Solar Empire

Today I was messing around with my electronics again.

The Georgia Tech structures lab has a Vishay 7000 strain gage DAQ designed to read several strain gages. I had been using it for my dissertation research, in experiments at GTRI. Recently, though, it was suggested that it might not be available for my research in the future. I believe that has since been resolved.

However, I had started a parallel effort involving designing and building a wheatstone-bridge amplifier circuit for a strain gage daq. If I couldn’t borrow a unit from school, and I wasn’t allotted the budget to purchase a commercial DAQ, I wanted to see if I might be able to build one from board-level parts.

Strain gages are small resistive patterns of wires, usually embedded in foil, which are attached to a surface. When the underlying surface deforms, minute changes occur in the resistance of the pattern. These changes in resistance are usually measured by means of a Wheatstone bridge. A Wheatstone bridge is a circuit that allows you to null out a reference resistance and measure changes in the resistance of the strain gage. The bridge consists of four resistors: Two on the balance arm, and two on the measurement arm. On the measurement arm, one of these is the strain gage. On the balance arm, one of the resistors is an adjustable resistor that allows zeroing of the signal.

For a 350 ohm strain gage, with a gage factor of 2, for strains of 0.1 microstrain, changes in resistance are on the order of 7E-5 ohms: very small! These changes in resistance will result in changes in voltage (for excitation voltages of 2V) of 0.1 microvolts. In order to read this signal, the bridge excitation voltage must be amplified by 10000 times or so.

(PS: All you EEs out there: Stop laughing! This is my first time playing around with op-amps. I’m well aware that there may be issues with noise and variability in the resistors).

By the time the Vishay schedule was resolved, I had already designed a lot of the circuit, and ordered a lot of the parts. Today, just to see what I could do with the parts I had on hand, I began to assemble the Wheatstone bridge/amplifier unit.

I 3d printed the front panel of the device: Here you can see the assembled front panel. The phone-jack is the input terminal for the strain gage (structures lab wires its strain gages into RJ25 plugs, which is what the Vishay uses for its input terminals). The potentiometers are a series of pots that allows the bridge to be balanced by adjusting R3 on the balance arm. The two bannanna-jacks are where I’ll probably plug in a real lab voltage meter after I give up on my DAQ.

DAQ front panel

Electronic Cthulhu

PS – soldering leads to that RJ25 plug? Very fiddly. Check this out: As my Air Force friends might say, ‘rocket surgery’.

(PPS – quit laughing EEs! I didn’t have a nice breakout PCB to plug it into.)

What I worked on mostly today: I wanted to see if I could build my own reader for analog signals such as the strain gages. I have an Arduino Mega, which has it’s own ADC built in, but I wanted to see if I could communicate with a commercial ADC chip using my Raspberry Pi (which only has digital IO pins). The Raspberry Pi is nice because I can command it to do things wirelessly by logging in via SSH. The Raspberry Pi is a full Linux PC, and you can program routines to interact with the IO pins in high level languages like Python.

Do you cut the red wire or the green wire? They’re all green wires! Muahahaha.

The ADC chip I’ve been using is the relatively cheap LTC1286. I managed to bit-bang the LTC and read the output from it successfully. There are a few things I might need to tweak. Right now, I am using a battery to supply voltage to the voltage reference pin – if I want to do this right, I’ll need to regulate the reference voltage somehow, as the refrence voltage governs the full-scale of the ADC. Without precise control of the reference voltage, you won’t have exact knowledge of what the binary output of the ADC means in terms of input voltage.

I’ll also need to play around with what I’ve been doing: There appears to be a lot of noise for something that is supposed to have 12 bits of resolution. (4096 levels between bottomed out and full scale, for those non-engineers reading this.) Here you can see me dialing the voltage divider up and down with the 100k pot attached to the circuit.

Noise. Also, signal.

Finally: The mess! I can’t wait until I have actual workspace, so I don’t have to use my bed as a bench.

Also, here is a link to the python code I wrote to bit-bang the ADC. (To send the right clock signals to read the output from the chip.)
test_ADCread2.py

I’m just in grad school. 😛 The past year has been very busy, but I’ll try to post here more often. I’m actually trying to spruce up the main website, amssolarempire.com a bit to show off my projects. Apparently prospective employers look for things you’ve done to be shown off on social media these days.

Some thoughts of mine on space logistics from a comment:

If you want to use something like nuclear thermal or solar-thermal rockets to push cargo and eventually people around the solar system (to, say, actually set up a base on the moon/mars), then hydrogen is what you will need for propellant.

