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121  Using Arduino / Project Guidance / Re: incorporating GPS in a pan/tilt mount on: October 03, 2012, 08:14:39 pm
The BMP085 you specc'ed has typical error of +/-1hPa which corresponds to almost +/-10 meters of difference in density altitude.   How does the error in density altitude affect your system, the error causes your system to have an error of +/- 10 m so when the calculations are made to calculate the pointing direction of the pan tilt system.  There will also be error in Lat and Lon from the GPS uncertainty so this will cause an error in the pan tilt calculations.

Are these errors too large?  Whether the error will cause problems for you is dependent upon the distance to the objects of interest and the field of view of your camera, to name a few.

122  Using Arduino / Project Guidance / Re: Weather Station / Data Logger on: October 03, 2012, 09:29:18 am
A note on using 2-3 decimal points as an accuracy metric or for that matter any figure of merit.  Assume I make a measurement of a 1.0 centimeter this is 0.00010 kilometers.  The first result has one decimal place and the second has 5, is the measurement any different by only changing the coordinate system?

You need to be a little more quantitative when making requirements on accuracy.

In my research on weather sensors it seems the humidity is hard to measure to within say +/-3% without spending a lot of money and doing occasional instrument calibration.  Buying the equipment for calibration will drive the cost up very quickly.

When starting out on a design of a sensor system making it very accurate is always the initial response.  Somewhere along the design process you need to ask yourself what it is you need to accomplish with the instrument and let that drive your accuracy requirements.  In my first reply I talked about using a humidity sensor that was accurate to +/-5% and saying that was good enough for my application, density altitude measurement.  Humidity's influence on the density is very small so I could get away with a lower quality measurement of it, ther +/-5% error on the humidity did not map over to a +/-5% on the density altitude.

On to sensors, for measuring pressure Freescale was a great line of MEMs sensor and I would encourage you to look at their website.  MEMs sensors was dramatically driven the cost and size of the sensors down and you probably want to exploit that.

123  Using Arduino / Project Guidance / Re: Weather Station / Data Logger on: October 02, 2012, 10:35:28 pm
I have some boards at the fab shop for what I call my Weather Board, it will report air pressure, temperature and rel humidity on I2C.  The overall size of the board is just over a square inch.

Keeping the price of the board down I made some choices of the sensors that may or may not meet your "very accurate" threshold.  The accuracy thresholds may be a problem for relative humidity as the main need for the board was to measure the density altitude and humidity is least significant of the 3 measurements.  You might want to tell us what "very accurate" means so then myself and others know if what have is good enough to help you out.

Being I2C for all the sensors it can easily be used with an Arduino and implemented with GPRS shield.
124  Using Arduino / Microcontrollers / Re: standalone programmer on: October 02, 2012, 08:54:41 am
I use Atmel's AVRISP MkII, it will everything you ask and works well with AVRDude so all you would have to do is write a short batch file and the users could very easily do what you need.  If you need a GUI to do the tasks you could download AVR Studio, Atmel's free IDE.

Here is a link to the MkII

125  Using Arduino / Sensors / Re: The proper way to integrate the MCP9700 temp sensor into an arduino on: September 29, 2012, 06:15:59 pm
Are you using the USB cable to power the Arduino and then the Arduino to power the sensor, if so that may be your problem as the voltage out of the USB can be noisy.  Try using a different method of powering your Arduino like a wallwart DC source of say 9 volts plugged into the DC socket on the board, this may solve your problem.  Alternatively, you could find a USB hub that supplies the 5 V line through its own power supply.


126  Using Arduino / Project Guidance / Re: Altimeter Interfacing on: September 29, 2012, 05:15:21 pm
I misspoke when I said it was only a logger, it also provides altitude data on a serial port here is the description of the serial port settings direct from the manual

"Serial port settings should be configured for 9,600BPS, 8 data bits, no parity, and 1 stop bit. Output data format from the altimeter is ASCII text based, with a <CR> and <LF> character appended to the end of each line."

