Electronics Projects
From Taclug
This is a list of electronics projects I have in various stages of incompletion. Please expand this page if you have a projects you'd like to share.
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Kurt's Electronics Projects
Most of these are ideas I have come up with to find new uses for old computers. I plan to release my designs under the TAPR Open Hardware License (http://www.tapr.org/ohl.html). As I continue to work on them, I'll post the details here. Feedback on anything here is always welcome.
1-Wire and 64 Channel Latch Drive Bay Adapter
This is the heart of a number of control projects I have in mind (including the Linux automated brewery). A serial port to Dallas Semiconductor 1-Wire (http://www.maxim-ic.com/1-Wire.cfm?CMP=WP-7) adapter provides connectivity for 1-Wire and iButton products including temperature sensors, a/d (analog to digital) converters, data loggers, etc. I am using OWFS (http://www.owfs.org/) to interface with devices. A parallel port controls a 64 channel latch using the 8 i/o lines (6 address bits, 1 data bit, and 1 write enable bit). This is for output only (hey, you win some you lose some). I'm using Parashell (http://parashell.sourceforge.net/) to control it. The latch outputs are logic level, but can easily be used to control external devices such as triacs (or relays, if you must) to switch high power devices. The drive bay adapter is designed to use the PC power supply and provides power connections for external switches and 1-Wire devices. The number of devices it will power is only limited by the wattage of your power supply. This project is constructed from off the shelf parts and requires no hardware programming. Cost in electronic parts is under $20
An earlier version of this design resides in my garage (http://temp.brewfund.com/hackbox/) and is controlling a hot plate (via a 1-Wire switch and a triac). The data is logged and graphed by rrdtool (http://oss.oetiker.ch/rrdtool/). It has been up continuously since February. As though in response to creating this page, a few days later the computer in my garage ceased responding. Rather than spend any time messing with it, I just hit the reset button and it came back up just fine. Anyone wanna help me figure out what caused the crash? :D
This project is still in prototype phase.
Serial Port Switch
For those who have a rack of servers and see KVM as overkill, a serial console is one alternative. Without much effort, a system can be configured for the bootloader, kernel messages, and terminal login to all operate over a serial connection. Some motherboards can also be configured for BIOS messages and setup to work over serial. This device uses the same 64 channel latch described above to switch serial ports. Cost in electronic parts is around $25, though with connectors and cabling this might cost as much as $100.
This project is still in prototype phase.
Opto-isolated AC Switch
This isn't really my design, just my implementation of a very common and underappreciated circuit. It utilizes a small current to operate a triac output opto-isolator (http://en.wikipedia.org/wiki/Opto-isolator). The output of the opto-isolator utilizes a slightly higher (though still small) current from the line being switched in order to actuate a larger triac (http://en.wikipedia.org/wiki/TRIAC) that can handle the desired current (up to 12 amps, in this case). This type of switching device is only effective to switch alternating current (http://en.wikipedia.org/wiki/Alternating_current). Once triggered, a triac will continue conducting until the current stops flowing. In a 60Hz AC wave, this happens 120 times per second – every time the voltage crosses zero. If you tried to use a triac to switch DC, the only way to turn it off would be to open the circuit. Aside from that, it's very simple to switch DC using transistors.
Forget about clunky, power hungry relays. Go solid state!
I built the prototype in a gutted X10 appliance controller. It is switched via 1-Wire, but could just as easily be switched by my 64 channel latch, a microcontroller, or directly from a parallel port. It's completely silent, it isn't susceptible to contact failure, and it takes as little as 5mA (a little more, when status LEDs are added) as opposed to the 100mA or more required to operate a typical relay. Let me put that in perspective for you – if you put one of these on every single output of the 64 channel latch:
5mA × 5V × 64 = 1.6 Watts
The electronic parts cost around $3.
This project is still in prototype phase.
Access Control/Keyless Entry/Security System
I originally had this idea when I lived at the former Geekpad. Every time a roommate moved out and didn't return his key, I was forced to rekey all the locks. How convenient would it be if I could just remove their access code from a database? But why stop there? Why not make it a full fledged security system? If you add a voice modem, you could even have it call you if there's a perimeter breach and tell you which sensor was triggered (screw paying a monthly "monitoring fee"). Even without a modem, you could have it send a SMS to your cell phone. I would hesitate to have it actually call the police....
Using 3 of the i/o pins and 4 status pins (input only) of a PC parallel port, along with a handful of small components, one could easily interface an inexpensive 12 key number pad. That leaves 5 i/o pins to operate electric strike plates, connect to motion detectors, magnetic door switches, home wiring tamper detectors, etc. If additional i/o is desired, a microcontroller could be employed (did someone say Arduino (http://www.arduino.cc/)?). If you wanted to get really fancy (and expensive) you could add RFID. Just walk up to your door, and it unlocks!
How cool would it be if your in-laws came to town to visit on a weekday and you didn't want to leave work to greet them, so you just let them in from the office?
This project is still in concept phase.
Power Monitor
Using a hall effect (http://en.wikipedia.org/wiki/Hall_effect) transducer, the current traveling through a wire can be translated to a voltage which can be read by a 1-Wire a/d converter (see above) or a capable microprocessor (did someone say Arduino (http://www.arduino.cc/)?). I gutted a 6 outlet surge suppressor and put 4 current sensors inside it. Cost in parts should be around $20-$30 (for the 4 channel 1-Wire version), but I'm still working the bugs out.
This project is still in prototype phase.
Linux CNC
This has been a dream of mine for years. Using EMC (http://www.linuxcnc.org/), stepper motors, and a little ingenuity, one could convert a conventional milling machine to a CNC (http://en.wikipedia.org/wiki/CNC) machine, or even build a whole machine from scratch! I believe I've designed a stepper motor driver that would do everything an average user would need, and would cost a lot less than the proprietary hardware available.
This project is still in design phase.
1-wire to powerline adapter
Turn your entire house into a low speed communication grid! Interfere with neighbors TV/radio/phone/etc. (maybe)! Sounds like fun!
This project is still in concept phase.
Hydrogen Generator
Okay, so it's not Linux related, and not EXACTLY electronics related, but it does use electricity! A lot of the supplies can be found at Home Depot. One could generate hydrogen from line power (the easy way out) or hook it up to a solar/wind generator (the green way). Pumps and storage tanks might be expensive...
Next step, the hydrogen powered car!! :D
This project is still in design phase.
Anyone else?
Please feel free to add your ideas here.
