Neo-Non-Conceptual Art

If....

* Jeff Koons can afford an atelier of assistants to polish his balls;

* Urs Fischer can hire someone to construct a set of autonomous office chairs;

* Mauricio Catellan can be praised for his Duchampian wit, a century on;

* Darren Bader can get a warm review in the Times for his re-heated thoughts;

Then....

It seems that even the ideas of post-post-modern artists' are of little utility.

Therefore....

Along with no longer producing anything of intrinsic value, I should also outsource the conceptualizing. Surely there are artists in other countries who can have ideas much more economically than me?

After that, given its glaringly short supply in the developed world, I might as well suspend my judgement as well.

So, from here on in, just assume that, if I had thought it was worth the effort, I would have done it.

Already....

and for completness sake

A short Variations Too documentation video from Currents 2019 in Santa Fe:

(many thanks to my spokes-model, Raina Wellman!)

Variations Too -- The Program

I seem to have (finally) come to a rest in the development cycle of the Variations project so I thought I should post the actual Arduino code, for completeness sake....

VariationsToo.zip

You will also need all (or most of) my previously described libraries:

schipArduino.zip

I had to give up on the HCSR04 sonar distance detector because it was unreliable, noisy, and sensitive to vibrations when the arm servo motors were running. I replaced it with my old favorite, the GP2Y0A02YK (or equivalent) IR distance sensor that triggers out at about 2 meters. This only needs an ADC channel to interface, so it's a lot simpler anyway.

Variations Too will be in:

CURRENTS NEW MEDIA 2019

in Santa Fe, NM, from June 7 - 23. So come on by!

...You and I both have to wait until the piece is installed in the gallery before I can make a decent video because I have run out of room for clean backdrops in my home/studio...

Random Thought

I have to say, that, in general, I do not believe in randomness. I'm sure there are some Quantum Mechanics (Maniacs?) out there who will beg to differ and provide supporting arguments, but until then....

Let's say I flip a coin. This particular flip comes up HEADS. Can you provide me with a proof that it could have been TAILS? Sure, sure, you can show that the next few flips might have different outcomes, and further that the next 1 billion flips will average dangnabbitedly close to 50% each. But that's not what I asked. I want proof that the original action might have taken a turn to the T-side. Since that has already (not) happened it is in the -- still apparently -- inviolable past and cannot be changed. So maybe it wasn't random at all?

Don't get me wrong, I'm not trying to argue that we can predict the future. Both complicatedness (many moving parts) and complexity (intersecting feedback loops) make that practically and theoretically impossible.

I'm just saying that we can predict the past.

Fixed Point Failure

A Fixed Point math library and Neural Net demo
for the Arduino...

Or: Multiple cascading failures all in one place!

Last year I found a simple self-contained Artificial Neural Net demo written for the Arduino at: robotics.hobbizine.com/arduinoann.html and spent a goodly amount of time futzing around with it. I now, almost, understand HOW they work, but have only a glimmering of insight into WHY. The demo does something really silly: The inputs are an array of bit patterns used to drive a 7-segment numeric display and the outputs are the binary bit pattern for that digit (basically the reverse of a binary to 7-segment display driver). Someone not totally under the influence of ANNs could do this with a simple 10 byte lookup table. But that is not us. On the plus side it _learns_ how to do the decoding by torturous example, so we don't have to bother our tiny brains with the task of designing the lookup table.

HOW ANNs work on the Arduino is:

• a) Extremely slowly, because they use a metric shit-ton of floating point arithmetic; and,
• b) Not very interestingly, because each weight takes up 4 bytes of RAM and there is only about 1Kb kicking around after the locals and stack and whatever else is accounted for -- the simple demo program illustrated here uses about half of that 1K just for the forwardProp() node-weights and then the backProp() demo uses the other half for temporary storage. Leaving just about nothing to implement an actually interesting network.

But. I thought I could make a small contribution by replacing the floating point -- all emulated in software -- with an integer based Fixed Point implementation -- whose basic arithmetic is directly supported by the ATMEGA hardware. This would also halve the number of bytes used by each weight value. Brilliant yes?

And in fact. My FPVAL class works (see below for zip file).  Except, err, well, it doesn't save any execution time. But more on that later....

