Simple sensors to calculate RPM

Ever wonder how to calculate revolutions per minute using a microcontroller? This project shows you how by purposing an IR emitter and detector and a computer fan. As the fan blades spin they disrupt the beam of infrared light between the emitter and the receiver. This results in a waveform on the receiver’s circuit which can be easily used to trigger interrupts in any microcontroller. In this case a PIC 18F452 monitors the detector’s signals for a rising edge. By measuring time data between interrupts the period can be established and RPM calculated. You can see a video of the test rig after the break.

So what can you use this for? It’s the method that most spinning POV displays use to stabilize the display. You won’t be limited to an IR sensor, but can use a hall effect sensor in the same basic fashion.

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Add-on panel brings automated vents flaps to a PC

[SXRguyinMA] built a replacement top bezel for his computer case. He wanted to add vents that would automatically open or close based on the cooling needs of the computer. With some careful measurements he modeled the parts in Sketchup and sent out for them to be cut from styrene with a water jet cutter. The parts came back looking great and the assembly of the shutters went swimmingly. The bezel also includes a lighted screen for temperature information, as well as the front USB ports, headphone and mic jacks, etc. Hidden underneath is an Arduino board and servo motor. The Arduino polls the temperature and drives the servo to adjust the fins accordingly. There’s even a supercap in the circuit that will close the vents when the PC powers down or when power is unexpectedly lost. See it in action after the break.

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Serial port controlled CPU fan

[Christian] was running a Linux box as a home server but needed a way to quiet the noisy machine. Like many Linux servers, he’s using some pretty old hardware which doesn’t have an on-board header for the CPU fan which generates much of the unwanted sound. Those headers are nice because software can monitor the CPU and board temperature and adjust the fan accordingly.

[Christian's] solution was to use the serial port for the task. He built a small circuit in which serial pin 3 drives the base of a transistor, pin 5 provides ground, and a floppy drive power cable supplies 5 volts. From there he wrote a RUBY program to monitor the CPU temperature and generate a PWM signal on the serial port, throttling the fan speed as needed.

[CC Photo Credit: Garrette via Flickr]

BAMF2010: Look sir, droids!

Ask any engineer what originally sparked their interest in technology, and almost universally the response will be a Hollywood film or TV robot — Star Wars’ R2-D2, the B9 robot from Lost in Space, or Short Circuit’s Johnny 5, to name a few. Engineers need a creative outlet too, and some pay homage to their inspirations by building elaborate reproductions. At this year’s Maker Faire, droid-builders had their own corner in the center hall, their work ranging from humble craft materials to ’bots surpassing their film counterparts in detail and workmanship.

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PWM fan controller for external hard drive

[Alan] noticed that his external hard drive was getting quite hot to the touch after a few hours. He says that it was probably designed to handle the heat sufficiently, he thought it would be fun to beef it up. He’s using a pic 12f675 microcontroller as the brain and an LM35 temperature sensor. The Fan speed is varried in 8 steps from 35 degrees C to 45 degrees C.

Fan-powered skateboard

[Chris Neal] is starting his hacking career young. He built this fan-powered skateboard for his fourth grade ‘Invention Convention’. The ideas were his own but he had some help with the construction from his uncle who owns a repair garage. On the back of the board there’s a motorcycle battery that powers the fan. We’re not sure where that fan came from, but apparently it can push a rider at about 3-5 MPH. [Chris] scored a free MacBook pro from this hack after being featured on the Ellen DeGeneres Show.

For some reason this sparks the memory of the drill powered minibike.

[via Gizmo Watch]

LED and fan controller

Needing a front fan to keep his hard drive cool, [CalcProgrammer1] found he was unhappy with a single LED color for the fan. He swapped them out for a set of four RGB LEDs and whipped up his own controller board for the unit. It is based around an ATmega168 and patches into the COM2 header on the motherboard, providing a serial interface. [CalcProgrammer1] wrote a GUI to control fan speed, and individual LED color settings. You can take a look at and enthralling, edge-of-your-seat demonstration of how slider controls work after the break. Wouldn’t it be great if the HDD LED clock could be adapted to use a fan so that the front panel had a colorful analog dial on it? [Read more...]