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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

Dev Platform with 2-D Multi-Touch and 3-D Gestures

Microchip Technology recently announced the availability of the 3DTouchPad, which it describes as “a PC peripheral and world’s first Development Platform for 2D multi-touch and 3D gestures.”Microchip_3DTOUCH_7x5_RGB

The 3DTouchPad adds free space gesture recognition to projected-capacitive multi-touch.  Basically, it provides 3-D gesture recognition via Microchip Technology’s GestIC, which provides a detection range of up to 10 cm for 3D gestures, as well as Microchip’s projected-capacitive 2-D multi-touch solution supporting up to 10 touch points and multi-finger surface gestures. Microchip also claims the 2-D multi-touch is enhanced by its new capacitive touch-screen line driver, MTCH652.

The new 3DTouchPad includes: a driverless, out-of-the-box features for Windows7/8.X and OS X, 3D air gestures; advanced multi-touch performance including surface gestures; and a free downloadable GUI and SDK/API package. Possible applications include home automation, remote controls, game controllers, and wearable devices.

The 3DTouchPad costs $99.

Source: Microchip Technology

Ultra-Low-Power 10-Bit Hall Encoder

iC-Haus’s iC-TW11 is an ultra-low-power, single-chip Hall encoder that enables energy-saving 10-bit angle detection. As a result, it is a good solution for battery-buffered applications.

iC-Haus TW11 encoder

iC-Haus iC-TW11 encoder

The encoder’s sampling rate of 10 Hz yields an average current consumption of typically 3 µA. In Standby mode between measuring cycles, the idle current cuts back to approximately 100 nA. In normal operation, the encoder supports sampling rates of 4 kHz with an activated filter and automatic amplifier gain for 10-bit resolution at maximum accuracy. A measuring cycle operates via either a SPI or a separate trigger input by an external event.

The  iC-TW11 EVAL TW11_1C evaluation board comes with a USB interface and GUI software. At a voltage supply of 3.3 V (+/-10 %), the iC-TW11 operates in an extended industrial operating temperature range from –40° to +125°C.

Production volume pricing starts at $4.21 in 1,000-piece quantities.

Source: iC-Haus



Linear Battery Charger with Multi-Chemistry Operation

Linear Technology Corp. recently introduced the LTC4079, which is a 60-V, constant-current/constant-voltage, 250-mA multi-chemistry battery charger. According to Linear, its “low quiescent current linear topology offers a simple inductorless design and accepts a wide 2.7 V to 60 V input voltage range.”LinearLTC4079


The LTC4079′s features, characteristics, and capabilities include:

  • A resistor-programmable 1.2- to 60-V battery charge voltage range with ±0.5% charge voltage accuracy
  • Adjustable charge current from 10 to 250 mA with an external resistor
  • A low-profile (0.75 mm) 10-pin 3 mm x 3 mm DFN package with backside metal pad for excellent thermal performance.
  • Guaranteed foperation from –40°C to 125°C in both E-and I-grades.
  • One thousand-piece pricing starts at $2.35 each for the E-grade.

Source: Linear Technology

Read Your Technical Documentation (EE Tip #145)

Last year we had a problem that showed up only after we started making the product in 1,000-piece runs. The problem was that some builds of the system took a very long time to power up. We had built about 10 prototypes, tested the design over thousands of power ups, and it tested just fine (thanks to POC-IT). Then the 1,000-piece run uncovered about a half-dozen units that had variable power-up times—ranging from a few seconds to more than an hour! Replacing the watchdog chip that controlled the RESET line to an ARM9 processor fixed the problem.

But why did these half dozen fail?

Many hours into the analysis we discovered that the RESET line out of the watchdog chip on the failed units would pulse but stay low for long periods of time. A shot of cold air instantly caused the chip to release the RESET. Was it a faulty chip lot? Nope. Upon a closer read of the documentation, we found that you cannot have a pull-up resister on the RESET line. For years we always had pull-ups on RESET lines. We’d missed that in the documentation.

Like it or not, we have to pour over the documentation of the chips and software library calls we use. We have to digest the content carefully. We cannot rely on what is intuitive.

Finally, and this is much more necessary than in years past, we have to pour over the errata sheets. And we need to do it before we commit the design. A number of years ago, a customer designed a major new product line around an Atmel ARM9. This ARM9 had the capability of directly addressing NOR memory up to 128 MB. Except for the fact that the errata said that due to a bug it could only address 16 MB. Ouch! Later we had problems with the I2C bus in the same chip. At times, the bus would lock up and nothing except a power cycle would unlock it. Enter the errata. Under some unmentioned conditions the I2C state machine can lock up. Ouch! In this case, we were able to use a bit-bang algorithm rather than the built-in I2C—but obviously at the cost of money, scheduling, and real time.—Bob Japenga, CC25, 2013

Arduino-Based Tube Stereo Preamp Project

If you happen to be electrical engineer as well as an audiophile, you’re in luck. With an Arduino, some typical components, and a little knowhow, you can build DIY tube stereo preamplifier design.

