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Building Your Own Glowing Cyber-Balls?
krezel asks: "So I've been drooling over the Ambient Orb, a cool little gadget 'glowing ball' that you changes colors based the 'health' of things you specify. It can do stuff like fade from red to yellow to green as your stock portfolio improves. However, being a poor college student I can't afford its $200 price tag. I've found lots of sources for super bright multi-color LED's. Cast a couple of them in some translucent resin, hook them up to a power source, and you've got yourself a cheap glowing ball. But I've yet to find any good information on how to build hardware that will let me control relays for devices like this through my serial or parallel port. Basically I'm looking for a cheap way to build a board that will let me control 4-8 relays (for each color) over my serial port, and some info on how to write the software for it. This could be a very cool project, and I plan on making the plans available, and the code Open Source, when I'm done with it. Any ideas?"
Of course controlling 8 relays or LEDs with the parallel port is much simpler.
Since the parallel port output is basically just TTL levels, just buffer it through a 74LS244 or something similar and use that to drive the LEDs directly. You can directly control each of the 8 data pins on a parallel port by writing directly to the base I/O port (i.e. port 0x378 is the default for LPT1). It's easiest to use inverting output with TTL driving LEDs.
Something like the following circuit:
D0 ---|>---/\/\/\---| D0 = parallel port data pin 0
/\/\/\ is resistor
|> is a buffer (i.e. 74LS244)
| (+5) is a 5 volt power source separate from the parallel port.
Make sure that the ground pin of the parallel port is connected to the ground of your circuit. For the 5 volts, a 7805 is a simple solution when using a separate DC power supply.
All of the above listed parts should be available at your local Radio Crap.
When D0 is 0 (low) current will flow from the 5 volt supply, through the LED and resistor and from the buffer to ground. When D0 is 1 (high), no current will flow.
When choosing a resistor, take into account the voltage drop across the LED. Blue LED's typically have a higher voltage drop than red or green. Red LEDs are typically around 0.7 volts whereas blue can be upwards of 3v.
Also make sure that whatever buffer you use can sink the appropriate amount of current. Most LEDs typically will take up to 15-20ma of current. It might also make sense to use an inverter instead of a buffer since the above circuit will cause a LED to light when the data bit is 0. a 74LS04 is a cheap easy-to-use inverter chip that is readily available.
With 20ma of current, choose a resistor based on the voltage.
Use the basic equation, V = I*R, where V is voltage in volts, I is current (in amps) and R is resistance in Ohms.
For example, for a red LED with 20 ma with a 5 volt source use:
R = (5 - 0.7) / 0.020 = 215 ohms. Since resistors come in standard values, choose the next highest value, i.e. 220 Ohms.
For blue, with a 3.6 volt drop you would use
R = (5 - 3.6) / 0.020 = 70 ohms. The closest match is 68 ohms, but it's usually best to error on the side of caution so choose the next larger value.
One thing you do not want to do is use the parallel port to drive LEDs or relays directly as you could possibly damage it. TTL outputs typically are not designed to output much current and are typically better at sinking current than sourcing it.
Note that I'm no expert on this and I'm sure you'll see better solutions listed here.
-Aaron
This post is encrypted twice with ROT-13. Documenting or attempting to crack this encryption is illegal.
Quick answer: combine RJ45 web server with serial relay driver and presto!
... google for it. They have all sorts of nice features (current limit, fault detection, cascadability and are controlable through the parallel port (you have to bitbang the data and clock bits). The webserver above has 3 general purpose I/Os - enough to control a relay driver.
There are lots of these serial relay drivers
But, you probablly want an actual A/D converter (preferably with a current output) or a digital potentiometer. There are lots of mfgs of these products, but Maxim is pretty liberal with samples (plus they have some neat innovative products!)
HIV Crosses Species Barrier... into Muppets
There are a ton of uses for it.
Note that people happily pay $30-50 for a little blinking light that tells them when they have voicemail. They'll pay a lot more than that for extra gauges on a car dash. And companies have paid millions for fancy "war room" conference rooms that continuously display important business data.
The basic prinicple is that people have to deal with a lot of invisible data, and if you can make it visible, it's easier for people to manage. Take a look, for example, at the many designs for in-house power meters. The idea is that if people have a better idea of how much electricity they're using, they'll waste less of it.
Personally, I would be tempted to hook it up so that it went slowly from green to red whenever I got behind on my email, a visible reminder of the people I'm ignoring when I get absorbed in a project. Or since I'm a freelancer, it'd be interesting to hook it up to a moving average of billable hours, so that I have a quick objective reference to check when I wonder whether a sunny day is better spent biking than coding.
Or at a company, I'd love to set it up so that it got redder and redder when people put in too much overtime on a project. Or you could hook it up so that it responded to an anonymous web poll on morale. And then perhaps another one tied to the number of open bugs. Or perhaps percentage of code covered by test suites.
I'd agree that $200 is too steep. But for $50, I could find a lot of uses for these!