Well, this is somewhat disappointing… I recently acquired a Samsung Series 5 530U3B Ultrabook which is really nice and was going to make my main laptop for on the work on the go. Unfortunately it supplies insufficient power to my USBTinyISP programmer. The effect is that when I try to program ATTiny45, I get this error:

Binary sketch size: 2,752 bytes (of a 4,096 byte maximum)
avrdude: verification error, first mismatch at byte 0x0040
 0x02 != 0x36
avrdude: verification error; content mismatch

The verification fails on random memory addresses. This means that I will need to add an external power supply to my custom programmer or find a USB hub with external power supply. I think that the latter will be the easiest.

A few weeks ago I found this boxed Syma S031G helicopter in a ModelZone store on a special shelf where they are selling broken or otherwise non working gadgets. There were more of those broken helicopters for sale, but they were in a range of £30 and were listed as having RC transmitter problems or other faulty parts. It wouldn’t have made sense buying one without investigating if repairs wouldn’t even cost more than a new heli retailing for £59.99 at the same store (or 30% cheaper on eBay). Mine only had a handwritten sticker “broken” stuck to it and a price of £9.99. A quick inspection through the box didn’t show any signs of significant damage and shop assistant was kind enough to let me open the box and check if it had all parts. Transmitter, charger, heli, instructions and even spare rear propeller was in the box so I decided to take the risk and bough it.

Just to make it clear, this is not one of those tiny helis that fit into your palm, this is a significantly bigger helicopter with a full size radio remote control. Once I unpacked it I noticed that it had actually been flown as the blades showed a bit of wear and damage.

But generally it looked like it was in a very decent condition.

At first I could not get it to start at all, but then I found out that it has a gyroscope so it needs to be placed on a flat surface and left there for a few seconds in order for the gyroscope to calibrate itself. Luckily I was holding it just far enough in my hand and messing with a remote when to my big surprise the motors kicked in and blades started spinning just few centimetres away from my face! That was close, but it was working!

Unfortunately when I put it on the ground and tried to lift it off, it just didn’t have enough power and kept sliding on the floor with the full throttle on instead of going up in the air. Something was not right. Digging through the internet I found out that some of the guys who purchased it had similar problems, but they all ended up returning the item to the seller and getting a replacement. The helicopter is so cheap that nobody actually cares about fixing them and just bin them once they are broken. Well, that wasn’t an option for me :)

In one of those scarce forum posts I found that one of the owners of a similar heli had the same problem and ended up replacing the motors, because they tend to overheat and somehow wear out. I found a pair of motors for a reasonable £6.95 on eBay and decided to take one more risk for the toy and order them. I received the motors today.

It took a while to disassemble it in order to get to the motors to replace them.

I had to remove all lower part of the helicopter and unscrew the bottom blade holder in order to push the gearbox outwards so that I could access the screws for the motors.

I assembled it back again (without any leftover screws!) and now it works! I can feel the power when I’m holding it in my hands with full throttle and it does lift off from the ground at home, but it’s too big to fly indoors. It was already too dark to go outside and fly it so will have to wait for a real test tomorrow. Hopefully I will not crash it during the first flight :)

Heli – £9.99, motors – £6.95, fun fixing it – priceless!

The world is full of free integrated circuit samples, you just need to know where to look for them. Today I got a very nicely packaged batch of samples from Maxim Integrated. All I had to do was ask nicely :)

I filled all relevant information four days ago and today I have 2 x MAX7219CNG and 2 x MAX7221CNG LED display drivers. They retail at about £8 and £13 without shipping so it’s about £42 of free stuff! Will be using them to control 8×8 LED matrices I got a while back from Rapid Online.

Thanks Maxim Integrated!

I bought this Alba FM clock radio a very long time ago at a car boot sale for £2. Seller was selling a bunch of them. It had everything in the box: power supply, cables, various iPod dock plastic bits and even AV cable. Took it home, plugged it in and… it was working, but no audio at all. I could control the iPod, set the clock and etc, but it just did not make any sound. Well, you know… it was just £2 :) So it was left in a cupboard for a very long time until today I decided to take it out and have a look at what’s inside.