Anyway. The FPVAL implementation uses a 2-byte int16_t as the basic storage element (half the size of the float) and pays for this with a very limited range and resolution. The top byte of the int16 is used as the "integer" portion of the value -- so the range is +/- 128.  The bottom byte is used as the fraction portion -- so the resolution is 1/256 or about .0039 per step. On first blush, and seemingly also in fact, this is just about all you need for ANN weights.

As it turns out, simple 16 bit integer arithmetic Just Works(TM) to manipulate values, with the proviso that some judicious up and down shifting is used to maintain Engineering Tolerances. This is wrapped in a C++ class which overrides all the common arithmetic and logic operators such that FPVALs can be dropped into slots where floats were used without changing (much of) the program syntax. This is illustrated in the neuralNetFP.cpp file, where you can switch between using real floats and FPVALs with the "USEFLOATS" define in netConfig.h.

Unfortunately it appears that a lot of buggering around is also needed to do the shifting, checking for overflow, and handling rounding errors. This can all be seen in the fpval.cpp implementation file. An interesting(?) aside: I found that I had to do value rounding in the multiply and divide methods -- otherwise the backProp() functions just hit the negative rail without converging.

I also replaced the exponential in the ANN sigmoid activation function with a stepwise linear extrapolation, which rids the code of float dependencies.

I forged ahead and got the danged ANN demo to work with either floats or FPVALs. And that's when I found that I wasn't saving any execution time.  (Except, for some as yet unexplained reason, the number of FPVAL backprop learning cycles seems to be about 1/4 of that needed when using floats[??]).

After a lot of quite painful analysis I determined that calling the functions which implement the FPVAL arithmetic entail enough overhead that they are almost equal in execution time to the optimized GCC float library used on the ATMEGA. Most of the painful part of the analysis was in fighting the optimizer, tooth-and-nail, but I will not belabor that process.

On the other hand, if you are careful to NOT use any floating point values or functions, you can save two bytes per value and around 1Kb of program space. Which might be useful, to someone, sometime.


So. What's in this bolus then is the result of all this peregrination. It is not entirely coherent because I just threw in the towel as described above. But. Here it is:

http://www.etantdonnes.com/DATA/schipAANN.zip

Some Driveline Enhancements

Variations Too, again

So. I've been dragging my feet -- once again -- because everything just seemed too hard over the holidays, but I have made progress none-the-less....

While doing limited in-camera demos I found that the Variations second arm linkage just tore itself apart pretty consistently. This was due to there being nothing but a bit of stickyness holding the axle into the arm. I originally used two pins through the whole sandwich to keep the gear from spinning, but I didn't have anything really holding the layers together, and there was too much torque for the sticky to manage.

This has, perhaps, been remedied:

Improved(?) axle mounting

After the arm was all re-assembled, I drilled a hole longitudinally through the circular backing plate and the axle, and glued a 1" long by ~1/32" diameter nail into the hole. This of course requires solid drill press, or mill, mounting and careful attention to not breaking the (@$!@#) miniature drill. Here you can also see the two pins (little brass brads, also about 1/32" dia) that pierce the entire sandwich to prevent the gear from spinning on it's own.

Compare to the previous layout, where the above photo is looking straight on from the bottom:

So. After assembling and gluing all the little bits into their sandwich, one needs to fire up the machine shop and drill two transverse holes almost through all of plate-arm-gear layers -- the almost part being that we don't want to completely pierce the gear itself, thus the pins need to be shorter than the full thickness (which may vary according to the arm material). Then rotate the arm and drill a longitudinal hole through the backing plate and axle -- basically straight down, centered where the "Plexiglas backing plate" arrow points in the above -- Gear Linkage -- photo. THEN glue the relevant pins into the holes. I've tried both: Goop, which is a bit hard to get schmushed into the holes but sticks to the pins; and: filled acrylic-solvent glue, which can be squirted into the holes but only sticks to the pins in an advisory way. Fortunately the sticky provides little in the way of mechanical advantage, it only needs to keep the pins in place.

I did this for the two lower arm linkages and made the executive decision that the torque on the smallest, upper, arm did not merit the extra effort. YMMV...

 

So.

I think this may be the end of the mechanical portion of our time together, save perhaps for cable routing which is still rather ad-hoc.

