Barometers Realm

Key Specifications

Exterior

Shape and Housing

The housing has a distinctive streamlined shape of an inverted trapezoid with rounded corners: the wide upper part carrying the display tapers smoothly toward the bottom. The lower edge is concave, forming a convenient recess for the cord and the fingers. The housing itself is moulded from dark grey plastic with a soft matte finish.

Two light grey rubberized hand grips wrap around the sides of the housing. They protrude above the front and back surfaces, protect the instrument from impacts if dropped, and keep it from slipping out of the hand.

The back panel consists of two parts. The lower part, the battery compartment cover, is held by four screws. The upper part features a raised tab with slots. Inside the housing are two CR2032 battery holders, a RESET button for restoring factory settings, and a piezo sounder for audible signals, mounted on the inside of the back cover.

Display

Almost half of the front is taken up by a large monochrome segmented liquid crystal display in a glossy black frame with the HUGER logo below it. The display has no backlight. Thin lines divide the screen into three rows:

1. Top row — the main reading in large digits: atmospheric pressure in mb/hPa (or inHg), or altitude in metres or feet. On the left, a framed indicator shows the current mode, BARO or ALT.
2. Middle row — on the left, a bar graph of pressure or altitude change over 12 hours with a time scale , , , ; on the right, the weather forecast icons: two clouds of different sizes and a sun.

Controls

Below the display are five buttons grouped by function:

• BARO and ALT — two bright yellow buttons directly under the screen. They switch between the barometer and altimeter displays and serve as confirmation in setting modes.
• TIME — a wide grey button in the centre. It cycles through the bottom-row displays (time, date, alarm, stopwatch) and is used to set them.
• + / − — a grey twin rocker key. It changes values during setting, scrolls through the 12-hour history, clears memories, turns the alarm and altitude alarm on and off, switches units of measurement, and starts and stops the stopwatch.

Button combinations give access to service functions. Holding BARO + TIME together starts pressure calibration (CAL Po), ALT + TIME starts altitude calibration (CAL Hx), and holding + and − together switches units of measurement.

Protective Case

The instrument comes with a protective case made of faux leather with whipstitched edges. The front of the case is covered by a clear plastic window spanning the whole panel: all readings are visible through it, and the buttons can be pressed right through the film without taking the instrument out. The case protects the housing from scratches, dust and splashes. A braided black neck cord allows the instrument to be worn around the neck or attached to a rucksack.

Power

The instrument runs on two CR2032 lithium batteries. It has no power switch: the instrument is permanently switched on. This is the only way it can continuously measure pressure, keep the 12-hour history for the graph and forecast, and keep time. When the batteries run low, a BATT indicator appears on the display. The manufacturer recommends keeping the instrument in barometer mode when it stays at the same altitude for a long time, since altimeter mode, with its frequent sampling, drains the batteries faster. After a battery change the instrument starts with an empty memory, and the 12-hour graph fills in gradually as data accumulates.

Weather Forecast

The forecast follows the classic principle of barometric meteorology: what matters is not the absolute pressure but its change over time. In barometer mode the instrument measures pressure, stores the history and analyses the trend. Steadily rising pressure usually heralds improving weather, falling pressure deteriorating weather, and a sharp drop an approaching depression with precipitation.

The result is shown on the right of the display's middle row as one of four states, composed of stylised sun and cloud icons:

• Sunny
• Slightly Cloudy
• Cloudy
• Rainy

The manual adds several honest caveats to the forecast:

• the icon describes the expected weather for the next 12–24 hours within a radius of about 30–50 km, not the weather outside at the moment;
• the accuracy of a forecast based on pressure trends alone is about 70–75%;
• at night, the "sun" icon simply means clear weather.

Since the instrument cannot tell a pressure change caused by the weather from one caused by a change in altitude, a correct forecast is only possible when the instrument stays at a constant altitude in barometer mode.

Pressure and Altitude Graph

An interesting feature that works in both barometer and altimeter modes is the bar graph that the instrument constantly draws on the left of the display's middle row. It shows how pressure or altitude has changed over the past 12 hours.

• The horizontal axis covers the time from in steps, i.e. : −12, −10, −8, −6, −4, −2 and 0 h. The scale below the graph is labelled , , , ; the rightmost column corresponds to the present moment.

The graph is very clear: a single glance is enough to judge the barometric trend, which on classic dial barometers required a manually set reference needle and repeated observations. On a hike, the same graph in altimeter mode becomes a simplified profile of the route.

For exact figures there is a separate history display. The + / − keys scroll through pressure or altitude values in one-hour steps, back to 12 hours.

Barometric Sensor Design

In the Huger EB833, pressure is measured by a silicon piezoresistive absolute pressure sensor made by Motorola — a microelectromechanical (MEMS) device in which the sensing diaphragm and the measuring element are formed in a single silicon die. The sensor occupies the central position on the main board (board marking 016-810591-14, MB-EB833-1.4) and is the instrument's only primary transducer: the barometer, the altimeter and the weather forecast all depend on it.

In 2004 Motorola's semiconductor division was spun off as an independent company, Freescale Semiconductor.

The sensor is a custom (OEM) version made for the instrument's manufacturer, Huger. It converts absolute atmospheric pressure into a weak electrical signal. The instrument's electronics then amplify it, digitise it and convert it either into pressure (barometer mode, trend-based forecast) or into altitude above sea level (altimeter mode).

Construction

From the outside in, the sensor consists of the following parts.