It was very easy to disassemble. Just a few Phillips screws, nothing interesting. Inside there was a bunch of boards all connected together.

A few more close-up pictures where you can see that boards have silkscreens which describe the connector pinouts. Nice!

It consist of 4 boards interconnected together into sort of a circle:

1. Amplifier board
2. iPod connector board
3. Tuner board that also acts as button controller
4. Main controller board that has the LCD screen and some Chinese chip with all the “brains”

It was time to start troubleshooting.

I started with testing the audio signal by connecting iPod and following audio path with the oscilloscope up to the amplifier board with TDA2822. A quick check on the sample schematics for the chip

(image source)

I could see that the signal comes to the inputs on pins 6 and 7, but there is no output on pins 1 and 3. Strange… I started suspecting a faulty chip, but then decided to check if the chip is getting power at all. Nope, no power for the chip. I noticed that it’s not powered directly, but actually power comes from the controller board on a wire named POWER-CTL, goes into few transistors and finally to the chip. This means that the amplifier chip is automatically powered down when controller goes into standby.

A few more tests later I noticed that the signal was never sent to the board when I turned the radio on. I found the microcontroller pin that was sending the signal, but it never reached the board. It all pointed to a faulty SMD transistor. Looking at the board I figured out that this was a PNP transistor and just as soon as I soldered another big one in, it started playing tunes from my iPod!

So iPod was playing through the speakers, AUX input too, but switching to radio source silence could only be heard. Checking the board I also noticed that there was a TUNER-CTL signal going from the controller board to the tuner. Tracing it with the oscilloscope I noticed a similar pattern: a signal is switched on the microcontroller, but it does not get to the tuner board. This time it was a 47k SMD resistor causing this. A quick check with a multimeter in the circuit showed no resistance at all. Strange so I took another big 47k resistor and soldered it on top of the SMD resistor and radio started working!

Now it was time to cleanup a bit and solder the components properly. When I removed the SMD resistor it showed the correct 47k resistance. Yeah, I know that I shouldn’t be measuring components in circuit, but sometimes it’s a quick and easy test. It turned out that when I soldered my own 47k resistor on top, the total resistance of the two resistors became 47k / 2 = 23.5k. Funnily, that made the TUNER-CTL signal finally reach the tuner board. Did they make a mistake during the assembly and soldered a too high resistance SMD resistor? Did they even test it before packing up? Yeah, it’s Alba, a brand you probably shouldn’t trust. I removed both 47k resistors, soldered 22k and the radio started working again as it should have.

A quick check just before putting in last screws to make sure that everything still works and my assembly didn’t screw anything up. Great, it’s still working fine! The audio quality is rubbish, but I had more fun fixing it and finally got to experience the benefits of a high quality oscilloscope to troubleshoot faulty electronics. Couldn’t have done it without it.

There are a few different ways how to program ATTiny microcontrollers – lovely little chip with so much potential. I tried programming with Arduino Uno, but the solution was too clumsy with lots of wires connected to the breadboard from Arduino. Then I remembered that I have USBTinyISP and apparently it is one of the best ways to program these chips.

The schematics on how to wire USBTinyISP to ATTiny45 or ATTiny85 I found from Fritzing library.

I wanted a bit more permanent solution so decided to build it on a stripboard.

It might be not the best layout, but I currently have stripboards only this size. The only place where strips need to be cut are in between the IC and connector legs. It was very easy to solder and it works very well! Still some space left for test circuit if I come up with one.

How to set up your IDE to program these chips can be found in the High-Low Tech blog Programming an ATtiny w/ Arduino 1.0.1.

Update: You really really really don’t want to put your chip incorrectly into the DIP socket. I accidentally did it and the just 10s later the chip got extremely hot. Good thing I managed to rescue it and it seems to be working. Lesson learned!

My highly anticipated 3D printer has finally arrived! I bought it from eBay as a fully assembled device, just because I didn’t want to bother assembling it myself or looking for parts to build from scratch. I was hoping it to be plug and play, but it turned out to require a bit more work to get it working.

