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Circuit Cellar's editorial team comprises professional engineers, technical editors, and digital media specialists. You can reach the Editorial Department at editorial@circuitcellar.com, @circuitcellar, and facebook.com/circuitcellar

Impedance Matching Matters (EE Tip #145)

RF designers, as well as more and more digital-oriented designers, are used to thinking about impedance matching. But it is very easy to forget it when you are designing a non-RF project. A non-matched circuit will generate power losses as well as nasty reflection phenomena. (Refer to my article, “TDR Experiments,” Circuit Cellar 225, 2009.)

Impedance matching must be managed at the schematic stage, for example, by adding provisional matching pads for all integrated antennas, which will enable you to correct a slightly mis-adapted antenna (see Figure 1).

Figure 1: Impedance matching requirements must be anticipated. In particular, any embedded antenna will surely need manual matching for optimal performance. If you forget to include some area for a matching network like this one on your PCB, you won’t achieve the best performance.

Figure 1: Impedance matching requirements must be anticipated. In particular, any embedded antenna will surely need manual matching for optimal performance. If you forget to include some area for a matching network like this one on your PCB, you won’t achieve the best performance.

Impedance matching is also a PCB design issue. As rule of thumb, you can’t avoid impedance-matched tracks when you are working with frequencies higher than the speed of light divided by 10 times the board size. A typical 10-cm board would translate to a cutoff frequency of 300 MHz. A digital designer would then say: “Cool, my clock is only 100 MHz. No problem!” But a 100-MHz square-ware clock or digital signal means harmonic frequencies in the gigahertz range, so it would be wise to show some concern.

The problem could also happen with very slow clocks when you’re using fast devices. Do you want an example? Last year, one of my colleagues developed a complex system with plenty of large and fast FPGAs. These chips were programmed through a common JTAG link and we ended up with nasty problems on the JTAG bus. We still had issues even when we slowed down the JTAG speed to 100 kHz. So, it couldn’t have been an impedance matching problem, right? Wrong. It was. Simply because the JTAG is managed by the FPGA with the same ultra-fast logic cells that manage your fast logic so with stratospheric skew rates which translated into very fast transitions on the JTAG lines. This generated ringing due to improper impedance matching, so there were false transitions on the bus. Such a problem was easy to solve once we pinpointed it, but we lost some days in between.—Robert Lacoste, CC25, 2013

 

DIY Network-Ready Polyphonic Music Controller

Hans Peter Portner’s Chimaera project is a touch-less, expressive, network-ready, polyphonic music controller released as open source hardware. It is a mixed analog/digital offspring of the Theremin. An array of analog, linear Hall effect sensors make up a continuous 2-D interaction space. The sensors are excited with Neodymium magnets worn on fingers.

Portner's Chimaera project

Portner’s Chimaera project

The device continuously tracks and interpolates position and vicinity of multiple present magnets along the sensor array to produce corresponding low-latency event signals. Those are encoded as Open Sound Control bundles and transmitted via UDP/TCP to a software synthesizer. The DSP unit is a mixed-signal board and handles sensor read out, event detection and host communication. It is based on an ARM Cortex M4 microcontroller in combination with WIZnet W5500 chip, which takes care of all low-level networking protocols via UDP/TCP.

First Prize — Chimaera: The Poly-Magneto-Phonic Theremin, Hans Peter Portner (Switzerland)

The poly-magneto-phonic Theremin

In his project write-up, Portner explains:

With its touch-less control (no friction), high update rates (2-4 kHz), its quasi-continuous spatial resolution and its low-latency (<1 ms), the Chimaera can react to most subtle motions instantaneously and allows for a highly dynamic and expressive play. Its open source design additionally gives the user all possibilities to further tune hardware and firmware to his or her needs. The Chimaera is network-oriented and configured with and communicated by Open Sound Control, which makes it straight-forward to integrate into any setup.

The hardware of the Chimaera consists of two types of printed circuit boards and an enclosure. Multiple sensor units are daisy-chained to form the sensor array and connected to a single digital signal processing (DSP) unit.

Sensor unit

Sensor unit

A single sensor unit consists of 16 linear hall-effect sensors spaced 5mm apart and routed to a single output through a 16:1 multiplexer which is switched by the DSP unit. Downstream the multiplexer, the analog signal runs through an amplification circuitry.

A modular hardware design consisting of identical sensor units and a single DSP unit embedded in a wooden case allows building devices with array sizes of 16-160 sensors.
A modular hardware design consisting of identical sensor units and a single DSP unit embedded in a wooden case allows building devices with array sizes of 16-160 sensors.

The DSP unit is a mixed-signal board and handles sensor read out, event detection and host communication. It is based on an STM32F303Cx ARM Cortex M4 microcontroller in combination with WIZnet W5500, a hardwired 100Mbit IPv4/PHY chip taking care of all low-level networking protocols via UDP/TCP. The board’s analog part features 10 analog inputs providing connection points for the sensor units, leading to a maximally possible array of 160 sensors. Those analog inputs connect directly to three in parallel running 12bit analog-to-digital converters.

