Saturday, June 27, 2015

Sonar Development: Towards Something That Works In Water

Bathymetric survey data from a NOAA ship.

After a few months of distractions to prepare for a new kid, build a quadcopter, and work a bunch, I'm trying to get my sonar project moving forward. As documented in previous articles, I've got a simple digital sonar working in air. It was a simple way to test the echo detection algorithms. I'm convinced if I can figure out a way to use piezo transducers to transmit sound in the water, I can make it work.

Previous installments:

Audible Frequency Chirp Sonar on the Stellaris Launchpad

Initial Experiments - Sonar in air with a conferencing speaker mic and Python

So the next challenge is how to mount the piezo element and efficiently couple the sound to the surrounding water. One way to do this appears to be to pot the transducer in a potting compound that closely matches the density of water.

This article from NOAA on building hydrophones for listening to whales details one way to pot a transducer, and also includes a high gain amplifier circuit. My current plan is to build one, and figure out how to get the ADC on the Launchpad reading the audio. From there, I can make a transmit circuit. The challenges will likely be in acoustic coupling, transducer selection, and getting enough power into the water to travel a reasonable distance.

I considered using piezo disks, but I found that getting any sort of output from them at all requires them being mounted at either their edges or nodal points in a resonant cavity known as a Helmholtz chamber. I don't think I can manufacture one to the precision needed for the small size. I'm going to work first with cylindrical piezo units as used in the hydrophone above.

I intend to try one with a resonant frequency in the audible range - that's not going to result in very good resolution, but should be easier to debug since I can hear it and use PC audio equipment to measure it. Once that works, I'll switch to higher frequencies.

The next step is to build a functioning hydrophone with a piezo element, get it working with the op-amp, and get that feeding into the ADC of the Launchpad. That will complete the receiver side, and test the methods of acoustically coupling the transducer to the water.

Sunday, June 14, 2015

F450 Quadcopter Mods: Walkera G-2D Gimbal and XIaomi Yi Camera

I built my F450 with aerial video in mind. Once I got it flying, it was time to select a camera and gimbal. 

The camera needs to be able to record at high framerates to reduce the "jello" effect of rolling shutter. If you try to strap a cheap keychain camera to the frame of your quad, it is very likely that the result will be a garbled mess of distortion. This is because the CMOS sensors in those cameras scan each frame into memory over a small period of time. Vibration causes the frame to move as it is being captured. 

Additionally, even if you get the vibration under control, the rapid movements in all directions as the quad flies around will make you ill. It's not a lot of fun to watch. 

The solution is a camera that can record at 60 fps and a motorized gimbal to compensate for the motion of the quadcopter and keep the camera level. There are gimbals that use servo motors, but the best use brushless motors, which are quiet and smooth. They nearly instantly compensate for the motion in pitch and roll that occurs from pilot inputs and wind gusts.

I selected the Xiaomi Yi camera. This has the same imaging sensor as a GoPro without some of the frills, and is much less expensive. They are currently available on Amazon Prime for $88. The don't come with a case, or even a lens cap. The Android version of the app is rather untrustworthy looking - it is currently distributed off of a file sharing site I normally associate with pirated software, rather than from the company's website. "Here! Run this random APK from the Internet on your phone! It will be fine!"

Yeah. I dug out an old phone that doesn't have access to any of my important stuff and used that. I used the app to set up the video mode (60 fps at 1080p) and timelapse mode (still frame every 3 seconds). You can toggle between these modes with the camera's button - you really only need the app once.

I also ordered a Walkera G-2D 2-axis gimbal. This only compensates for pitch and roll, but uncommanded yaw motions don't seem to be much of a problem. I am extremely pleased with this gimbal for the money. It has an onboard regulator, so you can run it straight off your 3S lipo pack. I connected it to my main power line on the quad and it fired right up. It supports the use of auxilliary channels on your receiver to aim it in roll and/or pitch, but it doesn't require it - you can set the tilt and roll angle with a couple of trim pots and leave it alone, and it requires no connection to your receiver. It even comes with a small tool to adjust the pots with and the needed Allen keys. It worked right out of the box, and bolted directly onto the lower frame of the F450, aligning nicely with the slots on the lower frame. I secured it with 4 bolts.

