Computing stuff tied to the physical world

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Horizontal JeeBot

In AVR, Hardware on Jun 1, 2009 at 00:01

The JeeBot has made its first explorations, using a Nunchuk controller:

JeeBot baby steps

It drives on two wheels plus a coaster ball to support the batteries – although not very fast and veering slightly to the right. It will also turn, by rotating the servos in opposite directions. The batteries push down hard on the coaster ball, making the wheels slip when turning if the surface is not hard enough. The control mechanism is somewhat proportional, although it seems to work best by just pushing the joystick to its limits.

Here’s the current primitive control loop:

Picture 1.png

Some more close-ups:

JeeBot baby steps

From left to right: the Wii adapter, batteries with coaster ball underneath, on-off switch, JeeNode, and the edge of the servos.

Not much wiring needed to get it going:

JeeBot baby steps

The two resistors divide the battery voltage in half, so it can be measured by an ADC pin. Note the use of wire to “bundle up” the Nunchuk I2C “bus”.

Port layout so far: 1 = unused, 2 = left servo + battery level, 3 = right servo, 4 = Nunchuk via I2C.

I’ve also mounted the gyroscope (not connected yet) in the proper orientation to sense rotations around the wheel axis:

JeeBot baby steps

Will need to add an accelerometer as well, no doubt.

The center of gravity is just about on the power-switch, between the battery pack and the JeeNode. Which is quite low when this thing is placed upright, not sure the servos + control loop will respond fast / accurately enough for balancing.

Current consumption is around 30 mA when idle, 160 mA with wheels turning freely, and up to some 300 mA under load – these 4 NiMH batteries give about 5.2V under no load when full, but I’ve seen it drop to 3.7 V under load after a bit of use – not so good…

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Servo fun

In AVR, Hardware on May 24, 2009 at 00:01

Here’s some fun with a servo:

Servo fun

A slider drives the two servos in opposite directions, so you can make this thing turn on the spot.

Here’s the sketch:

Picture 1.png

Had to use SoftwareServo instead of the Servo library which comes with Arduino IDE 0015 – which didn’t work for me.

Turns out that only pulses from 1.4 to 1.6 msec actually have any effect on the speed of the servos, the rest of the 1.0 .. 2.0 msec range just makes them run at full speed. These ara Parallax (Futaba) Continuous Rotation Servos.

Note that the servos are driven from the PWR line, i.e. the full 5V – but the servo pulses are 3.3V, like the rest of the JeeNode.

It’d be nice to use a Wii Nunchuk controller as input. Even more fun would be an accelerometer / gyro combo to turn this thing into a self-balancing bot …

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All together now

In AVR, Software on Feb 22, 2009 at 00:01

It’s time to combine everything:

Combi demo

This is a setup with all the sensor interfaces documented in recent posts:

  1. a SHT11 to measure relative humidity (and temperature)
  2. a BMP085 sensor to measure barometric pressure (and temperature)
  3. PIR + LDR sensors to demonstrate reading digital and analog signals
  4. a Nunchuk with 2-axis joystick, 3-axis accelerometer, and 2 buttons

A new “combi_demo” has been added to the Ports library. The code is essentially the concatenation of the individual demo source files (you can browse the real thing here):

Combi demo

This example illustrates how the Ports library lets you mix and match drivers and ports at will. Note that two I2C interfaces are running in parallel at different speeds (sure, the BMP085 and the Nunchuk could also have been tied to a single port, running at 100 KHz).

Sample output;

Combi demo

This example compiles to 9114 bytes of code with the Arduino 13 IDE, so there is still plenty of room left to add, say, a wireless driver.

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Hooking up a Nunchuk

In AVR on Feb 21, 2009 at 00:01

The Nintendo “Nunchuk” controller is for the Wii game console, but it’s also a great I2C input device. So for fun and as a game… I hooked one up to port 4 of a JeeNode:

Hooking up a Nunchuk

Although the “Wiichuck” adapter lets you connect an unmodified Nunchuk, I just ripped the whole thing apart, and cut off the proprietary connector. There are four wires, tied to pins 2..5 of port 4, respectively: green (SDA), white (GND), yellow (SCL), and red (+3.3V). The following “nunchuk_demo” has been added to the Ports library:

Hooking up a Nunchuk

Sample output:

Hooking up a Nunchuk

PS. I2C on port 4 = (on Arduino) SDA: D7, SCL: A3 (see JeeNode-v2.pdf page 3).

Update – swap the red and yellow wires for the JeeNode v3 and v4 (the above is an older unit).


Nunchuk

In AVR on Nov 9, 2008 at 00:45

The Wii Nunchuk controller is really just an I2C device, with a triple-axis accelerometer, an X-Y proportional joystick, and two push buttons. Breaking it out of its case allows us to connect it in ways it was never meant for:

EC19CAFA-DD22-4B24-8A54-DD7B726365D1.jpg

It’s very easy to hook up to an Arduino and there’s a good example on the web to read out all the sensors. I’ve tweaked it a bit to use pins 8 and 9 as the I2C/TWI interface.

Connections above are as follows: red = +3.3..5V, white = ground, green = SDA, yellow = SCL.