So you could take the TX port on the logger and wire it to the RX pin on your Arduino and make sure the serial parameters on the Arduino match those stated above and you should be able to read the altitude directly and set thresholds in your sketch to trigger events based upon altitude.

127  Using Arduino / Project Guidance / Re: Altimeter Interfacing on: September 29, 2012, 04:33:54 pm
It does not look like your choice of altimeter allows for direct reading of the altitude as it just logs the data for analysis after the flight.  You could probably hack something if you had the schematics and/or the datasheet on the baro sensor used.

You might be better off starting off with MPXH6101A which measures pressure from 5 to 105 kPa, is 5 kPa low enough?  Although it is surface mounted module I have hon soldered quite a few of these very easily.  Build the basic circuit as shown in the datasheet and either take the output from that circuit directly into the ADC on the arduino.  If the 10-bit ADC does give you enough resolution run it into a separate 12-bit ADC and have arduino read that.

128  Using Arduino / Project Guidance / Re: Arduino + load sensors - sensing people jumping on: September 23, 2012, 11:38:35 am
The load cell you mentioned in principle would work you would probably need multiple cells to get the capacity required.  Most load cells require an instrumentation amp to amplify the signal coming from the wheatstone bridge inside the load cell.  I have had good luck using TI's INA122 for this type of application.  The output from the instrumentation for each load cell would be wired to analog input individually.  To read the total load (weight) you would read all of the load cells convert the voltage read to weight based upon your calibration data, add up all the weights after conversion.

129  Using Arduino / Sensors / Re: How to use RAZOR 9DoF AHRS for positioning on: September 22, 2012, 10:57:51 am
In most circumstances GPS will give you the position of a car much easier than an IMU.  Trying to get your position in an urban canyon with GPS can be difficult because you may not have large enough view of the sky to be able to connect to 4 or more sats, in this instance you may want to try an IMU and update the the position as soon as you get a GPS lock to correct the drift the IMU WILL have.

130  Using Arduino / Project Guidance / Re: PID library multi relay output on: September 20, 2012, 11:37:52 am
No comments on the code.  I wanted to add that solid state relays are great for applications like this.  I have gotten any number of good SSR's from ebay and Criagslist. 

One thing you must do is make sure you have a heatsink on the unit as it does not much inefficiency at 1000 Watts to toast out a solid state device.

131  Using Arduino / Project Guidance / Re: Reflow Oven Controller on: September 18, 2012, 04:41:49 pm
I think it looks good but you may want to have some additional LED's on the front panel, like one that goes on when the relay for the heater is turned on.  I built a large oven for baking guns and I wired in a 110V pilot light to show when it was heating maybe another one showing the temp is when a threshold of the programmed temp, ect.

132  Community / Products and Services / Re: Great PCB House for Prototyping on: September 13, 2012, 11:22:54 pm
The quicker turnaround than itead or iseed is what I really like, yes if you are producing any numbers the price hurts.
133  Community / Gigs and Collaborations / Re: Assistance request for motor control. on: September 08, 2012, 09:46:55 pm
This just ran through my little head how about RFIDs on each of the livestock?  Tagged they would be let through the gate if they approached the gate during the preset window.

Just some more or less random thoughts late at night,

134  Development / Other Hardware Development / Re: CPLD and Arduino - a good mix on: September 08, 2012, 06:11:26 pm
I ahve kind of curious about CPLDs as they seem like an amazing design space and would like to give them a try the only concern is a compatible programmer.  Could someone point me to programmers for that CPLD that I could use.  It seems like I have collected a few boards and programmers over that never quite mated up with a development environment, now I try to reduce the rate at which components go in the box.

135  Using Arduino / Microcontrollers / Re: Alternative to clock crystal. on: September 07, 2012, 05:16:46 pm

If you do not have the correct resonator in your grab bag let me know and I will drop a couple 16 MHz resonators in an envelope for you.

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