Hacking a Christmas Tree for Less Blinkyness

Hacking a Christmas Tree to Blink Slower

What good is a fiber optic self-lighting Christmas tree if it flashes so fast it will put you into an epileptic attack? The answer is “Not very good”, if you ask [Mads Nielsen] a.k.a [EcProjects]. So [EcProjects ] started a little project to slow the Christmas tree’s blinkyness down to a more reasonable rate. The task didn’t seem too difficult at first but turned into a quality tutorial building a variable frequency H-bridge motor control.

After opening the base of the tree [EcProjects] found a 12 volt AC geared synchronous motor turning a multi colored translucent plastic disk. A bright spotlight was shining upwards through the turning disk into the ends of hundreds of small fiber optics. This mechanism dumps loads of multi colored light out the ends of the fibers at the tips of the Christmas tree branches as the disk turns.

His goal was to slow down the motor; however, the rotation was based on the 50 Hz mains signal. In order to continue using this motor a lower frequency AC power source was needed. What follows in the video is an excellent lesson on how an AC synchronous motor works plus how to build a variable frequency control and H-bridge using some transistors, resistors and CMOS 4069 inverter chip.

In the end the frequency drive could only be lowered to about 30 Hz before the synchronous motor would stall and reverse using his design. [EcProjects] was bold enough to include several fails which always provides more opportunity for learning and is greatly appreciated.

If you believe you have a better solution please share your idea in the comments. I’m sure the first proposal will include an Arduino and servo modified for continuous rotation, but any solutions would be fascinating including modifications to his design. You can join us after the break to watch the video.

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Wireless Temperature Control for a Microbrewery

Wireless Temperature Control

When brewing your own beer, temperature control is important. If the temperature isn’t regulated correctly, the yeast will be killed when it’s added to the wort. It’s best to cool the wort from boiling down to about 25 C quickly before adding yeast.

To do this, [Kalle] came up with a wireless temperature controller for his home brewing setup. The device uses a heat exchanger to cool the wort. An ATmega88 connected to a H-bridge controls a valve that regulates flow through the heat exchanger. It reads the current temperature from a LM35 temperature sensor and actuates the valve to bring the wort to a set point.

A neat addition to the build is a wireless radio. The nRF24L01 module provides a wireless link to a computer. There’s an Android application which communicates with the computer, providing monitoring of the temperatures and control over the set point from anywhere [Kalle] can get an internet connection.

Motor drivers: half h-bridge with brake and more

Here’s a nice little circuit that will drive a motor and allow you to stop its rotation, giving your robot a set of brakes. It’s part of [JM's] post about the in’s and out’s of building microcontroller friendly motor controllers (translated).

This particular setup is a half H-bridge. It allows you to drive the motor in one direction only. The MOSFET used on the ground-side of the motor doesn’t actually need to be there. This is the brake which let you electronically stop the motor from spinning. Without it, the motor will keep turning under its own momentum when the half-bridge is shut off. Depending on the application this can be a big problem. There’s a great demonstration of the circuit braking a fast spinning motor in the video clip below the fold.

It is possible to use this driver with PWM, but [JM] has some warnings about inbuilt functions like FastPWM. Make sure you read his admonition, and if you need a refresher don’t miss this Hackaday video segment.

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Tinywrench controls motors with ATtiny24 chips

Tinywrench is [Tanjent's] take on a motor controller board. It aims to replicate all of the functions that a standalone motor controller chip offers at as low a cost as possible. Early results are in. It works, and as seen can be assembled for about $8.

The top of the device offers a terminal block for connecting motors, ground, and 24V input. A pin header on the bottom has all the connections you would expect to find with a stepper motor driver board. Looking back on top there’s also a pair of ATtiny24 chips, each with its own trimpot for balancing the constant current output. Hiding on the underside of the board are two H-bridges built using high and low-side MOSFETs along with some diodes for protection, and various passive components for driving them.

As it stands, each of those H-bridges can handle around 9 amps which should be more than enough for projects with small motors. [Tanjent] mentions that one of the main advantages of working with this instead of a single motor-driver chip is that if you fry one of the MOSFETs you can replace it instead of trashing the entire board.

Motion detecting window closers keep train noise at bay

motion_detecting_window_closers

[Ed Rogers] has the unfortunate privilege of living right next to a set of train tracks, and as a man who holds his sleep in high regard, he needed to find a way to keep the noise in his bedroom to a minimum. To combat the sound of passing trains, he built himself a system that automatically closes his windows when a train passes by his apartment.

The setup relies on a web cam, which uses motion-sensing software to detect a passing train. The video is analyzed by a computer in his room which passes a message to an Arduino when a train is near. The Arduino then sends a pair of window mounted linear actuators into action, slowly (and quietly) shutting his windows.

The linear actuators move pretty slowly as you can see in the video below, but we doubt that matters. Since it looks like [Ed] lives in a slow zone, it likely takes quite a bit of time for a freight train to pass, making the 40-second closing period more than reasonable.

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DIY Segway recycles broken electric scooters

[Petter] built himself a DIY Segway out of a couple of cheap electric scooters. We’ve seen a couple of very nice Segway builds in the past like the all analog Segway, or the creepy walking version, [Petter]‘s Segway build seems like it would be a useful human transport device.

The motors, chains, gears, and wheels are scavenged from a pair of electric scooters. Steering left and right is accomplished by tilting the handlebars left and right. The handlebars themselves are attached to the joint at a base that allows them to be taken on and off. We’re thinking this would be great for throwing a [Petter]‘s Segway in the trunk of a car – a design feature the original Segway doesn’t have.

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Intro to DC motor control using the SN754410

So your electronic hobby skills are coming along quite nicely but you’re not very comfortable doing more than blinking a few LEDs. Now’s a good time to try something new by driving a couple of DC motors.

You probably know that you can’t just hook these up to the pins of your favorite uC and call it good. The motors draw a lot of current (especially if they’re strained in lifting a heavy load) which would burn out your logic circuitry. Add to this the excess induced current that is generated when a spinning motor is shut off and you’re going to need a control system that can handle these dangers.

Enter the h-bridge motor driver. [Chris] has guided us through the process of building and using a H-bridge in the past. This time he’s using a motor controller that has four half H-bridges built into it. He hooks up the SN754410 to two motors, giving him speed and direction control for both based on the duty cycle of a PWM signal entering the chip for less than $2.50. Check out the video after the break for an overview of his methodology, then work your way through the multi-page post that he recently published.

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