Shannon Parks—owner of Mahomet, IL-based Parks Audio—designed his “Budgie” preamp after reading an article about Arduino while he was thinking about refurbishing a classic Dynaco PAS-3.

Budgie preamp (Source: S. Parks)

Budgie preamp (Source: S. Parks)

In a recent audioXpress article about the project, Parks noted:

Over the last 10 years, I have built many tube power amplifiers but I had never built a tube preamplifier. The source switching seemed particularly daunting. A friend recommended that I refurbish a classic Dynaco PAS-3 which has been a popular choice with many upgrade kit suppliers. Unfortunately, the main part of these older designs is a clumsy rotary selector switch, not to mention the noisy potentiometers and slide switches. In the 1980s, commercial stereo preamplifiers started using IC microcontrollers that permitted cleaner designs with push-button control, relays for signal switching, and a wireless remote. While reading an article about the Arduino last year, I realized these modern features could easily be incorporated into a DIY preamplifier design.

All the circuits are on one custom PCB along with the power supply and microcontroller (Source: S. Parks)

All the circuits are on one custom PCB along with the power supply and microcontroller (Source: S. Parks)

Parks said the Arduino made sense for a few key reasons:

I found these features were incredibly useful:

  • A bank of relays could switch between the four stereo inputs as well as control mute, standby, gain, and bass boost settings.
  • A red power LED could use PWM to indicate if the preamplifier is muted or in standby.
  • An IR receiver with a remote could control a motor-driven volume potentiometer, change the source input selection, and turn the unit on/off. Any IR remote could be used with a code learning mode.
  • A backlit display could easily show all the settings at a glance.
  • Momentary push buttons could select the input device, bass boost, gain, and mute settings.
  • Instead of using several Arduino shields wired to an Arduino board, all the circuits could fit on one custom PCB along with the power supply and the microcontroller.

Parks used an Arduino Nano, which 0.73” × 1.70”. “The tiny Nano can be embedded using a 32-pin dual in-line package (DIP) socket, which cleans up the design. It can be programmed in-circuit and be removed and easily replaced,” he noted.

Parks used an Arduino Nano for the preamp project (Source: S. Parks)

Parks used an Arduino Nano for the preamp project (Source: S. Parks)

Parks described the shift register circuit:

The Budgie preamplifier uses a serial-in, parallel-out (SIPO) shift register to drive a bank of relays ….

A SIPO shift register is used to drive a bank of relays (Source: S. Parks)

A SIPO shift register is used to drive a bank of relays (Source: S. Parks)

Only four Arduino digital outputs—enable, clock, latch, and data—are needed to control eight DPDT relays. These correspond to the four outputs labeled D3, D4, D5, and D7 s …. The Texas Instruments TPIC6C595 shift register used in this project has heavy-duty field-effect transistor (FET) outputs that can handle voltages higher than logic levels. This is necessary for operating the 24-V relays. It also acts as a protective buffer between the Arduino and the relays.

Here you see the how to set up the Arduino Nano, LCD, power supply, push button , IR and motor control circuits (Source: S. Parks)

Here you see the how to set up the Arduino Nano, LCD, power supply, push button , IR and motor control circuits (Source: S. Parks)

As for the audio circuit, Parks explained:

The 12B4 triode was originally designed to be used in televisions as a vertical deflection amplifier. New-old-stock (NOS) 12B4s still exist. They can be purchased from most US tube resellers. However, a European equivalent doesn’t exist. The 12B4 works well in preamplifiers as a one-tube solution, having both high input impedance and low output impedance, without need for an output transformer. An audio circuit can then be distilled down to a simple circuit with few parts consisting of a volume potentiometer and a grounded cathode gain stage.
The 12B4 has about 23-dB gain, which is more than is needed. This extra gain is used as feedback to the grid, in what is often referred to as an anode follower circuit. The noise, distortion, and output impedance are reduced (see Figure 3). Using relays controlled by the Arduino enables switching between two feedback amounts for adjustable gain. For this preamplifier, I chose 0- and 6-dB overall gain. A second relay enables a bass boost with a series capacitor.
You only need a lightweight 15-to-20-V plate voltage to operate the 12B4s at 5 mA. Linearity is very good due to the small signal levels involved, as rarely will the output be greater than 2 VPP. A constant current source (CCS) active load is used with the 12B4s instead of a traditional plate resistor. This maximizes the possible output voltage swing before clipping. For example, a 12B4 biased at 5-mA plate current with a 20-kΩ plate resistor would drop 100 V and would then require a 120-V supply voltage or higher. Conversely, the CCS will only drop about 2 V. Its naturally high impedance also improves the tube’s gain and linearity while providing high levels of power supply noise rejection.

This article first appeared in Circuit Cellar’s sister publication, audioXpress (July 2014).