1. Metal cap with a port. Through the central opening, ambient air reaches the working side of the die; Motorola calls it the pressure side (P1).
2. Silicone gel. A soft silicone gel fills the cavity above the die. It protects the die surface and the wire bonds from dust and moisture, yet, being virtually incompressible and compliant, transmits pressure to the diaphragm without distortion. This is the gel visible through the port.
3. Die coat — a thin protective layer over the active surface.
4. Silicon die a few millimetres in size. A cavity is anisotropically etched into its back side, and the remaining thin web of silicon forms the diaphragm. The X-ducer strain gauge is diffused into the diaphragm and connected to aluminium metallisation traces.
5. Constraint wafer and vacuum cavity. The die is bonded to a silicon constraint wafer through a glass frit layer; the bonding is done before dicing, at the level of whole wafers (wafer-to-wafer bonding). The cavity under the diaphragm is thereby hermetically sealed and evacuated: it serves as the vacuum reference, so the sensor measures absolute pressure, referenced to zero, rather than a difference from some external pressure.

Measuring Principle

The piezoresistive effect. The sensor is based on the piezoresistive effect: the resistivity of a semiconductor, above all single-crystal silicon, changes markedly under mechanical stress. In silicon this effect is tens of times stronger than in metal strain gauges. It should not be confused with the piezoelectric effect, in which deformation of a crystal (quartz, for example) generates an electric charge: a piezoresistor generates no charge, it only changes its resistance and therefore requires an external power supply.

How pressure becomes voltage. Ambient air presses on the diaphragm from above through the port and the gel layer; below it is vacuum. The diaphragm deflects in proportion to the absolute pressure, creating mechanical stresses in the silicon that peak near its edges. The strain gauge embedded in the diaphragm senses these stresses, and the sensor's output voltage changes almost perfectly linearly with pressure.

The classic layout: the Wheatstone bridge. Most piezoresistive sensors use four strain gauges arranged on the diaphragm so that two are stretched and two compressed. The resistors are connected in a Wheatstone bridge; without pressure the bridge is balanced, and the diaphragm's deflection unbalances it, producing a voltage across the bridge diagonal proportional to the pressure.

Motorola's solution: the X-ducer. Motorola used a different, patented design — a single strain gauge operating on transverse voltage and sensitive to shear stress in the diaphragm (silicon shear stress strain gauge). The element is X-shaped, hence the name X-ducer:

• the supply current is passed through one pair of opposite ends, with the current axis oriented at 45° to the diaphragm edge;
• two other points in the middle of the resistor serve as voltage taps;
• without pressure the taps are equipotential and the voltage between them is close to zero;
• when the diaphragm deflects, shear stress in the silicon deflects the current lines, and a transverse potential difference proportional to the pressure appears between the taps.

Geometrically this resembles a Hall sensor, with mechanical stress playing the role of the magnetic field. The element is placed near the midpoint of the diaphragm edge, where shear stress is greatest. Since the strain gauge is part of the diaphragm itself, errors from differing thermal expansion of the resistor and its substrate, typical of bonded strain gauges, are eliminated. Motorola also stressed another advantage: the behaviour of a single element is highly predictable, which simplifies compensation.

The Sensor at Work in the Instrument

Signal path. The components on the board point to a classic analogue signal-processing scheme typical of instruments from the second half of the 1990s:

1. The sensor delivers a differential signal on the order of tens of millivolts.
2. An amplifier raises it to a level suitable for analogue-to-digital conversion. Zero offset and gain were set at the factory with trimmer resistors: VR3 and a second one to the right of the sensor. Their wipers are sealed with red locking lacquer — the factory calibration seal.
3. Thermistor — the black bead on long leads at the top of the board. It measures temperature for the display and probably for correcting the sensor's temperature drift.
4. A microcontroller with an ADC digitises the signal, keeps the 12-hour history, computes the trend and forecast, and drives the LCD. It is clocked by the 2.45768 MHz crystal Y2, while the clock and calendar run on the 32.768 kHz watch crystal Y1.
5. The piezo sounder BZ1 produces the alarm and altitude alarm signals.

Barometer and altimeter — one sensor. The altimeter has no separate sensing element: altitude is calculated from the same absolute pressure using the barometric formula. Near sea level, climbing about 8 m lowers the pressure by 1 hPa. Two consequences follow:

• the altimeter's 1 m resolution corresponds to a pressure change of about 0.12 hPa, i.e. a sensor signal of around 7 µV — an extremely small quantity, so real-world accuracy is determined by the stability of the entire signal chain;
• the instrument cannot tell a pressure change caused by the weather from one caused by altitude: a 1 hPa change in the weather looks to the altimeter like a climb or descent of about 8 m. This is why the manual calls for periodic altitude calibration against known reference points.

Conclusion

The Huger EB833 is a characteristic representative of the generation of digital barometers of the late 1990s, when electronics finally moved out of laboratories and weather stations and into travellers' pockets. In a small housing weighing less than 100 grams, the instrument combines an altimeter with route memory, a barometer with a 12-hour history and trend graph, a weather forecast, a thermometer, a clock, a calendar, an alarm and a stopwatch. Only a decade earlier, such a set would have required several separate instruments.

Technically, the instrument is interesting above all for its heart — an early Motorola silicon MEMS sensor with a single-element X-ducer strain gauge. It is an analogue sensor without on-chip compensation, and its accuracy is ensured by external circuitry: factory trimmer adjustment, a thermistor and a microcontroller. In this way the EB833 captures an intermediate stage in the history of barometric sensors — between the mechanical aneroid and the fully digital modules with calibration stored in memory that in the following decades found their way into wristwatches and smartphones.

The well-thought-out ergonomics — rubberized side grips, a large three-row display, colour-coded buttons, a faux leather case with a clear window, and a neck cord — show that the instrument was designed as a reliable field tool rather than a souvenir. This surviving example, with its original 1997 sensor, the factory seals on its trimmer resistors and its original case, is a complete and representative specimen of the consumer measuring equipment of its time.