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Sensor Compatibility?!! — Parallax Forums

Sensor Compatibility?!!

billiam2536billiam2536 Posts: 28
edited 2009-07-07 13:17 in Propeller 1
I'm new with all the Propeller stuff, and upon fruitless searching, have one question. Are the Ardupilot and/or Paparazzi Thermopile xyz sensors compatible with the Propeller mc? Both boards are just modified FMA copilot xy sensors. They use thermopiles that are similar to the MLX90614 Infrared Thermometer Module's sensor. If they're not, is there a way to make them compatible? Thanks for any help, Bill.

Post Edited (billiam2536) : 6/29/2009 1:57:30 AM GMT

Comments

  • StefanL38StefanL38 Posts: 2,292
    edited 2009-06-29 16:41
    Hello Bill,

    I have never heard of that sensors before. (I'm no sensor specialist)
    If you provide information about the specifications of the electrical signal that is on the output of these sensors
    the forum can give you a detailed answer

    best regards

    Stefan
  • TimmooreTimmoore Posts: 1,031
    edited 2009-06-29 16:58
    The Paparazzi outputs a analog difference of 2 thermopiles. Looks like 0-3.3V from the schematic. Depending on the sensor you get between 1 and 3 analog outputs.
  • billiam2536billiam2536 Posts: 28
    edited 2009-06-29 17:03
    Alright, so would it work with the propeller?
  • Mike GreenMike Green Posts: 23,101
    edited 2009-06-29 17:08
    Yes

    Read the AN001 application note on the cog counters for information on analog to digital conversions. The sample code that comes with the AN001 shows how to do it, gives the tradeoffs between resolution and speed, and discusses how to choose the resistor and capacitor values needed.

    www.parallax.com/tabid/442/Default.aspx
  • billiam2536billiam2536 Posts: 28
    edited 2009-06-29 17:46
    Alright. I'm still a little lost (I am TOTALLY new to this), but I think I can figure it out. Just to be sure: Is it the Sigma-Delta ADC stuff on p17 of the PDF?
    Sorry for my slowness.
  • Mike GreenMike Green Posts: 23,101
    edited 2009-06-29 18:10
    Yes, the sigma-delta ADC stuff starts on p17. The ADC.spin source also has useful comments and is used as a library object to actually read the values.
  • Ole Man EarlOle Man Earl Posts: 262
    edited 2009-06-29 19:35
    If it is XYZ orientation you want, a Wii nunchuck is a 3 axis accelerometer and a Wii motion plus is a 3 axis gyro. Both interface to the prop via pins 28 and 29 the i2c interface. Simple to do and a 6DOF sensor for about $35.. Info on the forum.
    Earl
  • billiam2536billiam2536 Posts: 28
    edited 2009-06-29 20:31
    Wow, thanks for the info on the Wii controls. I had heard about people using the wii for parts and I have been looking into IMU stab., but it was looking pretty expensive. Thanks a bunch. Thanks for the clarification on the other sensors, Mike Green. I love the quick response times in this forum! It will make my project go much more smoothly.

    Post Edited (billiam2536) : 6/30/2009 1:25:10 AM GMT
  • billiam2536billiam2536 Posts: 28
    edited 2009-06-30 01:22
    What problems would I have if I use the ArduPilot IR sensor and the paparazzi z sensor together? Would the way they connect to the propeller board be different? What would I have to look out for?

    With the ADC, I will need a different circuit for each output signal, won't I? Or could I somehow work it all into one circuit?

    Sorry for all the questions, I'm just trying to figure out as much of this as I can before I dive into trial-and-error learning.
  • LeonLeon Posts: 7,620
    edited 2009-06-30 06:45
    If you have several ADC inputs, it might be best to use a multi-channel ADC. They are quite cheap.

