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Thread: Teensy 3.6 Expansion GPIO Board

  1. #1
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    Teensy 3.6 Expansion GPIO Board

    Does there exist a Teensy 3.5/3.6 expansion GPIO board? I know the 35/36 series has a lot of IO pins now but my project will need 73 IO pins. I was just wondering if there already exists an IO expansion board or if Paul has ever thought about creating one?

  2. #2
    Senior Member+ defragster's Avatar
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    Other than PCB's that bring the lower pads to pins for use.

    Other solutions depend on the need for digital or analog GPIO?

    I found this thread : Potentiometers-affecting-each-others-when-connected-to-74HC4051

    With a forum search for 'multiplex'.

    Or you could add a second T_3.5/3.6 and use SPI_MST to connect them and get near 71 using SPI_MSTransfer

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    I continued to do some searching found this: http://land-boards.com/content/index.php/digio128

    It uses 8 MCP23017 chips on a board to provide 128 GPIO pins. Now, that's enough IO pins! A bit pricey at $75.00, but I understand the hardware production costs, etc.

    I'll have to stick to using my own MCP 23017 chips for now.

  4. #4
    What exactly do you need, or trying to accomplish? For certain cases, you could just use some 3-to-8 or 4-to-16 multiplexers. A lot cheaper than the digio board you linked.

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    I'm building a flight simulator control panel: 32 push buttons, 5 dual rotary encoders w/push switches and 2 single rotary encoders with push switches.

    I've mapped out all the pins needed and I can do this project using all the available top side pins on a Teensy 3.6 and three MCP23017 chips.

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    Senior Member+ MichaelMeissner's Avatar
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    If you are doing a one-off project with through hole soldering, and could down grade one of your MCP23017's down to a MCP23008, the busboard SB830 would allow you to mount the Teensy 3.6 on the board, and provide ground/3.3v power rails down each side. This would allow you to 2 or 3 male/female headers to connect each pin/encoder separately:


    The Adafruit full size Perma proto board might be useful as well, but you would need to deal with one of the MCP boards hanging off the end by one pin:


    Also the large Azzy's Electronics prototype board might be usefu (you would stagger the Teensy and MCP's one different ends, so that each could bring out the 2 power rails and pins):


    Note, the SB830 is single sided, which means you have to solder all of the headers/pins/etc. on one side. The Adafruit and Azzy boards are double sided.

    However, it is a large amount of soldering to solder in the male or female headers, and to make sure each pin is connected and you did not create solder bridges.

    If you can group your switches, I would think using either RJ45 jacks (8 wires) or IDC wire packs (2x3, 2x5, 2x8, etc.) would work better rather than having 48 separate connections, each of call fall off/wire break, etc.

    For example, if you are using the Azzy board, you could put the Teensy and each of the MCPs at the left side of each of the mounting area, and put several of these 2x8 shrouded box mounts at the right side, and use a 16 pin IDC cable to go to each cluster of pins:


    The shrouded box cables are nice in that they are polarized (i.e. you can only insert the cable in one direction).

    You probably need to group the i2c reads so that you poll all 16 pins at a time, rather than polling each individual pin separately. If you have some left over digital input pins on the Teensy, you would probably want to use the interrupt pin from the MCP23017 to know when at least one of the buttons from the MCP has changed state.

    The alternative would be to create your own PCB, but this probably take some amount of time to learn the tools and to wait for the PCB makers to send you the boards.

    <edit>
    I just recalled that the Tall Dog boards now have carrier rails on the sides. Even if you don't use it to bring out the underneath pads, you can use these carrier rails for providing power/ground/IO for all of the pins (you would to connect the three MCP's on a separate board -- and you probably need to think of adding pull-up resistors for SDA/SCL):
    Last edited by MichaelMeissner; 06-26-2018 at 09:40 PM.

  7. #7
    You could always use a matrix for your input buttons. Either 6x6 driven directly by the Teensy or a single 8bit serial to parallel chip for the driver side and 4 inputs for the read.

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    Thank you all for that information!!

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    i got a few of these that i played with in past, sure theyre for the PI, but after tracing the lines on the connector i had it working in teensy. they have both spi &i2c variety, but spi is faster, i dont bother with i2c version

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    its actually smaller than the board you posted in post#3, fits in palm of hand, smaller than my hand actually and all interrupt pins are available for use

    (MCP23S17) spi version
    (MCP23017) i2c version

  10. #10
    Senior Member+ MichaelMeissner's Avatar
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    Tonto81, it might be helpful to post a link to the actual board (or least mention who made it).