Reading the research on lunar water deposits a few years ago, I didn’t get the impression that there was a lot there. The article discussing the orbital neutron reflection scan seemed to imply something like an extremely diffuse presence in tons of sand in the permanently shadowed regions of the moon. If so, blowing it away as reaction mass might not be sustainable. You might want to keep it around for use in moon-bases.

Ceres seems to be the closest object with lots of water and a shallow gravity well. (It’s also, and for that reason, far enough out that deriving serious power from solar energy is problematic.)

I think that colonizing Mars / beginning to fling large masses around the solar system with space derived propellant, may require robotically colonizing Ceres as a first step.

Your daily dose of science fictionesqe cosmic horror:

I hear a lot of references to things like hive-minds (a concept that is seldom well presented) or the internet “waking up” someday and beginning to have thoughts of “its own”.

I submit to you that this has already largely happened. It’s just not the profound/powerful event that people suppose – instead it’s banal. Look at the comment threads under any given article written by actual single human beings and notice the difference between something authored by a person with a name and something authored by “the internet”. Look at the uniformity, across articles and topics of the nature of the comment thread spam.

We’ve already met the “hive mind” of internet connected humanity. It isn’t deep, it isn’t bright, it isn’t even sane. It’s this guy:

“I am fully conscious that, not being a literary man , certain presumptuous persons will think that they may reasonably blame me; alleging that I am not a man of letters. Foolish folks ! do they not know that I might retort as Marius did to the Roman Patricians by saying: That they, who deck themselves out in the labours of others will not allow me my own. They will say that I, having no literary skill, cannot properly express that which I desire to treat of but they do not know that my subjects are to be dealt with by experience rather than by words and experience has been the mistress of those who wrote well. And so, as mistress, I will cite her in all cases.

Though I may not, like them, be able to quote other authors, I shall rely on that which is much greater and more worthy:— on experience, the mistress of their Masters. They go about puffed up and pompous, dressed and decorated with [the fruits], not of their own labours, but of those of others. And they will not allow me my own. They will scorn me as an inventor ; but how much more might they— who are not inventors but vaunters and declaimers of the works of others – be blamed.”

Apparently at one time, it needed to be said. (As for him not being a literary man, he then proceeded to write what would have been one of the first textbooks on optics and perspective had it been widely distributed.)

Cool machine learning project:
https://www.youtube.com/watch?v=xOCurBYI_gY#t=279

Now, if I were an alarmist journalist, I would make some claim like: “In the future no one will be able to play videogames because we can make computers that play them better. Video-game players will become obsolete! What will we do with all the useless gamers?”

Here is an interesting math paper that I wrote for a class on Ordinary Differential Equations. The subject is Ergodicity and the Fermi Pasta Ulam system. In 1955, Fermi, Pasta and Ulam wanted to investigate the behavior of nonlinear systems. Nonlinearity had always been suspected of a particular behavior: the dense filling of a configuration space’s energy level surface over a long period of time. Assumptions that followed from that lead to many results in Statistical Mechanics, as well as some paradoxes and problems.

What Fermi found was that oftentimes, nonlinear systems don’t produce anything like ergodic behavior, or equipartition of energy, as was assumed. There may be many unappreciated consequences of this, due to the relative inaccessibility of the behavior of nonlinear systems with many analytical mathematical tools.

Anyway, here it is:
Schinder_MA6307_SemProjReport

The ESA space probe Rosetta has successfully landed a lander on a distant comet today. Futher information can be found at:

http://www.esa.int/Our_Activities/Operations/Live_updates_Rosetta_mission_comet_landing
Tweets by ESA_Rosetta
http://www.dailymail.co.uk/sciencetech/article-2831125/Rosetta-mission-broken-thruster-computer-glitch-scupper-today-s-historic-landing-comet-67P.html

Comet 67P, on which the Philae probe successfully landed. Due to the minimal gravity, Philae secured itself to the surface of the comet with a harpoon and landing screws.

Congratulations Rosetta team!

The unfortunate trouble with minecraft:

This is roughly a full days work.

I once dug a wiring trench through sandstone, roughly 4 ft deep by 4 ft wide by 8 ft long once with a pickaxe. I was sore for a week afterwards.

PS – if anyone is interested in my minecraft worlds, I host one at www.amscyberpunkatlanta:25565.

MultiMC is a program allowing you to launch packaged instances of mods and settings for minecraft. A MultiMC instance allowing you to log into the server is listed on the server status page: http://www.amscyberpunkatlanta.com/MCWstatus/serverstatpage.php

“The thickness of the proposal required to win a multimillion dollar contract is about one millimeter per million dollars. If all the proposals conforming to this standard were piled on top of each other at the bottom of the Grand Canyon, it would probably be a good thing.”