Dozens of wireless chips and modules are available for building wireless devices for the industrial-scientific-medical (ISM) bands. The easyRadio Advanced (eRA) modules from LPRS provide some features that greatly improve design flexibility and performance (see the figure).
The modules operate in the 402- to 470-MHz or 802- to 940-MHz ranges. The modulation is either amplitude shift keying (ASK) or Gaussian frequency shift keying (GFSK). Up to 132 channels are available with channel spacing/signal bandwidth selectable from 12.5 to 150 kHz. Standard UART data rates are software selectable from 2400 to 115,200 bits/s.
The transmission protocol is the easy-Radio protocol, which uses 16-bit encryption and anti-crosstalk software. A raw data mode permits more flexibility to use custom coding systems on any available frequency, enabling direct compatibility with other ISM data modules from any manufacturer. Four separate data buffers improve throughput up to 25% over previous versions.
A constant alive digital received signal strength indicator (RSSI) eliminates the need for the host processor to provide analog-to-digital conversion. The modules also provide the last packet RSSI and the RSSI value delivered in the packet. A carrier detect pin replaces the former analog RSSI output signal.
An on-chip temperature sensor provides automatic temperature compensation to the frequency synthesizer oscillator, which is an important consideration in very narrow channel spacing. The frequency variation is less than ±1 kHz from –40°C to 85°C. The temperature value also can be read via a command that makes it available as a temperature measurement output to the application.
The eRA modules come in several configurations. The ERA400TRS and ERA900TRS are full transceivers for the 400- and 900-MHz bands, respectively. Transmit-only versions like the ERA400TS and ERA900TS are also available for the same frequency bands. Transmit output power is 10 dBm maximum on the 400-MHz modules and 5 dBm maximum on the 900-MHz modules. Receive sensitivity is –117 dBm at 12.5-kHz channel spacing and –107 dBm at 100-kHz spacing. The modules operate from a supply voltage in the 2.5- to 5.5-V range. The RF input/output impedance is a standard 50 Ω, and any common λ/4 monopole or printed-circuit board (PCB) loop antenna can be used.
The eRA modules are available from stock for $45 each from Saelig Company Inc.