ISM Basics (EE Tip #100)

The industrial, scientific, and medical (ISM) bands are radio frequency ranges freely available for industrial, scientific and medical applications, although there are also many devices aimed at private users that operate in these bands. ISM devices require only general type approval and no individual testing.

Source: Wolfgang Rudolph & Burkhard Kainka’s article, “ATM18 on the Air,” 080852, Elektor, 1/2009.

Source: Wolfgang Rudolph & Burkhard Kainka’s article, “ATM18 on the Air,” 080852, Elektor, 1/2009.

The radio communication sector of the International Telecommunication Union (ITUR) defines the ISM bands at an international level. Wi-Fi and Bluetooth operate in ISM bands, as do many radio headphones and remote cameras, although these are not usually described as ISM devices. These devices are responsible for considerable radio communications interference (especially at 433 MHz and at 2.4 GHz).

ITU-R defines the following bands, not all of which are available in every country:

  • 6.765 to 6.795 MHz
  • 13.553 to 13.567 MHz
  • 26.957 to 27.283 MHz
  • 40.66 to 40.70 MHz
  • 433.05 to 434.79 MHz
  • 902 to 928 MHz
  • 2.400 to 2.500 GHz
  • 5.725 to 5.875 GHz
  • 24 to 24.25 GHz

Some countries allocate further ISM bands in addition to those above. ISM applications have the lowest priority within any given band. Many bands available for ISM are shared with other spectrum users: for example the 433 MHz ISM band is shared with 70 cm amateur radio communications.

ISM users must not interfere with other users, but must be able to tolerate the interference to their own communications caused by higher-priority users in the same band. The band from 868 MHz to 870 MHz is often mistakenly characterized as an ISM band. It is nevertheless available to short-range radio devices, such as RFID tags, remote switches, remote alarm systems, and radio modules.

For more information, refer to Wolfgang Rudolph & Burkhard Kainka’s article, “ATM18 on the Air,” 080852, Elektor, 1/2009.

Issue 265: Embedded Systems Abound

I recently read on CNN.com the transcript of an interview (May 9, 2002) with arachnologist Norman Platnick who stated: “You’re probably within seven or eight feet of spider no matter where you are. The only place on earth that has no spiders at all—as far as we know—is Antarctica.” It didn’t take long for me to start thinking about embedded systems and my proximity to them. Is the average person always within several feet of embedded systems? Probably not. But what about 50% or 60% of the time? E-mail me your thoughts.

Circuit Cellar 265, August 2012 - Embedded Development

Embedded systems are becoming ubiquitous. They’re in vehicles, mobile electronics, toys, industrial applications, home appliances, and more. If you’re indoors, the temperature is likely monitored and controlled by an embedded system. When you’re engaged in outdoor activities (e.g., hiking, golfing, biking, or boating), you probably have a few MCU-controlled devices nearby, such as cell phones, rangefinders, pedometers, and navigation systems. This month we present articles about how embedded systems work, and our authors also provide valuable insight about topics ranging from concurrency to project development.

Freescale’s Mark Pedley kicks off the issue with a revealing article about a tilt-compensating electronic compass (p. 16). Now you can add an e-compass to your next MCU-based project.

E-compass technology (Source: M. Pedley, CC265)

Turn to page 24 for an in-depth interview with Italy-based engineer Guido Ottaviani. His fascination with electronics engineering, and robotics in particular, will inspire you.

Have you ever come across a product that you know you could have designed better? Scott Weber had that experience and then acted on his impulse to build a more effective system. He created an MCU-based light controller (p. 32).

The MCU-based light controller is on the right (Source: S. Weber, CC265)

If you want to ensure a microcontroller works efficiently within one of your systems, you should get to know it inside and out. Shlomo Engelberg examines the internal structure of an I/O pin with a pull-up resistor (p. 40).

Bob Japenga continues his series “Concurrency in Embedded Systems” on page 44. He covers atomicity and time of check to time of use (TOCTTOU).

On page 48 George Novacek presents the second part of his series on project development. He covers project milestones and design reviews.

Ed Nisley’s June 2012 article introduced the topic of MOSFET channel resistance. On page 52 he covers his Arduino-based MOSFET tester circuitry and provides test results.

The MOSFET tester PCB hides the Arduino that runs the control program and communicates through the USB cable on the left edge. (Source: E. Nisley, CC265)

If you read Robert Lacoste’s June 2012 article, you now understand the basics of frequency mixers. This month he presents high-level design methods and tools (p. 58).