One note: the gimbal is not designed for the Xiaomi Yi and the existing mount doesn't fit. I found that the frame could easily be removed, a 1/4" cardboard shim cut to level off the mounting plate, and a large zip tie easily secures the camera to the gimbal. There is probably a more dignified way, but that works just fine.

I am really pleased with this combo. I am still seeing some vibration in the video that I want to eliminate, but it's by far the best video I've gotten from an RC model so far. More to come on the vibration problem as I work it out. (Update on how to fix this below)

Here are a couple of still frames of a local park, shot in timelapse mode.

And some video....

Video Test Flight 3 - Xiaomi Yi and Walkera G-2D Gimbal on F450 from Jason Bowling on Vimeo.

Update on the vibration problem, and a note about the camera:

1) The vibration was improved by changing the vibration dampeners that came with the gimbal with more rigid ones from HobbyKing. The dampeners that it comes with are too soft.

2) Additional improvements were made by inserting soft foam earplugs into all four vibration dampeners.

3) The lens rectification function on the Xiaomi Yi makes the edges of the video very blurry. Once I fixed the vibration, the edges were still bad. I turned the lens rectification off, and it's much better. Here's a test flight with these improvements.

TestFlightNoFisheyeCompensation from Jason Bowling on Vimeo.

Saturday, June 6, 2015

F450 Quadcopter Build and Flight Testing

This is my F450 quadcopter. There are many like it, but this one is mine.

I have a lot of experience with RC airplanes, but I'm new to quadcopters, so I want to document the build in case it is useful to others. I learned on the excellent and incredibly affordable Syma X1, which is serious fun for the money and a perfect trainer when flying indoors. I put a number of flights on an ARDrone, until it went berzerk and parked itself in a very tall tree. At that point. I decided something with a real, proper RC system was in order.

A few abbreviations:

ESC - electronic speed control. Converts control inputs from you (through the flight controller) into a throttle output to one of the motors.

FC - Flight controller - a small microprocessor board with gyros and accelerometers that stabilize your quadcopter in flight. It handles the mechanics of keeping the machine in the air by making small adjustments to the motor power many times a second, and turns your stick input into your desired motion.

BEC - battery eliminator circuit. Steps down the main flight pack's 12.6 volts to the 5V the receiver and flight controller needs. A regulator.

3S - a 3 cell lithium polymer battery.

Here's what I selected for parts:

A combo containing the frame, motors, ESCs, and propellors. 

This contained:

1 x F450 frame kit
1 x F450 Landing gear( 4pcs/set)
4 x Sunnysky X2212 980KV Brushless motor
4 x HP SimonK 30A Speed Controller
2 x 1045(CW+CCW) Black Propeller
2 x 1045(CW+CCW) Red Propeller

Knowing what I do now, I'd not have bought this as a kit. I would have bought the components individually. More on that later - live and learn.

KK2.1 Flight Controller (FC)

FlySky FS-T6 radio system

Turnigy 2200 mah 3S Lipo pack

That covered the obvious stuff. Then as I examined the kit I determined I needed some less obvious stuff.

Heavy silicone wire to connect the quad's power distribution to the battery

XT60 connectors. You need at least one on the end of those nice wires you just bought. The other end gets soldered to the power input on the frame's power distribution system.

A set of 5 male to male JR style servo connectors. These go between the flight controller and the receiver outputs.

A 5V switching regulator, because I don't trust the linear regulators on the ESCs.

A dedicated low voltage alarm. I never got the low voltage cutoff on the flight controller to work right. This one works great. You need one or the other, since quadcopter ESCs don't have a low voltage cutoff like airplanes do. Set to 10.8V, you have 30-60 seconds to get it on the ground before you lose power.

