Light-sensing circuit for power saving applications

light_sensing_circuit

Instructables user [MacDynamo] was thinking about home security systems and wondered how much electricity is being wasted while such systems are powered on, but not activated. He pondered it awhile, then designed a circuit that could be used to turn a security system on or off depending on the time of day, but without using any sort of clock.

His system relies on a 555 timer configured as a Schmitt trigger, with a photoresistor wired to the reset pin. When the ambient light levels drop far enough, the resistance on the reset pin increases, and the 555 timer breaks out of its reset loop. This causes the circuit to power on whatever is connected to it. When the sun rises, the resistance on the reset pin drops and the 555 timer continually resets until it gets dark again. He notes that this behavior can be easily reversed if you were to put the photoresistor on the trigger pin rather than the reset pin.

We like the idea, though we are a bit wary about using this for any sort of real security system. An errant insect or debris could cause the system to be turned on, and we’d feel pretty foolish if someone disabled our alarm with a flashlight. That said, this sort of circuit still has plenty of practical, power-saving applications outside the realm of home security.

Adjustable prank box growls and screams

growling_altoids_tin

[Brett] over at FightCube was tossing around ideas to build a screaming prank circuit that fits inside an Altoids tin. Sound familiar? We featured a story just a few days back about the construction of a very similar item by [Dino Segovis]. It seems that great minds think alike after all!

[Brett’s] version is a bit more robust than the one we featured the other day. It’s similar to [Dino’s] in that it uses a 555 timer in astable mode, triggered by a normally-closed microswitch when the tin is opened. However, this version also includes a photoresistor which is used to increase the pitch and speed of the output as more light enters the box. This creates a growling effect that builds up into a scream as the box is opened. [Brett] has also included an adjustable pot which allows the sound range to be tweaked to his liking.

Stick around for a video walkthrough of the screamer circuit as well as a demo of the Altoids tin in action.

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Screaming Altoids tin just in time for April Fool’s

altoids_screamer

Maker [Dino Segovis] has started on a project he calls “Hack a week” where he will be putting together one hack or project per week, for a full year. The first installment of his video series was finished just two days before April Fool’s, and appropriately enough covers the construction of a circuit you can use to prank your friends.

The “Altoids Screamer” is a simple circuit based on a 555 timer that he built into a standard Altoids Tin. The 555 timer is used to generate a loud pitched squeal whenever the tin is opened. This is accomplished by wiring up the 555 in astable mode, and connecting it to a speaker to output the sound. A micro switch is installed inside the tin to detect when the top has been opened, triggering the “scream”.

While it’s not the most complex circuit we’ve seen, it definitely gets the job done and is easy enough to build in time for tomorrow’s festivities. It is a great hack for the office, the library, or any other quiet place.

Continue reading to watch [Dino's] first Hack a Week video demonstrating the prank’s construction. If you are interested in some more of his work, be sure to check out this automatic ball launcher and this other 555 Screamer toy.

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Real life Super Mario coin block

mario_coin_block

Instructables user [Bruno] recently constructed a fun little toy that brings a bit of the Mario nostalgia out of the video game universe and into ours. His Super Mario coin block is instantly recognizable from the first Mario game and performs just as you would expect it to. Punching or tapping the bottom of the block releases coins one at a time, complete with sounds straight from the game.

The coin block is constructed from thick cardboard and wrapped in color mock ups of the in-game block. Inside, a spring-loaded tube of coins is placed above a launch arm which is also connected to a spring. A servo actuated arm pulls the launch arm down, dropping a coin from its tube on to the launch arm which is then flung from the top of the box once the servo arm rotates far enough. When this occurs, the built-in MP3 player is triggered to play the “coin sound” from the game. A 555 timer is used to ensure the servo actuated arm rotates once per activation, and a LM386-based amplifier is used to increase the output volume of the MP3 player, both of which operate using rechargeable batteries.

Be sure to check out some of the inner workings as well as the final product in the videos embedded below.

[Thanks, Samjc3]

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Hardware-based security keypad keeps it simple

hardware_keypad_lock

Instructables user [trumpkin] recently built an all-hardware based keypad lock for a contest he was entering, and we thought it was pretty neat. The lock uses mostly NAND gates and 555 timers to get the job done, which makes it a nice alternative to similar software-based projects we have seen in the past.

The lock has 6 keys on the keypad, which is connected to the main logic board. The keycode is set using a series of headers at the bottom of the board, and you get 10 chances to enter the proper code before the board locks up completely. If this occurs, a “manual” reset via a button built into the main board is required before any more attempts can be made.

As you can see in the video below, the lock works quite well, but suffers from one shortcoming. Any permutation of the key code can be used to deactivate the lock, which is something [trumpkin] says he would like to improve in the future.

If you are looking for some more security-related reading, be sure to check out these other hacks we have featured in the past.

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Pint-sized Nixie display fits neatly in your pocket

[Brett] has had Nixie tubes on the brain ever since being introduced to them by a good friend of his. He decided that building a Nixie-based key chain would be the best way to familiarize himself with the technology, while also giving him a project to enter in the 555 Design Contest. He dug up the smallest Nixie tube he could find that displayed digits, and got down to business.

The biggest obstacle he ran into was figuring out how he would provide the high voltage required to light the Nixie tube. He eventually built a transformer circuit driven by a 555 timer, using a small 12v battery as his power source. Once everything was up and running on a breadboard, he designed and etched some PCBs, then soldered everything together.

The end result is a nifty little key chain that flashes the number 5 when a button is pressed – pretty appropriate for the 555 contest. It’s a great looking project, though we’re still not 100% sure what we think about a naked high voltage circuit residing in our pocket.

Keep reading for a pair of videos documenting the key chain’s construction and operation.

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Endless fun with LED dominoes

le_dominoux

Toppling dominoes is great fun for about 30 seconds at a time, when you are not busy setting them up for another run. [Randy] thought it was about time they got an electronic makeover to allow for constant, immediate gratification. Armed with a few simple electronic components, he has created Le Dominoux.

These LED-based electronic dominoes are actually quite simple to build. Each basic Le Dominoux is constructed on a small square of protoboard and consists of either a photo cell or phototransistor, a 555 timer, and an LED, all powered by a coin cell battery. The 555 timer, which is configured as a one-shot, is triggered when the photosensitive component on the back side of the domino is exposed to a bright enough light. The LED on the front end of the domino is then illuminated one time. This process is the electronic equivalent of a single domino toppling over.

He has constructed several variants of the Le Dominoux to act as flashing triggers, for outputting sound, as well as for turning tight corners. These variants allow the dominoes to be configured in many different ways, creating self-sustaining light shows. If anyone is looking for a fun project to introduce kids to electronics, this would definitely be it. Stick around to see a video of Le Dominoux in action – we bet you can’t stop watching it.

This is of course [Randy's] entry in the 555 Design Contest, which ends tonight at midnight EST.

[Thanks Jeri]

[Read more...]

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