Fingertip Heart Rate Monitor

February 17, 2011 by Chris Nelson 12 Comments

[Embedded lab] has a nice tutorial on building your own heart rate monitor. The monitor works by shining infrared light into the fingertip and looking at the changes in the reflected infrared signal caused by a heartbeat. The IR detector produces a very small AC signal so a couple of op-amps are used to filter and amplify the signal. The output of the filter circuit is then read in by a PIC16F628A, which counts the beats and displays it on a seven segment display. This might be a good project to try if you’ve got your microcontrollers down and you are looking to learn some analog electronics. Its noted at the end that the two main problems with building a circuit like this are going to be cross talk and adjusting the filters. The infrared diode and receiver should be close to each other to allow maximum reflection but you also need to make sure that you don’t allow the emitter to shine directly into the detector because the reflected light will be drowned out by the bright emitter.

[via make]

Your First Digital To Analog Converter Build

February 17, 2011 by Mike Szczys 16 Comments

Have you ever built a Digital to Analog Converter before? This is a circuit that can take the 0 or 5V coming off of several digital logic pins, combine them together, and spit out one analog voltage that represents that value. If you’ve never made one, here’s your chance. [Collin Cunningham] over at Make put together another lab video about DACs which we’ve embedded after the break.

The circuit above uses an R-2R resistor network – often called a resistor ladder – which you can learn much more about from the reference page that [Collin] links to. Although a DAC in an IC package is by far the most commonly found application, we do see these R-2R networks in audio hacks from time to time.

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Electronic Tolling System

February 17, 2011 by Mike Szczys 8 Comments

For us the hardest part of any project is coming up with the seminal idea. Once in a while you just need to cheat by recreating an existing product. That’s what EngineersGarage did with this toll plaza project. If you take a look around the various tabs at the top of that article you’ll see that they’ve used an 8051 microcontroller to bring together a character LCD, RFID reader, and a keypad. From there it’s a slew of coding to add the functionality for reading multiple tags, looking up stored value, and creating a replenishment system. Sure, it’s not really of much use in this form, but it’ll give you something to do with those shiny parts you have sitting around, and it might just lead you down a path to something more meaningful. As usual, there’s a demonstration video of this after the break.

If this doesn’t float your boat, perhaps this other RFID access system is more your thing.

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Etching Panel Faces On The Cheap

February 17, 2011 by Mike Szczys 23 Comments

[James] came up with a way to make small numbers of high-contrast instrument panels cheaply, and without too much labor. We’ll make with the bad news right away; you’re going to need a laser cutter to use this method. Traditionally, panels that look like the one above are etched onto special composite that has one color at the surface and a contrasting color beneath. [James] started with plain old acrylic, etched his labels, then filled the voids with black wax crayon. Just scribble all over the etched face to rub wax into the grooves, go through a couple of cleaning steps using white spirit, then bake the panel to even out and harden the wax layer. He’s got several examples of his work, including medallions that are used to label LED indicators.

Propeller Platform Logic Analzyer

February 17, 2011 by Kevin Dady 20 Comments

[Wulfden’s] new gadget is a 28 channel 3.3 volt digital logic analyzer. Powered by a Parallax Propeller running at 100MHz (permitting a 10 nanosecond sampling rate), using all though hole parts, and open design so it is possible to whip up your own.

Data is collected and sent to a host computer running Propalyzer which looks to be a very nice logic analyzer front end, and sports all the needed features and a HP inspired design. The design of the board allows you to plug it on to any Propeller Platform board, and this is very handy for those who have other Propeller boards, though others will have to source a regulated 3.3 volt power supply, and serial converter.

Overall this looks to be a very handy tool to have around, whether you opt for the kit to use on your Propeller Platform boards or roll your own, the features and cost are very attractive if you need a logic analyzer.

Join us after the break for a quick introduction video by [Nick] (of Gadget Gangster)

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DIY Fizzy Fruit

February 17, 2011 by Mike Nathan 37 Comments

co2inator

[Rich] over at Evil Mad Scientist Labs took it upon himself to make eating fruit a little more enjoyable for his kids by infusing it with CO2 using his CO2inator. Observing the same principles used in making soft drinks and force-carbed beer, he decided to build a CO2 pressure chamber for use in his kitchen. He gathered a handful of easy to find components to construct his rig, including a household water filter housing and a CO2 cylinder from a paintball gun. He has some helpful hints for those who are not familiar with the process, noting that refrigerated fruit absorbs the gas more quickly than warm, and that considering the water content of the fruit is important when selecting what to carbonate.

Once [Rich] had everything safely connected and checked for leaks, in went the fruit. After about half an hour to an hour, the fruit was carbonated, much to the delight of his children. This looks like a quick and fun project for adults and kids alike, that can easily fit into a busy weekend schedule.

[via Neatorama]

Classical’s Greatest Hits On Hardware’s Greatest Flops

February 17, 2011 by Mike Szczys 19 Comments

We get a lot of tips about old hardware playing recognizable tunes. But once in a while one of these projects goes above and beyond the others and this is a shining example of great hardware music. [FunToTheHead] put together a music video (embedded after the break) that shows his custom MIDI device playing Bach’s Toccata in d minor. He left some comments that clue us into the way he did it. Most obviously, he’s using the stepper motors from four floppy drives to create precisely pitched sounds. Internally, a PIC 18F14K50 acts as a MIDI-over-USB device, taking commands for all 128 MIDI notes as well as the pitch bends associated with them. The first four channels are played directly on each drive and the other twelve are triaged among the hardware by the microprocessor. But for the results heard in the video you’ll need to code your MIDI files by hand.

Bonus points to the video editor for the Phantom’s floppy-laden appearance in the video… it’s good to laugh!

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