A pack of 3S balancing wires, to connect the battery to the low voltage alarm.

Whew. OK. Once you have the stuff, building it is actually quite easy. You need a higher power soldering tool - I used a soldering gun - since you need to solder heavy wires to the copper traces on the frame. There is an extremely helpful build video from Legend RC here:

Other very useful links if you are new to quadcopters:

Identifying the props and their locations

Connectors and Plugs for Quadcopter Newbies

A great guide to quadcopter wiring. This goes over how to connect the various boards.

Be sure to read the KK2.1 manual section on powering the board carefully. I chose to cut the red wire from all 4 ESCs that connects to the FC motor outputs and power it with a dedicated switching Battery Eliminator Circuit (BEC). The switching regulator runs cooler and more efficiently that the linear regulators on the ESCs.

One of my ESCs was dead on arrival. I didn't find it until the kit was 90% built. I couldn't return the whole kit, and even returning the dead ESC to China would have a been a serious pain. I tracked down the same part on Amazon and bought a replacement, along with a spare. This is a serious drawback to buying the kit.

After very carefully checking propellor rotation direction, as well as making sure the correct prop was on the correct motor, I did a quick test flight, and was surprised to find that it flew fine with stock settings on the KK 2.1. I did make some PID adjustments, but it was quite controllable. 

There were bugs to work out. My KK 2.1's low voltage alarm, set to 10.8V, would howl continuously in flight, and cease on landing. I never figured out why. I turned it off and installed a dedicated low voltage alarm, listed above, and it works superbly. 

On the first few flights, I have trouble with split second instances where the motors would just STOP. All at once, for a fraction of a second. It would fall abruptly, and then recover, unless I happened to be low. I first blamed the linear regulator on my BEC.I tested with a dedicated receiver pack, did a quick test flight, and presto, it was fixed. Victory! I installed a nice dedicated switching BEC, went flying, and SMACK, it fell out of the sky again. It finally dawned on me to range test it. On the ground, with the motors spinning just above idle, I started walking backwards. At 40 feet or so, the receiver light blinked out. A few steps forward, it came back on.

Argh. Radio trouble. Gambled. Ordered new receiver. Got lucky - that fixed the problem. No way to return cheap dead receiver, at least not economically, so into the trash it went and I ate the $15. But it passed a range test and works fine farther than I can see the quadcopter.

ALWAYS RANGE CHECK YOUR MODELS. I have known this for years, and got lazy, and it bit me.

Several more flights, and a new problem cropped up. Propellor blades started randomly separating from the hubs. Once in flight, causing a crash from 30 feet, and once on takeoff, narrowly missing me. Cheap plastic props that came with the kit are absolute garbage - to the point that they are dangerous. Into the trash they went. Ordered some 10x4.5 carbon fiber props, which are absolutely superb. My flight time immediately improved from 7 minutes to 9. I'm not sure if they would fail before the bones in my finger would, so... respect. 

One final note about propellors - they aren't perfectly balanced from the factory. Take the time to balance them - mine flew much more smoothly and quietly than before they were balanced. My video quality dramatically improved too, since it eliminated the jello/rolling shutter artifacts I was getting.

I borrowed a friend's Dubro prop balancer and used scotch tape on the back of the blades to balance them. Went surprisingly quickly. I intend to buy a balancer and add it to the periodic maintenance list. I never bothered with planes, but it matters a lot for multicopters.

I now have perhaps two dozen flights, and the bugs are worked out. It is a reliable machine, climbs well, and has plenty of lifting power. I printed a camera mount for an ancient Canon point and shoot camera and it hauled it around just fine - all 1/2 lb of it. I have since upgraded camera and added a gimbal - more on that soon.

Knowing what I know now, I would not have bought the kit - I would have bought the same components, with decent propellors. That way, if I got a bad speed control, I could return it, rather than the entire kit.  Other than that, I am pretty pleased with it. 