Jeff Bachiochi wraps up the issue with an examination of a popular topic—energy harvesting (p. 68). He covers PV cell technology, maximum power point tracking (MPPT), and charge management control.

A great way to investigate MPPT for your design is to use an STMicroelectronics evaluation board, such as this STEVAL-ISV006V2 shown in the top of the photo. The smaller cell in the center is rated at 165 mW (0.55-V output at 0.3 A) measuring 1.5” × 0.75”. At the bottom is a Parallax commercial-quality solar cell that is rated at 2.65 W (0.534-V output at 5.34 A) measuring 125 mm. (Source: J. Bachiochi, CC265)

Circuit Cellar 265 is currently on newsstands.

Elektor RF & Microwave App for Android

Elektor has an iPhone/iPad app for several months. And now Android users can have an Elektor app of their own. The Elektor RF & Microwave Toolbox app is perfect for engineers and RF technicians who need easy, reliable access to essential equations, converters, calculators, and tools.

A screenshot of the Elektor RF & Microwave app for Android

The app includes the following handy tools:

1.Noise floor (Kelvin,dBm)
2.Amplifier cascade (NF, Gain, P1db, OIP2, OIP3)
3.Radar equation (2-way path loss)
4.Radio equation (1-way path loss)
5.Power and voltage converter (W,dBm,V,dBµV)
6.Field intensity and power density converter (W/m2, V/m, A/m, Tesla, Gauss,dBm, W)
7.Mismatch error limits (VSWR, Return loss)
8.Reflectometer (VSWR, Return loss)
9.Mitered Bend
10.Divider and Couplers (Wilkinson, Rat race, Branchline , microstrip and lumped)
11.Balanced and und balanced PI and T attenuator
12.Skin depth (DC and AC resistance)
13.PCB Trace calculator (impedance/dimensions)
14.Image rejection (amplitude and phase imbalance)
15.Mixer harmonics (up and down conversion)
16.Helical antenna
17.Peak to RMS (peak, RMS, average, CF)
18.Air Core Inductor Inductance
19.Parallel plate Capacitor
20.PI and T attenuator
21.Ohm’s Law
22.Parallel LCR impedance/resonance
23.Series LCR impedance/resonance
24.Inductor impedance
25.Capacitance impedance
26.Antenna temperature (Kelvin)
27.Radar Cross Section (RCS) calculator (Sphere,Cylinder, flat plate, corners, dBsm)
28.Noise Figure Y-Factor Method
29.EMC (EIRP, ERP, dBµV/m)
30.Noise figure converter (dB, linear, Kelvin)
31.Frequency Band Designations
32.Resistor color code (reverse lookup, 3 to 6 band)
33.Filter Design (Butterworth, Chebyshev, prototype):
34.µ-Filter Design (microstrip, stripline)
35.PCB Trace Width and Clearance Calculator

Visit the Android Market for more information about the Elektor app.

Circuit Cellar does not yet have an app for Android. The Circuit Cellar iPhone/iPad app is available on iTunes.

Screenshots of the Circuit Cellar app

Elektor International Media is the parent company of Circuit Cellar.

RFI Bypasssing

With GPS technology and audio radio interfaces on his personal fleet of bikes, Circuit Cellar columnist Ed Nisley’s family can communicate to each other while sending GPS location data via an automatic packet reporting system (APRS) network. In his February 2012 article, Ed describes a project for which he used a KG-UV3D radio interface rigged with SMD capacitors to suppress RF energy. He covers topics such as test-fixture measurements on isolated capacitors and bypassing beyond VHF.

Photo 2 from the Febuary article, "RFI Bypassing (Part 1)." A pair of axial-lead resistors isolate the tracking generator and spectrum analyzer from the components under test. The 47-Ω SMD resistor, standing upright just to the right of the resistor lead junction, forms an almost perfect terminator. (Source: Ed Nisley CC259)

Ed writes:

Repeatable and dependable measurements require a solid test fixture. Although the collection of parts in Photo 2 may look like a kludge, it’s an exemplar of the “ugly construction” technique that’s actually a good way to build RF circuits. “Some Thoughts on Breadboarding,” by Wes Hayword, W7ZOI, gives details and suggestions for constructing RF projects above a solid printed circuit board (PCB) ground plane.

You can read this article now in Circuit Cellar 259. If you aren’t a subscriber, you can purchase a copy of the issue here.