Doubling down on motor drivers

Motor driver chip too weak for your needs? Just use two of them. That’s the advice which [Starlino] gives. He stacks motor driver chips to product move powerful controllers.

When stacked as shown, the driver combos should be able to drive at 4A. This is partly because he ganged together the outputs in pairs, and also because of the stacking. That’s a lot of juice, but [Starlino] documented his testing stage which shows that they’re up to it. It’s a bit hard to see from this angle, but he is using a serpentine heat sink. It snakes its way between the stack of chips, then over the top chip before folding back and spreading its wings. The motors he’s using have a stall current of 3.7A, and he included resettable fuses graded at a 2A hold current. He’ll be glad to have that extra protection is something goes wrong with the drivers.

[Thanks Roger]

Arduino Tachometer tutorial

This tutorial will guide you through the process of building a tachometer around an Arduino. Tachometers are used to measure rotation rate in Revolutions Per Minute (RPM). You don’t need much in the way of hardware, this version uses an Infrared beam to measure fan speed. As with last year’s PIC-based tutorial, [Chris] is using a character LCD to output the reading. Wiring and driving the LCD ends up being the hardest part.

An IR transmitter/receiver pair are positioned on either side of the fan. When the blade passes in between then, the receiver shuts off a transistor connected to one of the Arduino’s external interrupt pins. He shows how to use this interrupt to measure the amount of time between the passing of each fan blade. If you divide for the number of blades, and average the reading for greater accuracy, you can easily calculate RPM.

Another alternative would have been to use a reflectance sensor which allows to for the transmitter and receiver to both be on the same side of the fan.

Word clock of a different nature

This work clock functions in an unexpected way. With each passing second it displays a random four letter word on the right side of the display. Traditional word clocks tell the time in natural language, but this one is simply used as a learning opportunity.

[Iron Jungle] got his hands on the display for just five buck from Deal Extreme. Looks like the price has gone up two dollars but that’s still a bargain. He wanted to use all eight digits of the display, and was looking for an opportunity to control more than one i2c device at a time. He ended up rolling an EEPROM and DS1307 RTC into the design. He figured the could display 24-hour time on four of the digits, and pull a library of four-letter words off of the EEPROM to fill the rest. He grabbed a word list off of the Internet then used a Python script to remove words containing 7-segment unfriendly characters (K, M, V, W, X, Z). The final touch was to use a salvaged relay to give the clock a ticking sound. Hear it for yourself in the clip after the break.

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Building touch sensors from digital barometer chips

A couple of Harvard researchers have developed a method of using digital barometers as a touch sensor. The good news for us is that they’ve open sourced the project, including Eagle board files, firmware, and details about the materials they used.

The digital barometers were chosen for their characteristics, availability, and low-cost. The sensor uses an array of Freescale MPL115A2 chips, a MEMS Barometer designed for use in altimeters. The mass production makes them cheap (Octopart found some in single quantities for $1.71 at the time of writing). The chips are soldered onto a board which is then cast in rubber. This distributes the force while protecting the sensors. The video after the break shows them standing up to rubber hammer blows and supporting a 25 pound weight.

There are a few tricks to reading the array. The first is that the devices are designed to be used one-to-a-project so they have a fixed i2 address. A separate chip must be used to address them individually. But one it’s up and running you should be able to use it as feedback for the fingertips of that robot arm you’ve been building.

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PlayStation gaming on a NOOK Simple Touch

Improvements in processing power really hit home when you see an eBook reader playing PlayStation games. Sure, we’re talking about a system which launched more than 15 years ago (the original PlayStation launched way back in 1995), but this is a $99 device which seems to be playing the games at full speed!

[Sean] wrote in to share the project with us. After rooting the device he installed System 7 (aka Mac OS 7) using Mini vMac for Android. He uses Free PlayStation Emulator (FPSE) to run the games. There is an Android version which provides the touch-screen controls you see above. We figured the graphics would be awful, but the video after the break proves us wrong. Other than being in black and white we think the graphics are fantastic. Just one hack was necessary to make this happen. [Sean] uses NoRefresh to keep the Nook from refreshing the screen which is what causes the film-negative type of flashing after several page turns.

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Can a Kickstarter project actually build a space elevator?

It’s the stuff that Science Fiction is made of: an elevator that climbs its way into space rather than needing a rocket to get there. Can it be done? No. But this Kickstarter project aims to fund research that will eventually make a space elevator possible. They’re already way over their goal, and plan to use the extra funds to extend the reach of the experiments.

A complete success would be a tether that reaches into space, held taught by a weight which is pulled away from earth by centrifugal force. That’s not really on the radar yet (last we heard humans weren’t capable of producing a substance strong enough to keep the tether from snapping). What is in the works is a weather balloon supporting a ribbon which a robot can climb. The team isn’t new to this, having built and tested several models at University and then in a start-up company that closed its doors a few years ago. Now they’re hoping to get a 3-5 kilometer ribbon in the air and to build a new robot to climb it.

For now we’ll have to be satisfied with the 1000 ft. climb video after the break. But we hope to see an Earth-Moon freight system like the one shown in the diagram above before the end of our lifetimes.

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Portable radio station gets a beautiful case

[Martin] put together a simple portable radio unit to take some MP3s with him while he’s out and around. The build was simple; just a no-name Chinese MP3 player, a battery, and an FM radio transmitter. To give his project a little more pizzazz, he came up with a very handsome laser cut wooden case to turn what would be a bunch of wires and components into an attractive build.

[Martin]’s case makes wonderful use of the kerf bending technique. By cutting small staggered lines in a piece of plywood, [Martin] was able to bend his laser cut enclosure into a surprisingly tight radius. With the help of a pair of laser cut forms and a bit of hot water and glue, he was able to make the shape of his case permanent.

The top and bottom of his case are also laser cut plywood, but [Martin] included a translucent plexiglas logo on the top. When his radio unit is activated a LED inside his project box lights up, illuminating his personal logo.

Kerf bending is something we’ve seen before, and we’re looking forward to seeing more project boxes use it in the future, hopefully with the application of a veneer to cover the diamond-shaped holes.