Saturday, February 21, 2015

GT2 Belt Drive Conversion of Printrbot Simple (Wood late 2013 model)

One of the defining characteristics of the 2013/early 2014 versions of the Printrbot Simple was the use of Kevlar fishing line for the motion transfer on the X/Y axis. A rubber hose gets superglued to the stepper shaft, a Dremel sanding wheel gets glued to that, and the fishing line gets several wraps around it. It kept cost down (the original was just shy of $300 in kit form) and it works surprisingly well. Mine has held up for quite a lot of printing over the 13 months I have had it running.

However, it did have a couple of disadvantages. It required tightening every now and then. It can result in a loss of precision, because the fishing line can walk back and forth on the drum. And frankly - it's just not very dignified looking. Here is a view of the X axis drive with the bed removed.

Thanks to the work of Thingiverse contributor iamjonlawrence there is a printable conversion to GT2 belts for both the X and Y axis. Newer Simple models come with belts, though they cost more than the original Simple kit did.

Y axis
X axis

Jon is a mechanical engineer, and it shows in his hobby work. He has released a number of upgrades for various versions of the Printrbot Simple, and it is accompanied by professional drawings and detailed bills of material. The parts in these kits were very well thought out and fit perfectly, I highly recommend his work.

I printed two sets of the parts - I was concerned that I would have my printer torn apart, and if I messed up a part I would not be able to print replacements. This turned out to not be necessary, but I still think it is worth doing.

I made sure my printer was calibrated well before printing the parts. The tolerances are snug, but if your printer is printing accurately it will fit with only minor brushes with a file to remove burrs or other loose material from the print.

In addition to the McMaster Carr part numbers called out on Jon's BOM, I used the following components from Amazon:

808 Bearings
Belts and pulleys (there is plenty of belt for this conversion - I had enough left over to replace one of the belts if I ever need to)

Note that FLDM printers tend to print holes and slots slightly small. I calibrated mine to accurately print outside dimensions, and just drill my holes to the right size. With the hardware specified on the BOM, a 7/64 bit will make the hole sized nicely for the screw to thread into. A 1/8" bit will allow the screw to pass through smoothly.

You'll need to recalibrate the X and Y axis since the pulleys are slightly larger than the original drums.

Also, have extra zip ties handy, you'll need them to put things back together.

Procedure - Y Axis

First, I clipped the zip ties holding the Y axis carriage to the motion rods. I then removed the stepper.

Next, I installed the new motor plate and bearings, and aligned the pulley.

I fed the belt in and checked motion, and secured one end of the belt to the stop.

The stop gets belted on.

The second stop gets attached. 

Securing the belt to the tension block is a little tricky. I had to remove material from the slot that the belt passes through to let it pass through twice. The drawing shows clearly that the belt should just fit through the slot when folded back on itself. A short length of filament acts as a pin to hold the filament in place. There are detailed shots of this in the X axis section.

Tension is adjusted by turning the screws in the tension block. At this point, I connected to the printer and tested the motion. All looked good, so I moved on to the X axis.

Procedure - X Axis

The X axis is more involved because you have to install a replacement motor mount plate for the X axis stepper. This is not a trivial process, but it went pretty smoothly.

First, the bed is removed and the X carriage is removed by clipping the zip ties holding it in place.

The side opposite the control board is removed.

The bottom plate can now be pulled free and the X axis motor mount is removed.

The new bearing plate is assembled.

Carefully align the pulley with the bearings. They are a snug fit, but they do fit, and don't allow any slop when assembled.

Install the new motor plate and reassemble.

The new belt ends are held in place with the zip ties securing the carriage to the motion rods. As the drawings call out, the carriage is flipped over and a new hole drilled for the X axis end stop screw.

Here is a detail shot of how the belt tension blocks work. I had to open the slots a bit with an exacto knife, just enough to pass the belt when it is folded back on itself.