Sonar! The HCSR04 Library

For Variations Too I need some kind of distance sensor to see if there is anyone watching and how interested they might be. For the 'real' Variations I am planning to use a video camera and image processing, but this is the kiddie version.

So...

I thought I had it all worked out because I've used this cheapo, err, inexpensive, HC-SR04 (aka 19605-UT) ultrasonic sensor, from mpja.com amongst, in other projects using my MSCapture library which turns Arduino Pin 8 into a Timer 1 counting input -- remind me to rant about this sometime, especially since my library is perfect for grabbing IR remote control signals -- but for now.

See the data sheet here.

But, if you've been reading along, you know that the Servo motor control library is also a big fan of Timer 1 and thus that acre of digital real estate is no longer available. So I had to reinvent the wheel using a different mechanism with Timer 2 which has only an 8 bit resolution and no external count input.

Therein lies the HCSR04 library in my code bolus.

It uses three interrupts (you are surprised?), two from Timer 2 and one from an external pin change signal. The counter is run with the maximum pre-scale of /1024, giving a 64 micro-second resolution which is not quite as fine as one would like, but it turns out that the sensor itself is not quite as fine as one would like either, so it sorta works out. It counts the timer overflow interrupts to add 4 more bits to the timing range, which is somewhat more than enough to detect the SR04's no-signal failure signal.

Two digital pins, and power, are connected to the sensor. One pin is the Trigger output which can be any available digital output pin. It sends a short positive pulse, where the falling edge starts a sonar sample cycle. The other is the Ping input pin which goes high from the end of the sonar ping until it gets an echo response -- or for a loooong time if it misses the echo (more below). The Ping input currently has to be Arduino Pin 2 or 3 -- because I couldn't make sense of the doc for attachInterrupt(), I think one can use other pins but the code will need a light re-wanking.

HC-SR04 signals

The library class has these methods:

    /** default constructor **/
    HCSR04();   

    /** initialize the HC-SR04 sensor pins and timer interrupts
     **  leaves all the interrupts disabled
     **   use SR04.startPing() to start a sample cycle **/
    void init( uint8_t trigpin, uint8_t pingpin );

    /** Start a sensor ping cycle
     **  turns on TRIGPIN and enables interrupts
     ** Presumes that SR04init() initTimer2() have already been called.  **/
    void startPing(void);

    /** return true if there is a new distance value available
     **  will clear itself, so a second call will return false...  **/
    bool available(void);

    /** return the last distance value from the sensor
     **  if it's 0x0000 we didn't get anything...  **/
    int16_t getDistance(void);

After the class is initialized, a call to startPing() will send a trigger pulse and wait patiently for the results. Under the covers, the Trigger output pin is set high and Timer 2 is started, a count interrupt is fired after two counts and used to turn off the Trigger pin, thus starting the Ping cycle. When, and if, the timer wraps around on 256 64uS counts (~16.4mS), the overflow interrupt fires and a global status variable is incremented -- this allows for an extended count range, in this case up to 4 bits or x16. When the Echo input pin goes low, the input pin interrupt fires, all the counts are counted up, and the available() interface will signal by returning true -- just once. When that happens getDistance() can return something useful.

Results

The speced range of good distance data is from about 10 to 360 (in 64uS increments). I did not subtract the two-four initial trigger counts so you can do that if you want a bit more accurate close range measurement.  If you multiply the count value by 1.1 you can get fairly close to the actual distance in CM.

However in a spot check, I did not get reliable distance counts beyond about 180, i.e. 200cm, so YMMV. Also it jumps around, failing for a number of cycles before coughing up an occasional good value.

A note on the bad values.... If there is no ping return received the sensor just keeps going until it gets tired. The spec says this should be 38mS after the trigger, but the reality seems to be closer to 150mS. So when there is nothing to sense, the time between cycles is quite long. When the ping goes missing, available() will eventually return true and the getDistance() method will return 0 -- this just makes it easier to see on a data plot. Should everything fail -- the counter will just keep counting up to it's 16x maximum and getDistance() will return 0x8000 (a negative number).

For a usage example look to the test.ino file. Connect the sensor to Gnd and +5v power, Trigger to Pin 2, and the Ping to Pin 3. Create a global HCSR04 object and call init(pinT, pinP) in setup(). Then call startPing(), available() in a loop, and getDistance() when available returns true.

So simple. Even I could do it!