Toy Helicopter Hacking

This Christmas, my parents gave me a palm-sized toy helicopter (Avatar Z008), and my girlfriend’s parents gave me a slightly bigger toy helicopter with a video camera (Egofly Spyhawk). I also have one that I bought myself (Syma S107). All of them are gyro-stabilized, coaxial-rotor helicopters, which basically just means that they automatically don’t roll, and are easy to fly.

I had hoped to convert one of them into a tiny drone. I opened up the S107 this morning to take a look at the internal PCB. The IR signal from the remote goes to an unmarked 14-pin IC. The gyro (which I assume to be the little metal can mounted on a daugther board from the main PCB) is marked, with “C 146″ and “Y2373″. One pin of the gyro is grounded, one, marked “TLY” is connected to the unmarked IC, and one goes to Vcc. That is pretty clearly power, ground, and a signal pin.

This means any control that the system is doing based on the gyro is done by that unmarked IC. Chances are that re-implementing the gyro control would be amusing, but much harder than simply adding whatever drone control I decided to add “on top of” the existing hardware.

An easier approach would be to take advantage of work that other people have done on reverse-engineering the IR protocol, and add my own control circuit that sends IR control signals to the existing board. That way, the existing board would take care of driving the motors and keeping the helicopter balanced, while my board would add autonomy.

Downward and front facing versions of SpeckleSense could be used to give the helicopter a sense of its movement in the world, which might be good enough for dead-reckoning navigation over small distances.

Mindflex EEG Hacking

I got a Mindflex Duel for Christmas. The Mindflex Duel is a toy that uses a pair of EEG headsets to read signals from the users, and then send those signals to a base unit that contains a blower and a little sliding cart to move the blower. The users try to concentrate to control the cart, moving a little ball suspended in the air jet from the blower into a goal.

Needless to say, I gutted it.

The base unit has a little PCB with a 2.4Ghz radio on it, and a little hardware to control the blower and cart motors. The headsets are the really interesting part. Each one has a single-channel EEG and a wireless radio. I took the radios out and replaced them with BlueSmiRF bluetooth-to-serial links so that I could connect them to my laptop. The hardware part of the replacement is below, the software part will be in another post.

The guts of one of the headsets. The 2.4 Ghz radio is the top daughter board, the EEG hardware is the bottom daughter board.

I desoldered the original radio. It works in the same band as Bluetooth, and consumes power, so there was no need to have it there.

The red and black wires supply power for the BlueSmiRF. It can take up to 5 or so volts, but the headset runs on 4.5v, so it is fine to hook it up like this. The red wire is connected to the power switch, rather than V+, so that the power switch also turns off the bluetooth radio.

The white wire goes from the pin labeled “T” on the EEG board to the RX pin on the BlueSmiRF. The T pin of the EEG board is a serial line, which transmits the EEG data to the BlueSmiRF.

Glue the bluetooth radio into place with hot glue. The LEDs on the BlueSmiRF are covered by black paint on the inside of the Mindflex headset, but I scractched away the paint in little circles so the BlueSmiRF status lights would shine through.

The finished product looks stock, until you turn it on. That red light on the side is not normally there.

Toybrain further improvements

I populated one of the Toybrain V2 boards and gave it a bit of a shakedown. I still have to test the motor driver, but I’ve at least fixed the backwards ICSP header and the reversed TX/RX lines. I did add a LED for debugging, but then hooked it up to a ADC line, so lighting it up means losing an analog pin.

For those as don’t know, you can get the analog pins on an Arduino/ATMega168/ATMega328/whatever to act as a digital GPIO by treating it like one, using the aliases “A0″ through “A5″. Full instructions are here.

The V2 boards also have a reset button, which is very useful.