Test it! I had to remove a little material from the carriage to get it to run smoothly, just rounding over an edge.

I had to modify my back clips that hold my heated bed on. I just bent and cut office clips into a z-shape. Details on the heated bed installation is here.

Initial test prints look really good. I am in the processing of recalibrating the X and Y motion in the Printrboard, since the pulleys are slightly larger than the original sanding drums. I will post the final values once they are determined.

Update: X and Y values for M92 are both just a hair above 80. I have mine printing to within .001" on a 2.000 inch square test model.

In Repetier Host, the GCode commands can be entered into the GCode command box on the manual tab, shown below. Enter the command you want to run and hit the Send button.

A good overview of the math is available on this excellent blog entry by Zheng3.

Sunday, January 18, 2015

Audible Frequency Chirp Sonar with the Stellaris Launchpad

Over the last year I've been working towards an underwater sonar system for ROVs and surface boats. In order to learn the basic signal processing required to detect the echoes, I initially got a simple sonar working in air with a desktop conferencing USB speaker/mic running on Windows. A writeup, including source, is here. That article describes the algorithms used in detail and would be a good read if you want the details of how this works.

The next logical step seemed to be to get it working on a microcontroller. There are plenty of low cost ultrasonic sonar modules available that work really well in air, but the idea was to work towards getting a sonar that worked in water. There are currently no low cost sonar modules for hobby use in water. Additionally, the low cost modules only give one echo - with a signal processing approach like this, you get a series of echoes that may convey more information about the environment. As an example, a boat floating above a school of fish could detect both the fish and the bottom.

I selected a Stellaris Launchpad because of the high speed analog to digital converters (ADC) and the 32 Kof RAM. At the required sample rates, the Launchpad has just enough RAM to send a chirp, and then record a fraction of a second of audio so that the echoes can be determined. Higher frequency sound will require a higher sampling rate, so I may need to switch to a Teensy 3.1, which has 64K of RAM.

A chirp waveform is computed and sent to a small piezo speaker driven by a simple transistor circuit. The piezo supply voltage (VCC in the diagram below) is provided by 3 nine-volt batteries in series to obtain 27V. This diagram shows how it is connected. This is not my diagram - I found it online, but I don't have a reference. If this is yours, please drop me a line.

The return echo is detected by a small amplified microphone from Adafruit. I like this module because it has an integrated level shift. Rather that swinging from -V to +V, it is shifted to 0 to +3.3V so that it can be connected to an ADC. It's very convenient.

A couple 3D printed parts hold it all to the board just to keep it pointed in the right direction.

The chirp is sent, and the audio immediately starts recording to catch the echo. The same correlation function as used in the previous article is used to pull the echoes out of the recorded audio. The intensities of the correlation function are sent through the debug port to the PC so that it can be plotted. 

I need to work on optimizing the echo detection code - currently it works on the audio from each pulse for 4 seconds or so. Also, the power output of the audio transducer is very low, so range is pretty limited. It has an effective range of between 3-9 feet. Closer than 3 feet, the echo is hard to pick out of the noise produced when the pulse is sent.

As in the original experiments with the speaker/mic, the results are plotted with a simple Python program set up similarly to a fishfinder display. The results of a test run are shown below. Source for the Python display is modified from code from the previous article. 

Source code for the Launchpad is given below.

Next steps are to work on getting transducers working under water and increasing transmit power. I've made a simple hydrophone to test transducers with - update coming soon.

Audible Frequency Chirp Sonar with the Stellaris Launchpad from Jason Bowling on Vimeo.

