Month: August 2011
I have three head-positioning assemblies from CD-ROM drives. In the drive, they would move the optical components around to read the various parts of the disk. Removed from the drive, I’m planning to use them to make very small CNC machines. The head positioning assemblies use bipolar stepper motors, which turn a threaded rod, which draws the optics along.
Normally, I use the electronics from floppy drives to control stepper motors. The floppy drive interface has step and direction pins that directly control the motor used to position the head of the floppy disk drive.
Unfortunately, all of the floppy drive motors I have around used unipolar stepper motors. This makes driving them slightly easier, as power is supplied to the motor on one wire, and all the other windings are driven with current sink drivers. As a result, each winding is either on or off, but the current always flows through it in the same direction when it is powered.
All the stepper motors I have are bipolar stepper motors. Instead of current sink drivers, they are driven by a driver that can reverse the direction of the current flow through the motor windings. I can think of ways to drive a unipolar motor from a bipolar driver, but I’m not seeing any good way to drive a bipolar motor from a unipolar driver.
I may end up just building my own drivers, and running them with an Arduino or other microcontroller. I have all the parts, and it’s certainly cheaper than buying a bunch of drivers.
Xybernaut Head Mounted Display to VGA hax!
I have a Xybernaut Xyberview HMD, which originally connected to a Xybernaut MA-V or MA-IV wearable computer. Xybernaut went out of business after some questionable corporate shenanigans, but while they were around, they made a solid product. Unfortunately, they used a custom, or at least obscure, connector to hook that solid product together.
Thanks to the Wayback Machine, I’ve found the pinouts for the connector, and wired mine up so that it takes a standard VGA input. I also built a power supply for it, because it needs 5V and 15V power. The power supply takes 15V from a laptop power brick and drops part of it to 5V while also providing a 15V pass-through. I used a switching regulator, because otherwise I’d be dropping 10V at unknown current as heat.
I initially had the red and blue lines of the VGA connector crossed, but I think that is because they are crossed in the instructions that I found. My corrected pinout is below. If you happen to actually be equipped to do this hack, please do let me know if I made an error, and your terribly expensive, extremely obscure hardware from the mid ’90s somehow fails to work.
The HMD connector has two rows of pins in a connector that looks a little like a miniature Centronics connector. Assuming the longest edge of the connector is on top, there are 13 pins in the upper row (U1-U13) and 13 pins in the lower row (L1-L13).
Wire colors are described as the color of the wire, the color of the mark on it, and whether the marks are sparse. So Yellow/Red (sparse) means a yellow wire with a red mark on it that is less dense than the wire described as Yellow/Red. You’ll know it when you see it.
Signal Name Xybernaut Wire Color VGA Pin Red L4 Pink/Red (sparse) 3 Red ground L3 Pink/Black (sparse) 6 Green L2 Yellow/Red (sparse) 2 Green ground L1 Yellow/Black (sparse) 7 Blue U14 Gray/Red (sparse) 1 Blue ground U13 Gray/Black (sparse) 9 H Synch L6 White/Red (sparse) 13 V Synch L7 White/Black (sparse) 14 Synch ground U10 Pink/Black 10 +5V U1 Gray/Red +5V U2 Yellow/Red +5V U3 White/Red +15V U5 Pink/Red Digital ground L13 Yellow/Black 5 Digital ground L10 Gray/Black Digital ground L5 White/Black Analog ground U8 White Headphone out L12 Pink Mic in U7 Yellow HMD Sense L8 Gray 11
I connected the Gray/Black and White/Black wires to the ground of my power supply, the Yellow/Red, Gray/Red, and White/Red wires to 5V, and the Pink/Red wire to 15V. The display powers up, and I can drive it from my laptop using 640×480 resolution at 60Hz.
Unfortunately, none of this hacking changed the fact that wearing an HMD makes you look like a cyborg from space.
Brain Transplants for Toys
I have a bunch of old toy skeletons sitting around. They are not toy versions of the bones of animals, but the frameworks and some of the motors from things like a toy tracked robot, an RC truck, a few toy robot insects, some tiny RC cars, a robot base with continuous-rotation servos, and so forth. All of these things have motors or servos in them. All of them need some form of controller to make them into autonomous robots to do my bidding (or wander around banging into things).
To that end, I’ve developed a little embeddable controller around the ATMega8, ATMega48/88/168, and other pin-compatible microcontrollers. That is the same chip used in the Arduino, so my board will be software-compatible with the Arduino as well.
My controller, which I’m calling ToyBrain, has a pair of 1A (stackable for more current) H-Bridge motor drivers, so it can control up to four motors in one direction, two motors bidirectionally, or one stepper motor. It also provides two headers for servo motors. For inputs, it has four analog or digital inputs and two digital inputs that are connected to interrupt lines, so it can do things like handle bumper switches in an interrupt service routine.
I’ve ordered 10 boards. When they arrive, I’m going to populate them with whatever chips I have around and try to get a few of my old toys running. Assuming everything goes well and I get a polished device together over the winter, this may end up being something I sell at the MIT flea regularly. I’ll hook up a bunch of toys with the same controller, to show off its versatility, and offer the controller as a kit people can buy.
I’m working on a project to make inflatable sculptures that react to contact. The inflatable shapes are sewn together out of materials like umbrella fabric and ripstop nylon. Those fabrics block air well, and so a shape made of them can be inflated by a fan.
I am planning to have them react to contact by monitoring the speed of the fans that inflate them. If the inflated shape is pushed, the air pressure in it will increase, and escaping air will try to turn the fan backwards. This should show up as a decrease in fan speed, which I can detect with a microcontroller. The fans are computer cooling fans, so they already have speed sensors built into them. The speed sensors were originally intended to allow the computer that the fans cooled to detect fan failure and shut down gracefully.
I have a couple of inflatable shapes together, but I need a beefier 12V benchtop supply to run them. each fan draws 1.1A at 12V. That is a lot more than a normal computer fan, but these are high-volume server cooling fans, so they move a lot more air.