It was supposed to be fully calibrated, but it wasn’t. My first print turned out to be quite a bit of a mess.

That’s the base of a cube. The hot end was too high. In fact, it was about 4 mm above the heated bed when it was supposed to be just 0.5 mm above. Once I realigned the heated bed, lowered the endstop of the Z axis it started working as it was supposed to and printed a few nice little test cubes.

I’m still not satisfied with the two corners of the cubes, they are supposed to be close to 90 degrees, but they are somehow rounded. Still not sure what the cause of this is. The hollow box didn’t print very well too. I think I will need to add a fan to the print area in order for the plastic to cool down more quickly, otherwise it distorts some very thin edges.

Solid items print rather well. The bigger one is about 2x2x1cm size.

I had enough testing. What’s the point of those small cubes? :) That’s when I decided that I wanted to print something useful like gears for the next printer!

Click here to view the embedded video.

The big one printed out fine, but the small one was a mess. I think that the problem is somewhat software related for the small one, because printer was trying to print as if it wasn’t a solid block with empty space inside.

I still don’t have a clue what I need to set in Pronterface to make it print a fully solid item. Here is the close up shot of the small part.

So it turns out that my printer is good at printing larger designs until I have it sorted out.

Next item on the list of useful things was a case for my Raspberry Pi. I got the design from the Thingiverse. It turned out stunning!

You can see in the pictures below that the printout of small parts was not very good, but the case still snaps well and holds Raspberry Pi in place. I especially love the airflow vents!

It seems that the printer leaves some empty spaces, that’s something to look into and troubleshoot for later. Could be related to issues with printing out those small bits too.

My biggest suspect now is the big extruder gear. It is a bit loose on the bolt and printer does not quite stop the extrusion when printer reverses the extrusion motor.

A few tips if you have just purchased a 3D printer:

• Aligning of all axis and heated bed it is a must. 3D printers are somewhat delicate, they can be easily misaligned during transportation. Test your calibration with this calibration object.
• If you are trying to align endstops and printer does not go beyond the previous position of an endstop, just type in “G92 Z40″ in the Pronterface for RAMPS board with Marlin firmware. This will make the printer assume that Z axis is still 4cm above the endstop.
• Start with very basic objects like cubes and etc. Make sure they are printed correctly before printing any complex objects.
• Be patient and don’t try to remove the object while the heated bed is above 60 degrees Celsius. At 40 degrees it will be very easy to remove.
• Ensure that your 3D item is printable and does not have any parts that “hang in the air” without proper support.

DIY 3D printers may be a lot cheaper than industrial, but require a lot of tinkering and manual calibration. It’s still amazing that you can hold an item in your hands when it was only a 3D design in your computer minutes ago. It’s hard to describe how excited I am when I finally able to experience the potential of 3D printing!

I will keep updating this blog with my adventures in 3D printing and troubleshooting. Make sure you subscribe to my RSS!

I received a few Arduino touch sensors from DealExtreme just because they were dirty cheap and I have a few ideas where I could use them as device power switches. There is probably an easier way to build a touch sensor for Arduino without that many additional components, but let’s see what we can do with this cheap sensor for just $2.6 or less than £1.7.

As for most things from DealExtreme (and many other cheap components sites originating from China) there is no documentation, but it turns out to be very easy to use this sensor. Just hook it up to an Arduino using the following diagram:

It has 4 pins:

• A0 – inverted signal
• G – should be connected to ground
• + – should be connected to 5V power supply
• D0 – touch signal

Touch signal consist of 50Hz signal pulse with 4.8ms pulse width on the D0 output pin for as long as finger (or any other body part) touches the bent pin on the transistor.

The A0 pin produces inverted signal.

