than adequate for that and you will have to go through some trigonometry to do the translation.  Keep in mind all trig functions I have ever seen on a computer use radians as the unit for input and output, you will need to convert degrees to radians and back.  Once again use Google if you do not know the conversions.

Hope this helps.
62  Using Arduino / Sensors / Re: Laser Measurement (SF02) Setup & Library on: April 16, 2014, 10:51:54 am
My first thought was to rotate the laser range finder (LRF) in a plane that id parallel to the ground and make measurements of the range as a function of rotation angle to build a low budget LADAR system.  I looked at the data sheet and the max sample rate was 12 Hz so the system would have to rotate very slowly to get a reasonably good picture from the LADAR.  You would not have to rotate the system through the entire circle if you only need it for guidance because you only need to get a picture of where you are going not where you have been, in this case 12 Hz may be fast enough.
63  Using Arduino / Project Guidance / Re: gaining accurate time on time sensitive measurements. on: April 16, 2014, 10:40:34 am
When you say you need accurate timing does that mean the intervals between your 20 Hz times have to be accurate or are do you mean the absolute time of the measurement (day, hour, min, sec) has to accurate?  These are two different issues and need to be addresses separately.

Address the interval timing issue:
You say you want the error/uncertainty small, you should do the analysis to see how small this has to be first and post this metric.  Maybe a standard external crystal will be accurate enough to meet your needs or maybe you need a temperature compensated oscillator or something more accurate.  Without knowledge of how accurate it has to be you can spend a lot of time and money coming up with a result that is two orders of magnitude better than what you needed.  Possibly using the PPS signal from the GPS to zero the timer as a means of reducing drift would be enough.

The absolute timing issue:
In this case I assume you are concerned about making sure your measurements where the time stamps compare very well with the time stamp on measurements collected from another instrument located in a different location.  This case can be helped dramatically by the PPS signal from the GPS, I have used this when making acoustic measurements over an RF networked group of sensors.

Hope this helps,
64  Community / Gigs and Collaborations / Re: Have a great idea. Need technical expertise and development. on: April 12, 2014, 09:28:09 am
PM Sent

65  Community / Gigs and Collaborations / Re: Co2 Controller on: April 10, 2014, 08:03:52 pm
Nice Sensor
66  Using Arduino / Project Guidance / Re: long range wireless link to arduino on: March 27, 2014, 09:50:01 am
I think a network of XBee 100 mW 900 MhZ transceivers would work for you.  Set up the network of XBee so that each unit sees the unit behind and in front of it.  The XBees will set up the necessary networking if you have the correct setup so it is a pretty easy solution for low data rate data collection systems.

Small solar cells and batteries could be used to power the intermediate transceivers and to conserve power the radios could be turned on once an hour to broadcast the collected data and then go silent.
67  Community / Gigs and Collaborations / Re: Paid project - Peltier driver/controller on: March 26, 2014, 12:01:26 pm

I have worked up a bid, please check your PM's.

68  Community / Gigs and Collaborations / Re: Paid project - Peltier driver/controller on: March 26, 2014, 08:51:53 am

Did you get my PM?

69  Community / Gigs and Collaborations / Re: Paid project - Peltier driver/controller on: March 25, 2014, 03:34:14 pm
Granted LCD screens can not be used for input I assume that Andy meant to display the parameter value in real time as it is adjusted opposed to blindly setting it and waiting for the system to reach its equilibrium to see what effect your adjustment had on the system.  Add a pot or rotary encoder to set the parameters and the LCD to display the value RT and you are good to go.

A temperature delta of +/-0.2° is tight but is simply a matter of selecting the correct sensors and signal conditioning components and gains on the PID algorithm.
70  Using Arduino / Project Guidance / Re: Function to reverse OPERATIONs of another function on: February 26, 2014, 12:44:13 pm
Functions that undo other functions are called inverse functions.  In standard C that are limited to trig function, exponentials and logs pretty much.

Hope this helps,
71  Community / Gigs and Collaborations / Re: geophysics on: January 19, 2014, 09:23:12 pm
The accuracy usually stated in the GOS specs are the horizontal uncertainties, the vertical uncertainties are much higher.  You can get sub-meter vertical accuracy with additional GPS units and some pretty intense processing, but not with a signal GPS receiver.
72  Community / Gigs and Collaborations / Re: Yet another project: a DAQ on: December 17, 2013, 04:39:53 pm
So, I asked him if I were to make an Arduino alternative. He politely answered, "You will find online software for an oscilloscope and the function generator. Maybe a DMM too. But the spectrum analyzer will be harder and we supply some special instruments written in LabVIEW. Be interesting to see how far you get! By the way, we looked at the Arduino choices early on and none of them had the capabilities and performance we needed."

Can we prove him wrong?

I doubt he will be proven wrong unless someone has the resources to assemble a strong team of hardware and software engineers together, especially given the time restraints.  NI has some amazing software for data acquisition, probably not the best available for a dedicated task but the range of what their software does and the ease it does it is amazing.

I spent a lot of time developing data acquisition software development back when a C compiler fit on a 360k floppy disk and the libraries were on another floppy.  I wish labView would have been available and could have spent the time programming doing Physics, buy alas I was a few processors too early.

Not Much Help,
73  Community / Gigs and Collaborations / Re: Arduino Solar Tracker on: December 17, 2013, 10:50:31 am
Why do people use sensors to track the position of the sun when we know where it is and accurate equations have been developed to calculate the position of it. 

I would recommend google to find the equations that will give you the position of the sun in the sky based on your location on the earth and time of day and point you mirror that direction.  Granted this way you will have to do some geometry work on paper, or similar, but once that is done and verified you are done.  I believe this is a safer, and faster method in addition your part count and circuit complexity drops and this is always a great.  Getting the same thing done with a lower part count is my idea of a very good thing.

One cautionary tip is remember that all of the standard trig functions take the angular argument in radians and also return the angular result in radians, so you will need to convert from the degrees you probably use to radians.  Failure to use the correct angular unit in trig functions will cause you a nightmare or two, I started making that mistake about 35 years ago and seem to make it about every 7 years since.
74  Using Arduino / Project Guidance / Re: GPS accurate to microseconds on: November 25, 2013, 11:43:36 am
If the two stations are remote you can use the GPS units to get a time stamp accurate to the accuracy of the system clock as the two recievers will get their pulse per second (PPS) within 10's of nanoseconds.  One way to sync the two units up is to use the PPS line (make sure the GPS unit you are using has a PPS available)  to drive an interrupt on both Arduinos. 

When the PPS interrupt gets triggered you immediately set the system clock to 0 and record the time stamp from the GPS.  Then when you get an interrupt from the zero-crossing detector immediately store the value of the system clock.  When you broadcast the data packet to the central station you send both the time stamp from when the PPS signal was received and the value of the system clock.  It is a good idea to send the timestamp from when the PPS was received in case you missed a PPS signal.

Now think about the "required" microsecond timing accuracy when you are measuring the time difference between 60 Hz signals, I think you are a little overkill.  Whether you need micro or millisecond resolution you still need a way to synch the remote clocks and the PPS from a GPS seems more than adequate for your application.

75  Community / Gigs and Collaborations / Re: Looking for an experienced programmer familiar with Oled displays on: November 12, 2013, 05:53:41 pm
In the past I have programmed quite a few graphic devices but not these, they are interesting enough that I will order 3 to work with and learn the environment given an Adafruit library there should be little problem,

Let me know if you are interested in having me work with you, I have quite a few years of programming experience and do this in my semi-retirement from Lockheed Martin.

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