Plans and Kits

On offer are a few unusual plans and "half-kits" that take you fairly deep into circuit design. You can order just a PCB if you wish. There's no shopping cart - just write to us, we'll explain what these are about, and then configure a suitable half-kit for you, providing you design assistance if you need it.

Universal Audio DSP Module

We love analog, but we do not hate DSP, though we do regret the fact that to get into DSP you seem to need SMD soldering skills and a lot of math. Well, not any more. Here is a Universal Audio DSP board for the DIYer. Based on the Analog Devices ADAU1701, this board has only through-hole components (except for the ADAU1701 itself)! It features stereo audio input and output, 4 pots that feed into aux ADC inputs buffered by a rail-to-rail quad op amp, and 4 general-purpose digital I/O inputs. An I2C EEPROM plugs into a 8DIP socket. The board accepts a standard 48-pin DIP socket so you can plug in the ADAU1701 after soldering it to an adapter (or we can provide it pre-soldered). Programming the EEPROM requires no special hardware or software - there are several simple schematics available on the web using which you can build an RS232-based programmer in minutes for under $5.

We chose this particular DSP chip for an important reason. It, and the associated development environment SigmaStudio, are targeted at those who want an easy migration path from analog designs. SigmaStudio requires no programming - just drag and drop prebuilt blocks such as "State Variable Filter" and there - you have a circuit in minutes which can either be implemented as a DSP platform or simulated using this board and then implemented as an analog platform!

The PCB measures about 4x2.2 inches.

Universal Filter Module

Active (crossover) filters are not a new idea, having been around for decades. However, if you are on the lookout for an all-analog filter that can work as an advanced test instrument by offering the ability to continuously vary the crossover frequency via a simple front panel potentiometer, the choices are limited. Furthermore, if you also want the flexibility to play around with different transfer functions and even try your own—again, by simply flipping a front panel rotary switch—your choices narrow down still further. These twin requirements led us to design a continuous-time active filter module, the Universal Filter Module, which is featured in the April 2011 issue of Linear Audio. The PCB measures about 10x3 inches.

Shown here is a 2-channel filter built with two UFMs.

Universal Simulated Floating Inductor

Inductors are the bugbear of audio design. They are unwieldy, difficult to get in close tolerances or with high Q-values; if high-valued, they are extremely nonlinear. Simulated inductors have been written about extensively, especially grounded ones, but practical designs for floating ones are hard to come by. This innovatively-designed universal floating simulated inductor makes use of standard op-amps wired as Howland Current Pumps. It is variable from 1mH to 10H and can deliver upto 1A RMS. Fits on a 4x4 inch custom Eurocard-sized PCB making it suitable for mounting onto a 3U subrack as shown. This allows you to build a bank of variable inductors for test, measurement and prototyping.

A short article on the idea behind the design of this simulated inductor appears in the Oct 6th 2011 Ideas for Design special issue of Electronic Design magazine, and online at Electronic Design.

Universal Nixie Counter Module

Here is something different. Want to make a nixie frequency counter or just a clock? One module does it all. With 3 small PCB switches, you can set this module to count in the following modes:

• From 00-99 (for a frequency counter or timer)
• From 00-60 (for the minutes or seconds section of a clock)
• From 00-23 (for the hours section of a clock in 24-hour mode)
• From 01-12 (for the hours section of a clock in 12-hour mode)

Going from a 2-digit counter to a 4 or 6-digit counter involves merely cascading multiple modules using the 6-pin connectors provided. This is a great kit to learn digital electronics because all this is achieved without any microcontrollers - just three ordinary logic ICs, apart from the nixie driver ICs. (Achieving the 01-12 count is not as simple as it seems!) Also available (not shown) is a control board that generates all the timing signals required to operate this module as a counter/timer or clock (including automatic battery changeover that uses a 1.5V cell to keep the clock running without display in the event of power failure). A bonus feature is a switch that allows you to freeze the clock display while the clock continues to run in the background - use it as an event memory or kitchen timer! The PCB measures about 1.7x4.3 inches.

Audua Speaker Workshop Measurement Jig

Here is a downloadable document that describes a simple jig for the free and powerful Audua Speaker Workshop measurement package. Measurement mode is governed most simply by one two way switch and one rotary switch. The two-way switch determines whether you are in impedance or in SPL mode. The rotary switch is used in impedance mode as follows:

• Position 1: Sound Card Input Impedance
• Position 2: Channel difference/acoustic measurement
• Position 3: Impedance measurement
• Position 4, 5: Calibration of "Series" and "Reference" resistors

PCBs and kits are currently not available for this jig.