StarBright User Manual
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13
Circuit Description
The StarBright meter has two circuit boards: the Analog Module with the analog signal processing
circuitry, and the Processor Board with the power supplies and user interface components.
Topics include:
13.1
Analog Module
13.1.1
Analog Circuit
The signal from the detector sensor enters the analog circuit and passes through EMI protection
components to a differential trans-impedance preamplifier. From there it is further amplified by a
programmable gain voltage amplifier and passes to an Analog-to-Digital (A/D) converter. All
calibration data for the analog circuit is stored in a memory chip on the main board. There are no
mechanical adjustable components (trimmers, and so on) in the StarBright. The Analog Module’s
on board digital processor receives data from the A/D converter and translates it into a
measurement of current in Amps. When used with Thermopile sensors, the data is then processed
by a sophisticated digital filter that speeds up the effective response time of the sensor and rejects
noise.
13.1.2
Fast Analog Input
In addition to the above basic analog circuit, the StarBright contains a second fast analog input.
This supports certain Ophir sensors that read energy pulses at higher rates than can be supported
by the basic analog circuit, but provides less overall accuracy than the above circuit. The fast
analog input consists of an EMI filtered voltage input that is passed to a first stage of mild voltage
attenuation. This is then passed to a fast A/D converter. Calibration data is stored on the same
memory chip mentioned above. The Analog Module’s on board digital processor receives data
from the fast A/D converter and translates it into a measurement that can be processed as
necessary.
13.1.3
Analog Output
The analog output is driven through an impedance of 100 ohms and provided as a means of
integrating the StarBright meter with other instruments (such as an oscilloscope)
13.2
Processor Board
The Processor Board is built around a Freescale i.MX283 ARM9 application processor. The digital
circuit includes an upgradeable FLASH chip that can be programmed in
13.2.1
Power Supply
The power supply provides the internal DC supply voltages for both the Processor Board and the
Analog Module. It also contains the battery charging circuit and the AC supply for the backlight.
The power supply circuits consist of high efficiency switch-mode designs.