    Leon

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  • billiam2536billiam2536 Posts: 28
    edited 2009-06-30 17:00
    If I use a multi-channel ADC, does it still need to be less than one inch away from the propeller pins, or would the adc IC keep the conversion separate from the cog counters all together?
  • Mike GreenMike Green Posts: 23,101
    edited 2009-06-30 17:03
    The one inch separation issue applies only to the built-in sigma-delta ADC. It does not apply to an external ADC.
  • billiam2536billiam2536 Posts: 28
    edited 2009-07-01 03:47
    In all honesty, I'm not sure what all the terms mean when looking for an ADC chip. Does anybody have a suggestion of what to use? I need at least 3 channels. Any setup tips are also appreciated.
  • TimmooreTimmoore Posts: 1,031
    edited 2009-07-01 04:00
    Depends on the number of channels, resolution you need, speed of sampling, etc.
    I have used the tlv2543 several times, It has 11 channels so it has more than you need, but its 3.3V so matches in terms of voltage levels. It is 12bit resolution and there is a driver available on obex. But there are a number of others available as well. One way is to go to obex and search for a2d and see what drivers are available.
  • billiam2536billiam2536 Posts: 28
    edited 2009-07-01 19:24
    Alright. What does resolution mean in terms of adc's? Does anybody know of an ADC that has at least 3 channels or just more than one, that has multiple outputs and performs simultaneous conversions of the analog signals, as opposed to have multiple inputs but one output that the converted signals take turns passing through. If this doesn't make sense, I may have misread my information. For me, the more stand-alone the conversion is, the better.
  • AribaAriba Posts: 2,690
    edited 2009-07-01 19:33
    There is an object in the obex for the Microchip MCP3208, an 8 channel 12bit ADC.
    This ADCs are relativly cheap and available in DIP-16 package.

    Andy
  • TimmooreTimmoore Posts: 1,031
    edited 2009-07-01 19:39
    resolution is how much detail - e.g. a 12bit ADC with a 3.3V input can give you ~1mv detail - i.e. any change smaller than that can't be seen. ADC tend to slow down with more resolution. They tend to come in 8/12/16bits. I find 12bits is good compromise. Fast enough, good enough. Noise in the system often shows up before you can more than 12bits of reo(expletive)ion so 16bits doesn't add anything.
    First time to look at before simanteous is speed of conversion - for example the tlv2543 takes ~10-20us to convert 1 channel, so 11 changes is 220us or ~4500 times/sec. This is much faster than the program can deal with the information. And almostly certainly faster than the sensor is changing the data. So I doubt you need simultaneous conversion. If you are taking the data, averaging to remove noise (say 8 samples), have 3 channels and can change the servos of your place 50 times/sec (the max a servo can do) then the max conversion rate needs to be 50*3*8 or 1200/sec and probably a lot less is good enough. The other reason for simulaneous is because you need to sample the sensors at the same time - I dont see a reason for this in your case. If 1 reading is 1/1200 sec after the other its not going to change the reading result enough to matter.
    So I would pick a 12bit resolution with at least 3 channels, I wouldn't worry about simultaneous conversation but look for conversion that is fast enough - 1 few hundred times a sec I would think is more than enough.
  • billiam2536billiam2536 Posts: 28
    edited 2009-07-02 01:06
    I know the single output is not a real restraining factor, but it would make programming simpler if there were three outputs because I'm still learning how to do the spin/asm programming. That's why I'm looking for a converter that is more stand-alone. But what ever, if there is a driver for it in obex already then its just as good.
  • billiam2536billiam2536 Posts: 28
    edited 2009-07-03 04:06
    Why do the different versions have different prices? What's the difference between them?

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    Working on getting money for autopilot project. Come check out my site if your interested in the project. Maybe go to the bottom of the page wink.gif

    Post Edited (billiam2536) : 7/7/2009 1:22:40 PM GMT
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  • Greg LaPollaGreg LaPolla Posts: 323
    edited 2009-07-03 04:43
    You will need to refer to the spec sheet for exact differences. I use This. It has a very easy to use driver in obex and its 3.3V so it interfaces seamlessly with the propeller.

    It appears that the differences are in the footprint/packaging. It would depend on your application SOIC being surface mount and DIP being through hole mounting.

    You can find a spec sheet in PDF here


    Greg
  • billiam2536billiam2536 Posts: 28
    edited 2009-07-07 13:17
    Alright, I have figured out all the differences between the chip versions and things like that. But, what's the difference between Σ-Δ ADC's and SAR ADC's like the MCP3208? What are the major pros/cons of the two?

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Working on getting money for autopilot project. Come check out my site if your interested in the project. Maybe go to the bottom of the page wink.gif

    Post Edited (billiam2536) : 7/7/2009 1:22:18 PM GMT
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