I’m already working on V3, which is going to be smaller. The V2 has headers for power, ground, and data for each pin, which I think is a bit much. I want that room back to build a voltage regulator and some filtering onto the board. The microcontroller can run at 1.8 to 5.5 volts, so the filtering is a bit more important than the regulation. However, some toys surely run at 6 volts or more, and would ruin the microcontroller, which is a SMD device.

So V3 will include filter capacitors, probably SMD, on the power rails, and a 3.3V regulator (The Micrel MIC5209-3.3 in SOT233 package looks good) or the option to short around it. The regulator only supplies the power for the microcontroller, so it won’t need to be very high power.

Again with the lasers

There is an Instructable up on using speakers as galvanometers for a laser projector. This looks just about optimal for the Nuiteblaster, as it provides readable text without defocusing or otherwise spreading the laser beam.

I’ve started building one, with a couple of modifications. Instead of resistors, I’m using diodes to snub the back-EMF from the speakers. I’m also using MOSFETS instead of transistors to switch the power to the speakers. MOSFETS have lower on-resistance than transistors, and so transfer more power and waste less energy as heat. They also have VERY low gate current (low enough to treat as non-existent for my purposes), so there’s no need for current-limiting resistors on the gates, although a resistor might be good to limit any ringing that might happen from slamming 5V into it. Since I’m driving it directly from a 5V microcontroller, gate drive and switching time hopefully won’t be a concern.

Welding

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.

ToyBrain at the Maker Faire

I’ll be at the Cambridge Mini Maker Faire (details here, here, and here) this Friday, showing off my ToyBrain boards, LED art, and other oddities. Look for the guy with the unnatural red hair.

Chris Connors was kind enough to include my work from 2010 in his post about the Faire.

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Photos from the Rhode Island Min Maker Faire a couple of years ago.

Finds

For anyone who has ever wondered where I get my ideas from, I find them in the trash.

I recently found a hollow Styrofoam cube, with one open side. It’s about 14″ on each edge, with walls about 1.5″ thick. I can just barely see overhead lights through it, so I imagine it will light up well with colored LEDs in it.

Furniture building

Most of my projects are on hold until I get a place to work on them. My current lab is about 11′ x 12′, with a little storage room off to the side. It’s not big enough to store my tools and provide a useful workspace, so I’m improving it in two ways.

The first improvement is to cut down on stuff. I own a lot of things that I’m not using, and don’t even have any really clear plans to use, so I’m collecting all that junk and putting it in boxes. Some of it is going to friends who are worse hoarders have clearer plans for it than me. Anything that people don’t take is going to have a chance to get sold at the MIT Flea Market in April, and then is going to get thrown away. Once I’m done getting rid of stuff, I’m going to start tagging things when I use them, and get rid of the stuff that I don’t use for a year. I’m not going to be terribly strict about this, but I am going to give it a shot, and see how much of the stuff I actually want when it comes time to get rid of it.

The second improvement is to make a useful workspace. I used to have a large corner desk, which I used for all sorts of work. Since I didn’t have space for that in my current apartment, I got a smaller desk from a friend. It’s a cute desk, but it isn’t useful. The top has drawers that open over the desk area, so you can only get at the contents of the drawers if you don’t have anything on the desk. That doesn’t happen with desks I own. Aside from that, it’s too small to accommodate tools, a computer, and a project, and since many of my projects involve both a computer and tools, this is a problem.

To replace the useless desk, I’m building a new workbench. It’s a standing desk, with a 5’4″ x 3′ upper surface made of birch plywood. The underside will have some space for storage and my computer. Since the computer desk and the work desk will be consolidated into one workbench, I’ll be able to get rid of both my computer desk and my current workbench, and both the chairs in front of them, and the pads that protect the floors from the chairs. I’ll probably keep at least one of the chairs around, in case I need it in the future, but it won’t be in my lab.

The category of this entry “B Work” refers to work which is intended to accelerate the thing you really want to do, which is your “A work”. “C work” accelerates your acceleration, and so very little of it needs to be done in comparison to the other two.