Vol. 29 Issue 3 Reviews
Electrotap Teabox Sensor Interface

T100A Teabox Sensor Interface, US$ 425; available from Electrotap, LLC, 606-A East Street, Parkville, Missouri 64152, USA; Web www.electrotap.com/.

Reviewed by Barry Moon
Wells, Somerset, UK

Electrotap is a company formed by Tim Place and Jesse Allison. In addition to marketing Tim’s ever-popular Tap.Tools externals for Max/MSP/Jitter and the Jade software, Electrotap now sell a hardware sensor interface called Teabox. Apparently, the box got its name from an early incarnation that used a tea box to contain the electronic circuitry. The first thing you notice about the Teabox is the rugged chassis design (see Figure 1).Figure 1 You can probably jump up and down on the thing and it wouldn’t break. Although it looks very rugged, you might be disappointed, or relieved, to discover how light it actually is.

The unique feature of the Teabox is that, unlike other budget priced interfaces that convert sensor voltages to MIDI, it converts voltages to digital audio data in the form of S/PDIF. There are several advantages to this, including speed, low latency, and resolution. Here are some figures published by the folks at Electrotap, supplemented by my own research:

  MIDI Teabox Teleo Kroonde Gamma
Number of times data is updated per second 43.47 Hz 4,000 Hz 100-1,000 Hz 59-200 Hz
Minimum latency for any given sensor 23.04 ms 1.71 ms ? 5-17 ms
Maximum resolution 7-bits (128 values) 12-bits (4096 values) 10-bits (1024 values) 10-bits (1024 values)
Price >US$ 149 US$ 425 US$ 189 US$ 1,495

Although the figures above make the Teabox look very impressive next to its competitors, there are some advantages to the Teleo and Kroonde Gamma systems: the Teleo system allows digital and PWM output, and the Kroonde Gamma is wireless. These are both areas of development that Electrotap is looking into for future versions of the Teabox.

The Teabox has both optical- and RCA-type connectors for making the S/PDIF connection to your audio interface. Most audio interfaces come with S/PDIF connectors, and I tried the Teabox on an Mbox, a Digi001, an RME Multiface, and a G5 (there is a use for that optical I/O after all!). In any one of these cases you need to set the clock source to sync to the Teabox. The only interface I didn't know how to set the clock source on was the G5, but I quickly found an OS X application called "Audio MIDI Setup" that allows you to configure the built-in hardware.

The Teabox is designed to handle up to 8 continuous sensor inputs and 16 digital “toggle” inputs. For the continuous inputs there are four XLR/TRS connectors and eight three pin (I-Cube style) connectors on the front, and two RJ-11 (telephone) connectors on the back (each carrying up to four sensor inputs). Also on the back of the box are the four RJ-11 connectors for the 16 digital inputs (again, each carrying up to four inputs). The use of XLR connectors is unique to the Teabox. Using the XLR format has several advantages, including sturdiness, availability, and the fact that the cables can be shielded to minimize electromagnetic interference. The only question I would have about using XLR is that if Electrotap does go wireless, the connectors are very heavy. As for the I-Cube connectors, I have always had a problem with them. Firstly, although standard connectors can be modified to work with them, they are very hard to find, and secondly, they do not lock on, and become easily disconnected. RJ-11 connectors have become something of a favorite with my students. They are easy to find, connect by locking in, and are light.

For operation in Max/MSP, the only software you need to use with the Teabox are two externals: teabox~ and teabox.bits~. teabox~ is connected to your adc~ input, outputting eight signals between 0 and 1 for the eight continuous inputs on the Teabox. The ninth outlet on teabox~ is routed through teabox.bits~ to provide 16 signals outputting 0s and 1s for the 16 digital inputs of the interface. The signals from teabox~ and teabox.bits~ are perfect for directly controlling signal processing, or they can be converted into messages using snapshot~ to perform control rate processing. The only downside to the Teabox using S/PDIF is that if you have an interface such as the Mbox or the G5 optical in, you will not be able to take in audio data at the same time.

For using the Teabox with other software, it comes with a TeaboxBridge application, designed to run using the free Max/MSP Runtime software (see Figure 2). Figure 2 TeaboxBridge converts audio coming from S/PDIF into either MIDI or OSC data. The MIDI can obviously be sent out a MIDI interface or bussed to other software internally. There are several options for how MIDI is generated, including note pitch or velocity, controller number or value, or pitch-bend. I crashed Pro Tools several times before I noticed there is also a “poll rate” control on each of the sensor conversions. Converting to OSC is just as simple, and in many ways more practical. Whether you convert to MIDI or OSC, the fact remains that the Teabox works far more successfully in Max/MSP than in any other software.

The Teabox option package I tested came with pressure and light sensors, and a knob (potentiometer). This option set costs US$ 100 over the price of the box alone. The first thing I noticed about the sensors that come shipped with the Teabox is how accurately they are calibrated, utilizing every last one of those 12-bits, although I am pretty sure the light sensor needs re-calibration for use in England (joke). I then tried a collection of I-Cube sensors that have been waiting around for connector changes to use in a different interface (my students having managed to kill two of the three I-Cubes owned by my university). I didn’t have to change the connectors for the Teabox, and again, the calibration was really good. The only I-Cube sensor that didn’t give the full range of output was the flex sensor. I then tried a homemade flex sensor I have used in Teleo and other systems, which is the same brand as the I-Cube version, and couldn’t get it to work at all in the Teabox. After this experience I was gladdened to find an article on the Electrotap Web site about calibrating sensors (www.electrotap.com/articles/opamps1.shtml). I also tried to use a simple oscillator circuit to test the digital input of the Teabox. Although I didn’t have the patience to make this work, I can at least say that the digital inputs work—when I touched the wires together I got the expected switch. One of the most impressive things about the Teabox is its ability to handle short circuits. When it gets a short, the box powers itself down, and comes back up a couple of seconds later.

In addition to the Teabox, Electrotap sells a wide variety of sensors, cables, and adapters for use with this interface.