#include "inc/hw_ints.h"
#include "inc/hw_memmap.h"
#include "inc/hw_types.h"
#include "driverlib/sysctl.h"
#include "driverlib/interrupt.h"
#include "driverlib/gpio.h"
#include "driverlib/timer.h"
#include "driverlib/debug.h"
#include "driverlib/fpu.h"
#include "driverlib/pin_map.h"
#include "driverlib/rom.h"
#include "utils/uartstdio.h"
#include "driverlib/adc.h"
#include "inc/hw_timer.h"
#include "inc/hw_ints.h"

#define numSamples 6000 //size of receive buffer
#define sampleRate 80000 //sample rate at which the audio for sending and receiving is performed
#define pulseLength .0015  //transmitted pulse duration in seconds

#define chirpStartFreq 5000  //in Hz
#define chirpEndFreq 8000  //in Hz

int chirpLength = 0;

 unsigned long g_sampleCounter = 0;
 unsigned long ulADC0_Value[1];
 unsigned long rxBuffer[numSamples];
 int pulse[900]; //stores waveform for sending and comparison. Only need integers for square wave. Could do with bits to save memory
// must be at least pulseLength * sampleRate

 //double output[501];

void initConsole()
  // Initialize the UART at 115200.
     //ROM_GPIOPinTypeUART(9600, GPIO_PIN_0 | GPIO_PIN_1);
     UARTprintf("\nConsole Initialized. System clock is %4d\n", SysCtlClockGet());


void initADC()
   // The ADC0 peripheral must be enabled for use.

         // For this example ADC0 is used with AIN0 on port E7.


         // Select the analog ADC function for these pins.


         // Enable sample sequence 3 with a processor signal trigger.  Sequence 3
         // will do a single sample when the processor sends a signal to start the
         // conversion.
         ADCSequenceConfigure(ADC0_BASE, 3, ADC_TRIGGER_PROCESSOR, 0);

         // Configure step 0 on sequence 3.  Sample channel 0 (ADC_CTL_CH0) in
         // single-ended mode (default) and configure the interrupt flag
         // (ADC_CTL_IE) to be set when the sample is done.  Tell the ADC logic
         // that this is the last conversion on sequence 3 (ADC_CTL_END).  Sequence
         // 3 has only one programmable step.

         ADCSequenceStepConfigure(ADC0_BASE, 3, 0, ADC_CTL_CH0 | ADC_CTL_IE |

         // Since sample sequence 3 is now configured, it must be enabled.
         ADCSequenceEnable(ADC0_BASE, 3);

         // Clear the interrupt status flag.  This is done to make sure the
         // interrupt flag is cleared before we sample.
         ADCIntClear(ADC0_BASE, 3);


 //configure 32 bit periodic timer
  TimerConfigure(TIMER0_BASE, TIMER_CFG_32_BIT_PER);

void startTimer()
 unsigned long ulPeriod;

 //set timer rate
   ulPeriod = (SysCtlClockGet()/(sampleRate*3));
   TimerLoadSet(TIMER0_BASE, TIMER_A, ulPeriod -1);

   TimerEnable(TIMER0_BASE, TIMER_A);

void stopTimer()

         // Disable the Timer0A interrupt.

         // Turn off Timer0A interrupt.
         TimerIntDisable(TIMER0_BASE, TIMER_TIMA_TIMEOUT);

         // Clear any pending interrupt flag.
         TimerIntClear(TIMER0_BASE, TIMER_TIMA_TIMEOUT);

void initLED()
 //enable GPIO pins for LED

void initPiezo()
 //enable GPIO pins for piezo

void generateChirpWaveform()
unsigned long int freq = chirpStartFreq;
int value = 1;
unsigned long int start = 0;
unsigned long int stop = 0;
unsigned long int counter = 0;
int count = 0; //temp
int sampleComplete = 0;

//step through array from 0 to 1/2*freq, setting value. Invert value. Proceed to 1/2*freq, setting value. Calculate new freq. Repeat.
//values stored in pulse[]

while (!sampleComplete)

stop = (int) start + ((1.00 / (freq * 2.00)) * sampleRate);

for (counter = start; counter < stop; counter ++)
 {//check position and set sampleComplete when at end of chirp
 if (counter < pulseLength * sampleRate)
  pulse[counter] = value;
  sampleComplete = 1;
//invert waveform value to be set for next half of cycle
if (value == 1)
 value = 0;
 value = 1;

//calculate new freq based on position in pulse. Ratio of stop/chirpLength vs freq increment / chirpEndFreq
freq = chirpStartFreq + (((chirpEndFreq- chirpStartFreq) * stop)/(pulseLength * sampleRate));

//position for writing next half cycle
start = stop;
chirpLength += 1;
} //end while


void playChirp()
long int count = 0;
long int endSample;

endSample = sampleRate * pulseLength;

 while (count < endSample)
  if (pulse[count])

  SysCtlDelay((SysCtlClockGet() / (sampleRate * 3)));
  count ++;


void ftoa(float f,char *buf)
 //code from
 int pos=0,ix,dp,num;
    if (f<0 data-blogger-escaped-buf="" data-blogger-escaped-dp="0;" data-blogger-escaped-f="" data-blogger-escaped-pos="" data-blogger-escaped-while="">=10.0)
    for (ix=1;ix<8 data-blogger-escaped-f="f-num;" data-blogger-escaped-if="" data-blogger-escaped-ix="" data-blogger-escaped-num="">9)
            if (dp==0) buf[pos++]='.';
buf[pos - 1] = '\0';

void processSample()
int a = 0;
int bufferStartPosition = 0;

double normalizedSample = 0.0;
double windowSum = 0.00; //cumulative sum for this window
double temp = 0.0;

char buffer[20] , *str;
str = buffer;

//audio values in rxBuffer are shifted integers. Normalized audio is -1 to 1. Recorded samples are 0 to 4096
//Divide by 4096 and subtract .5 to shift to this range.

//stored pulse is stored 0 to 1. Multiply by 2 and subtract 1 to normalize.

while (bufferStartPosition < ( numSamples - chirpLength))
for (a = 0; a < chirpLength; a++)

 normalizedSample = (rxBuffer[bufferStartPosition + a]/4096.0) - .5;
 //temp = normalizedSample * ((pulse[a] * 1.00));
 temp = normalizedSample * ((pulse[a] * 2.00) - 1.00);
 windowSum = windowSum + (normalizedSample * temp);


bufferStartPosition += 1; //increment bufferStartPosition to move window
windowSum = 0.00;
//end outer loop


int main(void)
//initialization complete

 int pingCount = 0;

 while(pingCount < 1000)
  //record audio
  pingCount = pingCount + 1;

 while (1) {}


void Timer0IntHandler(void)
 // Clear the timer interrupt

 // Trigger the ADC conversion, Wait for conversion to be completed.
 ADCProcessorTrigger(ADC0_BASE, 3);

 //everything after this can be moved out of the ISR
 //set a flag and poll for it in main()
 while(!ADCIntStatus(ADC0_BASE, 3, false))

 //take an ADC reading
 ADCIntClear(ADC0_BASE, 3);
 ADCSequenceDataGet(ADC0_BASE, 3, ulADC0_Value);

 if (g_sampleCounter < numSamples)
  rxBuffer[g_sampleCounter] = ulADC0_Value[0];
  g_sampleCounter = 0;



Saturday, December 27, 2014

Pebble Smartwatch Review

I toyed with buying a Pebble for several months before I actually pulled the trigger. I bought it to solve a specific problem, and then discovered it solved some other problems I had not actively been working on a solution for. It also has a few drawbacks. Here's what I've learned after using it for a couple months.

I keep my phone silenced at work, so that it does not interrupt meetings. However, I sometime miss the silent alerts - I just don't feel the vibration when a call or text comes in. Pretty much the only people who call or text me during the work day are family, and if they do, they need to reach me. Even when I do feel the alert, I consider it bad form to fish my phone out of my pocket to see what it is - it's not very polite at best, and can give the impression you are ignoring a boss or customer at worst.