That’s all there is to it. The pulse signal provides a small bit of complexity for the Arduino code, but is easily handled by adding a 50ms timeout of HIGH signal in the D0 pin connected to digital pin 3 on Arduino:

//setup default LED on pin 13
const int ledPin =  13;
//setup touch sensor on pin 3
const int touchPin = 3;

//store the time when last event happened
unsigned long lastEvent = 0;
//store the state of LED
boolean ledOn = false;

//setup pins
void setup() {
  pinMode(ledPin, OUTPUT);
  pinMode(touchPin, INPUT);
}

void loop(){
  //read touch sensor state
  int touchState = digitalRead(touchPin);

  //only interested in the HIGH signal
  if (touchState == HIGH) {
    //if 50ms have passed since last HIGH pulse, it means that the
    //touch sensor has been touched, released and touched again
    if (millis() - lastEvent > 50) {
      //toggle LED and set the output
      ledOn = !ledOn;
      digitalWrite(ledPin, ledOn ? HIGH : LOW);
    }

    //remember when last event happened
    lastEvent = millis();
  }
}

Touching the touch sensor will light up the LED, but will not do anything as long as user keeps touching the sensor. Releasing the sensor and touching it again will turn off the LED and so on.

P.S. Loving my Rigol DS1052E digital oscilloscope. It’s a real eye opener to electronic signal debugging. Fantastic piece of kit.

There was a lot of excitement in the hardware hacker community back in May 2012 when VIA announced APC.IO – a $49 all in one Android PC. I was excited too, but my excitement quickly faded away when I received my two APC’s a few weeks ago and booted them up…

Quick overview in pictures

APC comes very well packaged

Nice little box

First glance at the contents

Contents unpacked: charger, USB cable to connect to PC, sticker, board and case plate

Hooked up and connected

Size comparison with Raspberry Pi and MK802 Android PC inside a USB stick

The good

• Relatively small form factor
• Wide range of connectivity options: HDMI, VGA, 4xUSB, LAN, audio in/out
• Micro SD card expansion
• Kernel and Bootloader available for download

The bad

The price – it’s just crazy! The board itself costs just $49, but delivery charge for two of them was $43! So the price of the board came to $70.5 and that’s a lot considering that it’s only a bare board without a case. Some people complained that they received import charges bumping the price even more. For the same price, you could get a lot nicer package and better performance by purchasing MK802 or one of it’s clones.

US plug for UK customers – you will need an adapter to get it to work.

The performance is unsatisfactory. It takes 30s to boot! It comes with Android 2.3 without Android Market out of the box and very limited amount of application preinstalled. Android Market can be installed though. I could not get the full HD version of Big Buck Bunny movie to play consistently on the HDMI output. After a few seconds it kept bumping back to VGA output. I suspect that maybe it was overheating?

No official support for other operating systems like Linux. This is a huge disappointment, because Linux could make the device a lot more useful and powerful. Android that comes with it is just too limited.

The verdict

The price is just too high. It would make it a lot more attractive if it cost somewhere around $35 with a reasonable delivery charge. It desperately needs a Linux port to be able to use the full potential of the device. With all the limitations the slogan “A bicycle for your mind” just does not make sense.  I should strongly suggest looking for alternatives and avoid buying APC.IO for now until it’s a lot more open, has all detailed header pinouts and most importantly – a fully featured Linux port.

Once that’s done, the device will appear as /dev/ttyUSB0. The only problem is that file permissions for the device are 660 so you won’t be able to access the device unless you are root or set the permissions to 666 with

sudo chmod 666 /dev/usbTTY0

Note, that you would have to do this every time you forward the device or start the guest VM.

A more elegant solution exists (at least in Ubuntu). Just add yourself the the dialout group:

sudo adduser your-user-name dialout

Reboot your PC and you will be able to access the serial port without anything extra just by forwarding it to the guest Linux OS.

amixer sset Master mute

amixer sset Master unmute

amixer sset Master toggle

For some reason, muting works fine, but unumuting or toggle has no effect. Upon further investigation I noticed that by muting Master channel, “PCM” and “Master Mono” channels are muted too. Unmuting Master does not unmute those two channels. I could have solved this issue by running a bash script that mutes the sound with

amixer sset Master mute

… and unmutes all channels with

amixer sset Master unmute
amixer sset PCM unmute
amixer sset "Master Mono" unmute

… but what fun is that? You can however mute and unmute with pactl. This requires just a single command line per action:

pactl set-sink-mute 0 1
pactl set-sink-mute 0 0