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    i didnt want to spam/advertise, im not affiliated with them i just ordered off their ebay page

    https://m.ebay.co.uk/itm/Rs-Pi-I-O-i...kAAOSwr41XH-Qj

    only exists for the PI but if you can trace the lines of the Pi connector to at least 1 chip on there like i did youll find the spi lines, whats nice about this board is all the chips run 3.3volts logic, perfect for teensy 3.6, you can use sumotoy’s library with it after, me i just access the spi writes directly

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    Senior Member+ MichaelMeissner's Avatar
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    Thanks. I was trying to find the board, but I only found separate MCP23017/MCP23S17. That is a lot of i2c/spi devices.

  13. #13
    Senior Member PaulStoffregen's Avatar
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    Quote Originally Posted by rfresh737 View Post
    I was just wondering ... if Paul has ever thought about creating one?
    Yup, I've certainly thought about this. I've thought about a lot of things...

    Many times Robin & I have talked about possibly creating a huge line-up of shields & accessories, sort of like Adafruit did over the last couple years for their Feather form factor. From a business perspective, that's probably one of the more profitable directions we could take.

    Instead, I put about 4-5 months of work this year into greatly improving how we do USB communication, and a number of other software improvements. I'm also working on Teensy 4.0. Whether these are good choices business-wise is a hard question. But they're things I want to do. I also really want to work on a huge list of other software features, especially on audio and eventually motion graphics. Hardly anyone in the Arduino/maker/hobbyist world is putting much work into those sorts of things, because making lots of hardware to sell is where the money is.

    So, the answer is yet. I have indeed thought about it.

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    Thanks for that input Paul.

    I find that these 'Ardunio style' boards are mostly good for testing code and 'small' projects. I'm a retired pilot instructor and my hobby is flight simulators. I'm building a small control panel, but in the flight sim world, small still means needing a lot of IO pins because cockpits have a lot of switches and knobs! As the Teensy's get more and more powerful their capabilities start to look better and better for this hobby. In my situation, I'm interfacing with a computer monitor so your mouse library with the capability to put the cursor on a specific spot and do a mouse click is vital -- and -- Teensy is the only board (that I know of) that can do that. Ardunio boards cannot because they don't support absolute mouse positioning. They have an extremely clunky way of implementing that same feature but it's a mess! Thank God you wrote a real mouse library!

    The other short coming with ALL of these boards is sketch upgradability in the field. Perhaps this is the most significant short coming of all. If I were to build a flight simulator control panel and sell it, I only have very ugly ways to upgrade it in the field with a new sketch. So, what this means is that these boards are only really useful and fun...to use at home...where you can easily change the sketch when you want to. The IoT boards (Particle) have a wonderful online admin control panel where you can monitor every board you have fielded and can control sketch updates online! A PERFECT solution...the bad news is that the Particle board capacity is so small and under powered, etc. it's not useful for any projects that need a lot of IO pins and a lot of power (like the 3.6 has).

    We don't need to be able to update our boards in the field online like the Particle can (it would be nice but that's a lot of work to build that)...but what we could really use is the option to mail our customers a new SD Card with the new sketch on it and simply have the customer R&R the SD Card on the Teensy 4.0. Maybe a pin on the board to control allowing or block this capability. So now, when the Teensy starts up, it looks for a fixed name file on the card and loads that sketch upon start up each time. That would be enough to solve the field upgradability problem.

    I think a whole new market could open up for the teensy boards as they become more and more powerful and support more and more IO pins. Yes, we don't need a Teensy to have 128 IO pins on its own board (I personally wouldn't mind!) but being able to buy an add-on shield or add-on external board from you that would give us 128 more IO pins would be welcomed...and have it so we can chain more expanders onto that one so we can use Teensy for large projects. I guess what I'm saying is that more thought should go into these boards to get them out of the 'home-only hobby environment'...to allow them to really be used beyond being just a hobby...to be able to sell what we build and then be able to upgrade them in the field without needing a PC to flash them. That's too much to ask a customer to do who only use a PC to check their email!

    In summary, I know these idea's all take time...a lot of time...and you're a one man shop...so you can't do them all. There is never any shortage of folks telling you what the Teensy 4.0 should have on it. After all, everyone likes to dream! No matter what the Teensy 4.0 turns out to be, everyone will like it.

  15. #15
    Quote Originally Posted by rfresh737 View Post
    T
    I think a whole new market could open up for the teensy boards as they become more and more powerful and support more and more IO pins. Yes, we don't need a Teensy to have 128 IO pins on its own board (I personally wouldn't mind!) but being able to buy an add-on shield or add-on external board from you that would give us 128 more IO pins would be welcomed...and have it so we can chain more expanders onto that one so we can use Teensy for large projects.
    It should be possible to add connections to extra I/O pins.

    There are high density mezzanine connectors that can bring out 60+ pins in a small package -- there wouldn't be enough place for them on the smaller Teensys (3.2, LC) but they could be used on the bigger ones.

    There are many different types, here is one product brief: https://www.hirose.com/product/en/do...22&is_series=1

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