Month: May 2012

LabVIEW is awful

This is really just a rant, I’ll have neat and useful information in my next post, I swear.

Everything that this guy lists that I have had the displeasure to run into is correct, and worse than he makes it sound.

LabView is a graphical environment for creating processes to manage a flow of data, usually acquiring it from some device, performing some processing on it, and displaying or recording the data. To create a process in LabView, you drag and drop little boxes which do things to the data, and then point and click to draw wires between the boxes, which show how the data should flow. This is kind of a problem, for a number of reasons.

Imagine if you are trying to get the 1st through the 50th elements of an array. Near as I can tell, in LabView, you use an “Index Array” block, wired to fifty integer constant blocks (each containing a digit in 0..49) with 50 wires. The “Array Subset” block sounds promising, but actually gets you an array, not the elements. If you want to expand this to, say, 100 elements, you need to add 50 more constants, and 50 more wires. This gets tedious very fast, but I guess it’s not so bad, if you otherwise can’t program, and so don’t know that real programming languages will just let you operate on members of an array without pulling them out first, using syntax that takes more time to describe than it does to type.

See, if I wanted to get the fifth element of an array of integers in LabVIEW, multiply it by 10, and put it back, I’d have to use an “Index Array” block, an “Integer Constant” block with the value 4 (zero-based array indexing) to get the value, a “Multiply” block and an “Integer Constant” block with the value 12 to do the multiplication, and a “Replace Array Subset” block using the first “Integer Constant” block to put the value back. This would also require at least 8 wires. I would have to put all of those things in place, and then wire them up using the mouse.

Or I could type “arrayName[4] = arrayName[4] * 10;”, assuming I was working in C, C++, or Java. For Python and Perl, leave off the semicolon. Oh hey. See what I did there? The same operation, only mine is good for 5 languages, takes around 33 characters (so seconds to type), and is all done without a single mouse click or paying thousands of dollars for a license. If that were the only problem with LabVIEW, it would be enough to exclude it from me ever considering using it for anything. Since I don’t get to make that choice at work, I just spent the better part of three days trying to get it to format some data and send that data over the network. For those playing along at home, slinging some data across the network is maybe a 20 minute “problem” in any other language that real humans use (brainfuck, befunge, etc. don’t count, and assembly is a corner case).

The miserable interface doesn’t just make it slow to create anything in LabVIEW. It also makes it easy to get wrong in annoying ways. The analog of a typo in Labview is connecting things wrong. Given that you are aiming for a ~10 pixel target with no space between it and and the equally connectable, but incorrect, targets on either side of it, the quality of your code depends on the resolution of your mouse and your visual acuity. That’s right. Not your ability to break down a problem into its component parts and determine what algorithms solve those parts. Your mousing skills are what determines if you got your “code” right. This also means that if you are hooking up 60 connections, and you accidentally skip one, you have to move a bunch of the other connections to get the one that you skipped back into place. God help you if you don’t catch it, as the data will be ok, but one element of it will be out of order.

My new favorite way of commenting out code blocks

/* Debugging, print out the array
for (int ii = 0; ii < sizeof(data); ii++) {
  if ((ii % 8) == 0) {
    cout << endl;
  printf("%02X ", ((unsigned char *) data)[ii]);
cout << endl;

That last line is a single line comment that closes a multi-line comment. By adding or removing "*/" to the comment that describes the block, I can comment out the entire block. No more hunting for the proper point to close it at, just adding or removing the comment closure to the top line.

Of course, this doesn't work if there's a multi-line comment inside the code block.


I’m trying to build a tricycle tallbike, because nothing says “overconfidence” like having your first welding project be something that drops you into traffic if the welds break.

It will have two front wheels and one rear wheel. The rear wheel will provide power, and the two front wheels will provide steering. I’ll post photos as soon as I have any of it together.

Low Power Electronics

I am building a set of strings of lights to illuminate a labyrinth. As someone walks the labyrinth, the strings of lights will light up ahead of them to show the way, and fade out behind them as they pass. Instead of doing the build from the ground up, I’m starting with solar-powered garden lights that charge during the day, and light a string of lights at night.

My initial thought was that this would be a pretty simple task. I’d rig each light with a Sharp IR ranger, poll the ranger, and light the lights when something got close enough. Once it passed, I’d set a timer based on how long it takes to walk a strand of lights, and then shut the lights off when the timer timed out.

Unfortunately, that idea went away when I got the solar light. The light uses a single 1.2V battery, and runs the LED strand by having a simple boost converter double that to pulses of around 2.5V at a high enough rate that the LEDs don’t look like they are pulsing. I figured I would get around that by rectifying the pulses using a voltage doubler, which would get me 5V for my microcontroller and sensor. Unfortunately, voltage doublers get you voltage at the expense of current. The Sharp IR rangers can eat around 20mA, and the microcontroller is another 15mA or so. With that amount of load, the voltage on the voltage doubler rapidly falls back to ~2V. The Sharp IR rangers don’t work at anything less than about 4 volts, so I couldn’t use them.

I decided that since I don’t need range measurement, just the presence or absence of something in the range of the detector, I could get by with lighting the area up with 38kHz modulated IR, and picking it up with an IR detector module like the ones used in TVs to receive the remote signal. The microcontroller can generate the modulation signal to drive the IR LED. I got the code to do it here, I think, but that site is down now. In practice, this works just fine. I used my Arduino to do a quick sketch of the detection circuitry, and got it to blink an LED.

Unfortunately, the IR detectors I have also don’t work with less than 5V. However, unlike the Sharp IR rangers, there are a bunch of manufacturers that make the TV remote receivers, and some of them operate down to 2.4V. I ordered some of these, and set up my microcontroller, IR LED, and remote receiver so I could blink an LED by sending a IR pulse.

That worked just fine on battery power, but running from the voltage doubler still drained the caps too fast. Powering the IR LED at reasonable brightness just took too much current. In order to let the capacitors in the voltage doubler recharge, I shortened the IR LED on time to a 10th of a second, and put the microcontroller in a very low power (i.e. it runs on microamps, rather than milliamps) sleep mode when it was not firing the LED. Since the circuit spends most of its time off, the IR detector is the main draw on the voltage doubler. So far, this seems to work. If I want to save even more power, I can power the IR detector from a pin of the microcontroller, and shut it down when the microcontroller goes down.

Soon, I’m going to test the full circuit. I’ll post about it if I have to make any wild and crazy hardware changes.

Conductive tape for biosignal acquisition

If you want to monitor electroencephalographic (EEG, electrical signals from the brain) or electromyographic (EMG, the electrical signals from moving muscles), you need to use electrodes to get the signal. The electrodes are generally not reusable and are kind of expensive. They usually run somewhere from $0.70 to $3.00 each, although the 3M Red Dot electrodes are much cheaper. The electrodes usually use a conductive gel surrounded by a ring of non-conductive adhesive, which makes them large and difficult to put close together.

It seems likely to me that you could use electrically conductive tape to improvise contacts of any size and shape. The adhesive probably isn’t tested for use on humans, and the conductive element is sometimes something that people have an allergy to, like nickel or silver, but it could be sufficient for self-experimentation for quick hacks. It would also be an order of magnitude cheaper

Conductive tape:
Cheapo Red Dots: