Tech Forum Questions

Try the Insteon hub. It gives you smartphone and web access to your Insteon and X-10 modules at home or away, plus text alerts from sensors, if you install them. It’s a free app and there are no fees. Or, use the Smartlinc unit — an older version of the above — except no text alerts.

As a newbie myself, who has tried several approaches, I found one element left unsaid in the answers in the March issue.  It really matters what computing platform you use.  As a Mac user, I found it very hard to get going with the Parallax or Microchip solutions, since the development systems were extremely PC-centric, so I had to struggle with Boot Camp etc. or get a PC.  The Arduino and Atmel platforms were much easier, since the former supports the Mac thoroughly, and everything you could need for the latter can be found at http://www.obdev.at/products/crosspack.

I recommend the BASIC Stamp modules from Parallax because newcomers find them easy to use. In addition, Parallax has many books and manuals, as well as kits that get beginners off to a good start. I also like the Arduino Uno because of widespread support from users. The compatible Digilent chipKIT Uno32 provides a more powerful processor and will appeal to people who want to move beyond the eight-bit Atmel chip used in the original Arduino Uno. The kits mentioned use a 5V power source and work with 5V logic devices. Other boards — such as the ARM mbed and BeagleBone — operate from 5V, too, but the I/O pins provide 3.3V logic levels. You might find it difficult to breadboard with 3.3V logic chips, most of which come in surface-mount packages.

Hi. There are a number of ways to get started in mcu's.

In my opinion, Parallax has the best documentation to use for getting started with mcu's. If you do not want to buy their packages, you can download the pdf's and source the parts after looking at the components, which they provide in one nice place in their books. If you use a book such as the StampWorks book, then you should examine the schematics for their Professional Development Board (BS2 version and not the Propeller version) and buy the necessary components to build the experiments. Other BS2 versions are available such as the Stamp Stack II. The "What's a Microcontroller" pdf is also a good starting point.

All the concepts you learn with any mcu system will be able to be applied to any other mcu system. The syntax and instructions will vary but the concepts remain the same. Arduino has a number of books written about it and is probably the most popular among those who know little about mcu's. It was made with artists and builders in mind, not for engineers and tech-like people. They have done a good job of marketing and there are many applications made accessible through their "shield" format. Of course, there are quite a few books written about Arduino and you should examine whichever book to find out what parts you will need to work with the projects.

The PICAxe is also fairly popular and is programmed in a version of BASIC. The Propeller is supposed to be a little more advanced as are AVRs, PICs, and other major companies’ mcu's that are mostly programmed in C. For a beginner, I would stay away from the Propeller, AVRs, and PICs as there will probably be too steep a learning curve. The Basic Stamp 2 is a little more expensive as you will need the mcu and, if it is not a USB version, you will also need a USB-to-RS232 converter, unless you have a PC with the old serial port, DB9 style.

The Arduino is cheaper and more popular but you will most likely have to do a little more searching and trial and error to get your code running with the documentation available. Parallax, the company that makes the BS2, has very good documentation. Another advantage that the Arduino has, is that programs written in C/C++ will also work in the Arduino environment.

Books for the BS2: "What's a Microcontroller?" and "StampWorks."
Books for Arduino: the Evil Genius books and probably "Arduino Cookbook."
Books for the PICAxe: Unknown but there are bound to be some on the PICAxe homepage as well as Amazon.

Kits are available from many suppliers. Have a look online for some of these, but the list is not exhaustive: Parallax, Solarbotics, RobotShop, Digikey, ABRA Electronics, Sparkfun, Adafruit Industries, and Make. Be sure to check the websites thoroughly as some also have tutorials as well as documentation on their products.

Hi J.P.
I am also at a similar beginning stage as you describe. I am currently working through a book called "C Programming for Embedded Microcontrollers" by Warwick A. Smith, which I find thus far to be excellent. The ISBN is 978-0-905705-80-4.

Here are the books features: 

• Use only free or open source software.
• Learn how to download, set up and use free C programming tools.
• Start learning the C language to write simple PC programs before tackling embedded programming - No need to buy an embedded system right away!
• Start learning to program from the very first chapter with simple programs and slowly build from there.  No programming experience is necessary!
• Learn by doing - Type and run the example programs and exercises, which can be downloaded from the Internet. - A fun way to learn the C programming language.
• Ideal for electronic hobbyists, students and engineers wanting to learn the C programming language in an embedded environment on ARM microcontrollers.

As a beginner, I personally found Arduino to be the easiest platform to get a running start.

The maximum reverse voltage across the diode will be 36 volts. A conservative rule of thumb is to double that, so choose a diode with a rating of at least 72 volts. The maximum current will be whatever your PWM controller delivers to the motor. When the PWM controller shuts off at the end of each cycle, the voltage across the motor inductance will instantaneously reverse polarity and begin to flow through the diode. Using the same rule of thumb, pick a diode that is rated for twice this current. You also need to be sure the diode can dissipate the power while keeping its junction temperature below TJ max (150 deg C is typical). The power dissipated is 1/2 L I^2 (the energy stored in the motor inductance) multiplied by the frequency of your PWM controller. Depending on this result, you may need to put the diode on a heatsink. Once you know how much power you need to dissipate, check the diode data sheet to get the thermal resistance Rth(j-c) in degrees C/W. Multiplying your calculated watts by Rth tells you how much the junction temperature will rise above its case temperature. There will also be a rise from the case to whatever the case is mounted on (probably a heat sink) but this will be small so you can probably ignore it if you follow the diode manufacturer’s recommendations on how to mount the diode. There will also be a temperature rise of the heat sink above the ambient air. Calculate this using the heat sink data sheet and your calculated power dissipation. Add all of the temperature rises to whatever your maximum ambient temperature is expected to be and if this is less than Tj max, you are OK thermally.

I did an experiment a few months ago using a serial port as a light meter that can log brightness data to a file. I posted it at www.cedarlakeinstruments.com/blog/?p=10. The software I wrote to display data isn't online, but I can email it to you if you'd like. Just contact me at www.cedarlakeinstruments.com. Here is the posting:

The lowest cost way I could think of was to avoid a microcontroller or other logic component and use whatever was already on a modern PC. My idea was to use a Cadmium Sulphide (CdS) photocell. CdS cells are used in many camera light meters and work by changing resistance in response to ambient light. By using the current through a photocell to charge a capacitor, we can tell the light level by measuring the time taken to charge. In days of old, we could have used a joystick port to do this, but those are long gone, now replaced by USB-connected joysticks.

On PCs without joystick ports, we could have done the same thing with the printer port. However, those are also a thing of the past.

So far, most PCs still come with serial ports, so we'll try those. The Clear To Send (CTS) and Data Terminal Ready (DTR) lines can be controlled from a Win32 or .NET application. There is some concern about the responsiveness of Windows, but as long as we avoid very short time constants, we can get usable data.

The concept is to build an RC circuit from a photocell and a 200 mF capacitor. The photocell is driven from the DTR line, and the junction of the capacitor and photocell is read by the CTS input. Here's the schematic; it's pretty simple:

The results are surprisingly useful. Discharging the circuit for two seconds and then charging it while polling the CTS line every five milliseconds shows a clear difference as the photocell is pointed at various areas of a lighted room.

All you need is a small solar cell mounted in the end of a "toilet paper" tube. Make sure the cell's face faces inward and you seal the tube end containing the cell so it's (more or less) "light-proof".  If you wish, paint the inside of the tube FLAT BLACK before mounting the solar cell (reduce any "internal reflections, etc." of the tube).

To use: Connect the solar cell's leads to the DMM (polarity is not important: all you want is the "absolute" display value) and set the DMM to the 2V scale.  Darken the room and turn on the CFL you want to "measure".  Wait a few minutes to allow the bulb to fully "warm up" and point the open end of the tube at the glowing CFL.  The voltage reading on the DMM display will give you the "relative brightness" indication you're looking for (i.e., "higher" voltage reading = brighter lamp). IMPORTANT: Make sure you use the same "measuring distance" (i.e., 1 inch) between the open end of the tube and each CFL you're measuring for best accuracy! Repeat for all CFL's you want to measure.

Hope this helps.

Chances are the magnets are OK on your stylus, the problem is most likely with the coil system in the cartridge body. The coils are not to be magnetized, their job is to generate a voltage from the mechanical movement of the magnets on the stylus shank when playing a record. My experience with the AKG P8 is that it does not age well, so rather than fight a losing battle I suggest replacing it with something new. I just purchased a Shure M97xe and I have no complaints.

The Wand board will run Android and is very similar to the raspberry pi. www.wandboard.org

While it is not exactly a wall mounted product, the Arduino ADK (Android Development Kit) is built to interface with the Android platform. I hear that the Raspberry Pi is close to being able to run Android and that might be an interesting alternative.

Look at www.tubesandmore.com They have both local oscillator coils and i.f. transformers for am tube radios listed. P-C208B, P-C70-OSC, and P-C78 look like the ones.