Technical Manual
Table Of Contents
- 1. Introduction
- 2. Hardware
- 3. The A431 Radio Module
- 3.1. About the A431 Radio Module
- 3.2. Functional description
- 3.3. Manufacturing Issues
- 3.3.1. Marking and labeling issues
- 3.3.2. Alignment Range and Switching Range
- 3.3.3. Tuning Procedure
- 3.3.4. Setting Up the Default Parameters
- 3.3.5. Definitions
- 3.3.6. Test Equipment Settings
- 3.3.7. Trimming Elements
- 3.3.8. Adjusting the Receiver Front End
- 3.3.9. Adjusting the VCOs
- 3.3.10. Adjusting the Crystal Reference
- 3.3.11. Checking the Receiver Parameters
- 3.3.12. Checking the Transmitter Parameters
- 3.3.13. Data Transfer Check
- 3.4. PCB Parts Placement
- 3.6. Frequency Reference Specifications
- 3.7. A431 Module’s Photographs
- 4. Software
11
The Microcontroller and the Power Management Sections
The radio unit is controlled via the SPI bus (to set the PLL chip parameters) and via
several ports of the microcontroller for such operations as transmit and receive. In
addition, the high current 5 volt LDO voltage source (U4) is switched on before the
radio module’s PA must be activated.The modem’s output (implemented in soft-
ware) is available on PB5 (
TXDI
), while the receiver output is fed to PD4 (
RXDO
).
The A/D subsystem is used to sample the inputs (ADC0 to ADC5); the 6th and 7th
analog input are used for on-board measurements as local battery, internal temper-
ature and
RSSI/PO
signal; the battery and temperature voltages are switched by
means of the analog switch U19. A stable 2.5 Volt reference supplied by U8 is ap-
plied to the A
ref
pin. The reference is powered by the microcontroller only when
sampling the A/D inputs. The external sensors are powered through U17. In order
to enlarge the maximum number of sensors sampled, several analog multiplexers
are used (U3/U7/U10). After sampling the A/D once, the software switches the mul-
tiplexers (using the signal
MUX
, pin PD2) and samples the inputs once again, thus
doubling to 12 the maximum number of analog inputs.
The sampled input values are stored in a FIFO memory based on a serial EEPROM
chip, U18. These values may be retrieved when a request is received over radio, or
over the serial line. The configuration parameters (e.g. the serial number of the de-
vice, the operating frequency, etc.) are stored in the microcontroller’s on-chip EE-
PROM.
The pulse counter functionality is implemented by means of the four interrupt inputs
INT4 to INT7 of the ATMega 103 microcontroller.
The power management supervises the charge/discharge of the battery (via Q1 and
half of U15), senses when it reaches the “misery” state and switches off the unit in
order to protect the battery (second half of U15). In addition, the software senses the
unit’s idle state (e.g. the unit is in a warehouse in storage condition), where no activ-
ities must be performed thus driving the unit into hibernation. If the unit is switched
off due to an extremely low battery level, Q2 would start it up again only if external
power is applied to the power connector (e.g. from a solar panel).
The terminal mode is implemented by means of the built-in UART. No on-board lev-
el drivers are present in order to minimize power consumption; a special adapter ca-
ble that performs the CMOS to RS232 level shift is available. By means of this cable
and using the implemented commands, various parameters can be changed/config-
ured.
A brown-out supervisor chip (U14) is used to assure a smooth start-up of the micro-
controller and avoid possible erratic behavior when the battery level descends be-
low the minimum operating value (2.7 volts). The same chip activates the write-
protect signal of the serial EEPROM during reset, in order to protect the data in the
EEPROM.