I knew the Pebble could alert me to incoming texts and phone calls. That, alone, was worth the gamble. The price dropped to $99 after the Android Wear watches came out, and I decided it was time to give it a shot. I spoke with a couple people who had the Android Wear watches, and although they are impressive technology, I was put off by the high price and very short battery life. A coworker indicated they don't even last a full day, and I didn't want that. So I bought the standard Pebble.

The good...

  • The battery life is outstanding. It will run for an entire week, the way I use it.
  • The alerting works very well. The watch vibrates against your wrist and it's hard to miss. It's quiet and subtle.
  • You can configure which alerts you want. I have mine set to only alert on texts and phone calls, but not things like Facebook notifications. That way, if my phone buzzes but the watch does not, I know it can be ignored until a convenient time.
  • It's waterproof.
  • The application on the phone is a convenient way to load apps and watch faces. 

The not so good...

  • The display driver appears to have some bugs. Sometimes it will start to have distortion or speckles across the display that range from annoying to completely obscuring the content. A restart normally fixes it and it doesn't come back for a while. UPDATE: This is a known hardware issue, caused by intermittent connection between the LCD and mainboard. A search on "pebble screen tearing" brings up lots of results that indicate the fix is to contact support and RMA the watch. I intend to do this.

  • The display darkens significantly in cold air, less than 30 deg F. 
  • The stock wrist band on the low end version is made of some sort of rubber, and it is clammy against the skin if it gets damp. It can easily be replaced, but it stands out against the rest of the device.
  • The pedometer function is wildly optimistic. If I zero it and then hop in the car and drive for 45 minutes, I will have logged 2000 steps by the time I get out of the car. I compared it to an actual pedometer and it was about 50% high by the end of the day.
  • Instead of pulling out your phone, which makes you appear distracted, you now tend to glance at your watch, giving the impression you are in a hurry.

The completely unexpectedly useful....

  • Having a silent alarm clock that wakes you by gently pulsing your wrist is extremely handy if you want to wake at a different time than your partner.
  • The app Sleep As Android integrates seamlessly with the Pebble and tracks your sleep by tracking your movements. If you tell it when you need to be up, along with an acceptable time window, it will watch your sleep and nudge you awake when you are in the shallowest part of your sleep cycle. I find I awake more refreshed and alert. 

  • Additionally, I really like being able to see who is calling and texting if I can't easily get to my phone. Examples are cold weather, or with the phone in a dry box while kayaking.
  • The ability to show different data on the watchface, including time zones or weather, is pretty handy.
  • The music playback controls are pretty cool, and work well with Google Music. It does not appear to work with Amazon Music.

It's not as dramatic a change as, say, the laptop or smartphone, but it's inexpensive and handy. I never miss important calls or text any more, and the sleep tracking and data displays are modest time savers. Overall, I am quite pleased with it.  

Saturday, November 22, 2014

Syma X1 Camera Mount

I think the Syma X1 is about the best fun for the money in RC, ever. It's indestructible, flies well indoors or outdoors in calm air, is agile and fun to fly. It costs $30 or so on Amazon. I love it.

I tried a couple different ways of mounting a camera under it. The main challenge with this is to get it securely attached, since there is an oddly shaped battery assembly below the main platform. It has to be very light, since the quad doesn't have a lot of cargo capacity.

 This is the best I've come up with so far - it uses HobbyKing vibration mounts and some 3D printed parts. I printed them in ABS for light weight and a bit of flexibility, and I recommend that if you try it. The printed ring fits snugly around the circular frame that the control board electronics sit on and is attached with a couple zip ties. I had to slightly drill out the two unused screw holes in the circular frame.

I used an older 808 camera, which it lifts fine. There might be light enough FPV gear out there now, I'm not sure. There is still some vibration in the video - I'll probably try a little foam between the camera and platform to see if I can get rid of that. It's a fairly low frequency, since it's not causing "jello" (rolling shutter).

STL files hosted on Thingiverse here