Keypad Input Scanning By A 555 Timer

March 3, 2011 by Mike Szczys 17 Comments

[R-B] designed a 555 timer circuit to scan a keypad. Keypads are common interfaces for small projects and require row and column scanning by a microcontroller. [R-B’s] setup allows you to reduce the number of pins used on the microcontroller to just two. One is an interrupt that is triggered when any of the buttons are pushed, the other reads the frequency from the 555 chip. Each button has its own resistance which alters the frequency of the 555. The microcontroller reads the frequency for 100ms using a timer. The number of timer overflows that occur during that period directly correspond to the button press (five overflows for the numeral 5, zero overflows for the numeral zero).

We usually debounce our button presses for 40 ms, this is more than twice that amount of time but still not a staggering difference. It does make us wonder if you will miss quick button presses? The only really way to know is to try this out yourself. Check out the video after the break and don’t forget to leave a comment with your own experiences in working with the circuit.

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Electronic Watering Can

February 7, 2011 by Kevin Dady 10 Comments

When [Deddies lab] was looking to keep their (rather large) Ficus Lyrata appropriately watered, they followed their motto, stuck a micro controller on it and whipped up an Electronic Watering Can .

The whole thing starts off with power that is switched on once a day for 15 minutes by a traditional mechanical lamp timer, and that is connected to a atmega8 micro controller running @ 1MHz which increments a counter by one. When that counter hits 7 the mega switches on a pump, watering the plant with roughly half a liter of water per week out of a bucket reservoir , which according to the article’s calculations should last about 4 months.

In order to assure that the pump does not run out of water a rubber duck was attached to a string, the other end is attached to a micro switch, and when the water gets too low the string is pulled, switching one of the micro controller’s pins low.

While we agree that it could use a low water indicator, that is trivial to add, and over all the project represents a great hack done on a Sunday using parts and materials already on hand. Join us after the break for a quick video too!

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Charging Timer For R/C Batteries

February 4, 2011 by Mike Nathan 27 Comments

arduino_controlled_socket

Santa brought [Quinten’s] son a shiny R/C truck for Christmas, but this new toy had one drawback – its batteries could only be connected to the charger for a maximum of 6 hours, lest he turn his house into a pile of smoldering ash. With grave warnings from the manufacturer dancing in his head, he searched around for a timer that would allow him to cut power to the battery after charging for its allotted time. Coming up empty, he decided to create his own timed electric socket regulated by an Arduino he had sitting around. He grabbed a project box and wired up a nice looking socket timer, complete with an LCD status display. To make things easy for his son, he added two buttons to the front of the controller – one for selecting the amount of charging time, and one to set the timer in motion. As with his previous hacks, [Quinten] has provided plenty of documentation in the form of pictures, code, and even a video of the timer in action.

$20 Fuel Injector Tester

January 16, 2011 by Mike Szczys 39 Comments

[Dino] is an auto mechanic and needed a way to test out fuel injectors. Commercially available tools start well over $100 and go up from there, but he built his own for about $20.

The injectors have a coil in them that needs to be tested. His design calls for a series of 0.008 millisecond pulses to test the coil. He started by setting up a 555 timer to output a one second pulse. This signal is fed into a second 555 chip that outputs the 0.008 pulses and in turn actuates a MOSFET to switch the coil on and off. To use it [Dino] connects to a 12V bench supply and to the injector, using a single button to start the test. See him explain the setup in the video after the break.

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Talking Poker Timer

June 18, 2010 by Caleb Kraft 7 Comments

[youtube=http://www.youtube.com/watch?v=k8iIuPnXzm8]

This interesting box of buttons is a talking poker tournament timer. Full of useful tools like a binary time display, words of wisdom, countdowns to the end of the game, and even good old “bicycle built for two” mode (around 1:20). While we find it fairly difficult to understand, we applaud the feature list, especially the song. He used an Arduino with a voice shield, so there’s not much to the electronics side, but you can download his source code from his site.

[via Makezine]

Biosphere Lighting

April 26, 2010 by Caleb Kraft 8 Comments

Sometimes, sitting in a windowless office can drive you crazy. Adding a little bit of life and color can really help. [Gripen40k] did this by building a biosphere. He didn’t have any windows though, so he made an LED light on a PIC based timer. What is interesting is what he did with a thermistor. The Cree LED bulb that he salvaged was going to be submerged in the water, so he had to do some workarounds to keep from over heating the biosphere. Read the project log for more details.

Wine Glass Time Keeper

January 16, 2010 by Mike Szczys 17 Comments

We’ve seen a glut of time-keeping projects lately. We guess time was the original motivator for technology so we’re okay with it (but we’re not calling ourselves Clockaday quite yet). This clock, or more appropriately this timer, is a homemade hourglass that [Andrei] put together. The finished look is simple but he put some real time into its production.

The glass portion is a combination of two wine glasses. He removed the stems, ground the bottoms flat, then drilled holes to allow the sand to pass. He used plumbers putty around the top of the upturned reservoir to create a temporary bowl of water which cooled the glass during drilling. This prevented cracking by keeping the friction generated heat at bay. Working with the glass took a total of around five hours.

To assemble, he epoxied the two wine glasses together, routed out a ring in the wood bases for the lips, and used dowels to connect the two ends. [Andrei] concluded that the gentle slope at the bottom of the wine glasses is not the ideal shape as some sand can get stuck in them. Perhaps champagne flutes for his next build? At any rate, we think it’s a unique, non-automated hourglass build.