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Arbitrary Analog Sensor Tester

A tiny, Trinket Pro-based interface to test and/or calibrate various analog sensors.

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I hear the excuses "but testing takes too much set up!" and "but we can just calibrate it AFTER the flight!" far too often from inexperienced members of my HAB team. This mentality can lead to (and has caused) payload failure. My goal? Take those excuses away!

I'm putting most of the real content in project logs, but I figure this is a nice place to put design constraints, milestones, and specs.

Constraints:

  1. Smartphone-sized or smaller (shooting for smaller.)
  2. Purchase as few components as possible
  3. Must have a screen
  4. Must be compatible with 5V and 3.3V sensors
  5. Must be compatible with sensors which require an amplifier

Specs (derived from constraints):

  1. Hackaday.io Pro Trinket (5V) microcontroller
  2. 9V battery for power (Constraint #2)
  3. LM317 voltage regulator (Constraint #2) (Sensors not powered off of Trinket regs)
  4. 741 Op-Amp for amplified sensor input (#2)
  5. Adafruit 1.8" TFT display
  6. Block terminals for: +V, GND, Unamplified In, Amplified In
  7. Switches for: On/Off, 3.3V/5V logic
  8. 10k pot for op-amp gain control
  9. Rotary encoder with pushbutton switch for UI

Current Milestones:

  1. Buy all components that I don't have
  2. Think of a better project name
  3. Draw up a schematic. By hand. In the back of a notebook.
  4. Start prototyping!

  • Woah, What Happened?

    AngusJimiKeith12/24/2014 at 18:58 0 comments

    Well, I haven't updated this project in three weeks. What did happen? And what's the status of the project?

    Well, basically, it all exploded.

    Quite literally the day after I posted this project, both of my major projects heated up at the same time. Sadly, that pushed this back until I had free time again. But, alas, what happens in mid-December for college students? Yep, you guessed it: final exams.

    As a result, I've had no time to do anything related to this (or any other fun side projects, for that matter!)

    So, to the important question: where does that leave this project?

    • I don't have time to finish before the challenge deadline. I will not be up for the prize.
    • However, for reasons explained in my previous project log, this tester needs to be built.
    • Over break, I don't have access to most of my electronics stuff. I have a small bag'o'components, the Trinket, and a couple breadboards, but not enough to put together a finished product.
    • However, I have passed this idea along to other members of my near-space team. One of them who does have time and supplies over break will be working on it.
    • With the sort-of-new direction, I do not know how often I'll be able to update, but the project is not quite dead.


    Thanks to the couple of people who followed, and I hope to share more projects (with less delays!) in the future!

  • Well, here goes nothing...

    AngusJimiKeith12/02/2014 at 06:00 0 comments

    Once I finally decided "ah, what the heck, I'll take a shot at the Hackaday Trinket contest," my actual project idea came pretty quickly. Here's the in-depth explanation of what I'm doing and why I'm doing it!

    The problem:

    I spend quite a bit of my "hacking" time working on high altitude balloons with my school's aerospace engineering department. It's an awesome project, amazingly fun, we get to build actual flight hardware, all the bells and whistles. Of course, not everything always goes to plan (when does it ever?). One of the larger issues we end up combating is faulty or incorrectly set up sensors. The lab we use as our mini-makerspace has been home to the HAB program since its inception more than a decade ago - and several of the leaders of the program in that time were notorious hoarders. The end result? Literally dozens of sensors, mostly simple analog breakout boards, that may or may not still work. Since no one wants to spend money on a new sensor, these things get used and abused way too many times to count. I'm fairly certain that I've even seen a payload that consisted entirely of discontinued products. I wish that were hyperbole.

    This is all well and good except for a few inconvenient tidbits. First, the people who usually grab old sensors are by and large our newest, most inexperienced groups. They're usually cobbling a payload together with what bits they can find in the lab and what code they can find online. Almost universally, this means that they don't really bother testing or calibrating anything. The most common excuse, which persists even after being shown how to test or calibrate a sensor, is "That takes too much time, I don't want to set it up!".

    My solution:

    My solution to this problem is simple: create a plug-and-play sensor tester. For the inexperienced new guys, the setup time, and especially the super scary code (the horror!) will be taken out of the equation, and they'll have a better shot at a successful first payload. And trust me - a successful first payload is key to retaining interest! For the program's veterans, including me, we'll have a quick setup to test the piles of sensors lying around and perhaps thin out the collection a bit. Additionally, even we complain when we have to breadboard a circuit just to test something for 30 seconds. Cutting setup time increases test time, and more testing is always good.

    Another advantage is calibration. No two sensors are perfectly alike, and it can show! One of the most striking examples of this that I've seen happened just last month. An analog accelerometer, using the datasheet's conversion from voltage to G force, reported Earth gravity as 1.2 G. That's...not exactly insignificant, especially when the sensor is being fitted to a prototype shock absorber! However, once we knew about that inconsistency, we could easily correct for it in our code. The downside was that in order to calibrate, we needed to assemble the payload, run the Arduino for a minute or so, disassemble the payload, remove our logger's SD card, and pull the data off of that. Wouldn't it be simpler to just plug in to a pre-built tester and get instant results? I certainly think so!

    As you can see above, I've already specced out pretty much everything for this project. Tomorrow, I'll write up another update with an in-depth look at the design so far.

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PointyOintment wrote 12/02/2014 at 06:02 point
As somebody who's never done any HAB stuff, I'm surprised that people who do think it's a good idea to wait until after the flight to calibrate instruments. First, that's just procrastination. Second, you might not get those instruments back to be able to calibrate them after the flight. Third, if those instruments are being used for any kind of real-time control/decision-making, they'd better already be calibrated when you try to use them for that. Hopefully you succeed in helping your team be more willing to calibrate the instruments. :)

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AngusJimiKeith wrote 12/02/2014 at 06:11 point
You have no idea...We are generally talking about college freshmen here, but I can't count the amount of times in the last few months I've said "You did WHAT?!?!". Luckily, there isn't any active control stuff done by these less experienced groups! It's a little disheartening to see teams report failure after their first attempt because of procrastination and/or not knowing better, hence this project (one of several we have going on to bolster our freshman program right now!) Here's hoping! :)

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