Schematic of the DSP unit (STM32F303Cx part)

Schematic of the DSP unit (STM32F303Cx part)

Networking technology in a zero configuration setup has advantages in respect to long-distance transmission, operating system independence and inherent ability for network performances. We thus use the Open Sound Control (OSC) specification via UDP/TCP as low-level communication layer.

Schematic of the DSP unit (WIZnet W5500 part)

Schematic of the DSP unit (WIZnet W5500 part)

Portner’s project won First Prize in the WIZnet Connect the Magic 2014 Design Challenge. The entire project and its associated files are now available.

The 100% Creative Workspace

Bernard Hiew sure knows how to get the most of his Penang, Malaysia-based “humble” electrical engineering workspace. He turned the third room of his apartment into a complete innovation space that’s used for everything from engineering to 3-D printing to playing music to woodworking.

Hiew's workspace features component storage, a soldering station, power supply, and more

Hiew’s workspace features component storage, a soldering station, power supply, and more

Hiew noted:

I spend my most of my time here, my little humble workspace. This room is not a dedicated workshop at somewhere else but is in my house. Half of the room is my workspace … The other half of the room is the main table where we do most of office work and surfing. Recently my wife is working from home, so she is occupying this table most of the time.

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To the right of his main engineering space is a bookcase and additional shelving

Hiew proves that with a little planning and ingenuity, you can create a fully functional workspace complete with essential engineering equipment and tools. His space includes a soldering station, a PCB UV box, multimeter, power station, computer, book shelves, and even a couch for relaxing and playing music. He also makes great use of storage containers for his electrical components.

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The other side of the room is for relaxing, as well as playing music

Share your space! Circuit Cellar is interested in finding as many workspaces as possible and sharing them with the world. Click here to submit photos and information about your workspace. Write “workspace” in the subject line of the email, and include info such as where you’re located (city, country), the projects you build in your space, your tech interests, your occupation, and more. If you have an interesting space, we might feature it on CircuitCellar.com!

 

LTC2946 Wide-Range I2C Power, Charge, and Energy Monitor

Linear Technology Corp. recently introduced the LTC2946, which is a high- or low-side charge, power and energy monitor for DC supply rails in the 0-to-100-V range. According to Linear Technology’s release:

An integrated ±0.4% accurate, 12-bit ADC and external precision time base (crystal or clock) enables measurement accuracy better than ±0.6% for current and charge, and ±1% for power and energy. A ±5% accurate internal time base substitutes in the absence of an external one. All digital readings, including minimums and maximums of voltage, current and power, are stored in registers accessible by an I²C/SMBus interface. An alert output signals when measurements exceed configurable warning thresholds, relieving the host of burdensome polling for data. The LTC2946 provides access to all the necessary parameters to accurately assess and manage board level energy consumption. In addition its wide operating range makes it ideal for monitoring board energy consumption in blade servers, telecom, solar and industrial equipment, and advanced mezzanine cards (AMC).

Source: Linear Technology

Source: Linear Technology

The LTC2946′s features include

  • 0 to 100 V Monitoring Range; greater than 100 V with internal shunt regulator
  • 12-Bit ADC with Scan and Snapshot Modes
  • I²C/SMBus digital interface
  • Guaranteed Accuracy: ±0.4% for 12-bit voltage; ±0.6% for 12-bit current and 32-bit charge; and ±1% for 24-bit power and 32-bit energy
  • Internal ±5%, external or crystal time bases
  • Minimum and maximum value recorder
  • Bias Supply Range: 4 to 100 V, or 2.7 to 5.9 V
  • Alerts on exceeding warning thresholds
  • Split SDA eases optoisolation
  • Shutdown Mode with IQ < 40 µA
  • 16-pin MSOP and 4 mm × 3 mm DFN Packages

Source: Linear Technology

New RP6V2 Robot Kit

Global Specialties recently introduced a new RP6V2 Robot Kit with RC5 remote and battery charger. The C-programmable autonomous mobile robot system is accessible enough for students and electronics enthusiasts to use. It comes with several example programs and a large C function library.

Source: Global Specialties

Source: Global Specialties

Features:

  • Atmel ATmega32 8-bit RISC microcontroller with 8 MIPS and an 8-MHz clock
  • Delivered fully assembled (no soldering needed)
  • CD with software and 138-page manual
  • AVR-GCC and RobotLoader open-source software for use with Windows and Linux
  • Programmable in C
  • Receives IR codes in RC5 format from the included remote control
  • USB Interface for easy programming and communication
  • Modular I2C bus expansion system
  • Expansion boards may be stacked as needed
  • Sample C programs and large C function library
  • Powerful tank drive train can negotiate steep ramps and obstacles
  • Large payload capacity
  • Light, collision, speed and IR-obstacle sensors integrated
  • Two 7.2-V DC motors
  • 625 CPR encoder resolution for precise speed regulation
  • Six PCB expansion areas

Source: Global Specialties