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Thread: Analog Input Count

  1. #1
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    Analog Input Count

    Paul || PJRC peeps:

    I have a project that would require exactly 27 analog inputs (and 4 digital inputs). From what I can see in the documentation, the 3.5 has 27 analog ins? I'm trying to figure out where they all are from the pinout diagram. Just trying to determine if I can make this work without doing the multiplexer setup. Would prefer to have everything directly connected for simplicity.

    https://www.pjrc.com/teensy/card8a_rev2.pdf

  2. #2
    Senior Member+ defragster's Avatar
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    Looking at the card backside are 6 more labelled to add to the 21 on the front edge pins.

    The other six:
    4 are internal pins on T_3.5 and 2 are on bottom pads

  3. #3
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    Quote Originally Posted by defragster View Post
    Looking at the card backside are 6 more labelled to add to the 21 on the front edge pins.

    The other six:
    4 are internal pins on T_3.5 and 2 are on bottom pads
    What does "internal" pins mean? Soldering onto the pads isnt a big deal, but how would you access "internal pins"?

  4. #4
    Senior Member+ MichaelMeissner's Avatar
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    Quote Originally Posted by atf104 View Post
    What does "internal" pins mean? Soldering onto the pads isnt a big deal, but how would you access "internal pins"?
    Look at the Teensy from the top with the USB facing right (i.e. the third image in https://www.pjrc.com/teensy/pinout.html).

    On the second row from the top, you will see 4 holes that take up the first 0.6". You would solder wires or headers to these holes. Starting from the right you have:
    • No hole under the VIN pin;
    • VUSB under the Analog Ground pin (this is the power straight from the USB header that usually is connected to VIN);
    • No hole under the 3.3v pin;
    • AREF (analog reference) under the A9/23 pin;
    • A10 under the A8/22 pin;
    • A11 under the A7/21 pin.


    Then look at the row of pins in on the right side (in the 3.6, these would be the second USB pins, but in the 3.5, they are the other 2 analog pins):
    • There is no hole just over the ground pin;
    • There is no hole just over pin 0;
    • There is a hole near pin 1, but it is not used;
    • There is a hole near pin 2 that is A26;
    • There is a hole near pin 3 that is A25;
    • The remaining two holes near pins 4 and 5 are ground pins.


    It is unfortunate that the last set of pins are not aligned to a 0.1" boundary, so that you could add sockets from a protoboard.

  5. #5
    Senior Member+ defragster's Avatar
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    Quote Originally Posted by atf104 View Post
    What does "internal" pins mean? Soldering onto the pads isnt a big deal, but how would you access "internal pins"?
    @MMeissner did a good job on details - just meant 'internal' on the PCB - inset from the edge pins where they are 'called out' on the bottom side of the T_3.5 card - with the 'light orange' flag boxes used on the other analog signal pins

  6. #6
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    Thanks everyone!

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