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| | | FM 433 Radio Modem | | | The FM 433 radio modem is a small multichannel transceiver for digital radio data transmission in the licence-free 433 MHz ISM band. The RF interface has a SMA socket for connecting a ¥ë/4 flag pole antenna (50 §Ù impedance). It should be noted that the device may only be used with a ¥ë/4 antenna with a connection that fits the antenna socket. Other antennas, especially antennas with greater antenna gain may not be connected for technical radio licensing reasons.
The FM 433 modem is controlled via an RS232 interface with TTL level. This modem¡¯s module character enables the user to incorporate it in existing devices or devices being designed with little effort. It is official radio approval in accordance with the R&TTE guideline and can therefore be used in almost all EU countries and those countries that have signed up to the R&TTE guideline agreement without having to be registered. In accordance with this guideline a duty cycle of maximum 10% is approved. Although the FM 433 does have an implemented duty cycle limitation the user must ensure that the transmission time of his application does not exceed this value. Before the FM 433 can be used the user is instructed to ascertain that it fulfils all the valid approval regulations of the countries it will be used in.
Application Examples
Due to the above features of this radio modem, applications on any areas of mobile data collection are possible:
Logistics
 Acquisition of stock changes
Stock taking
Gastronomy
Teleordering
Confirmatory information
Electronic Cash
Radio transmission from cash terminals to the central computer
Higher flexibility of cash terminals
Mobile Measuring Technology
No reading off on site, no manual entries
Difficult-to-reach measuring points are accessible
Safety Equipment
Components of alarm systems
Industrial Control Systems
Substitution of cablings for plant control systems
Plant state monitoring
and many more...
Functional Description
The FM 433 radio modem should be connected to a TTL level serial interface port and to the power supply. The basic condition after switching on the power supply is receiving in normal mode on the last channel set. Received data is then output straight afterwards and finished off with "block end signals". A maximum of 63 data bytes can be sent off in one block. Some system settings can be changed via the appropriate commands.
The modem can be set to a so-called transparent mode that enables data transfer across the complete signal range. No system commands are possible thereby. Incoming characters are sent off automatically. In order to leave the transparent mode the operating voltage has to be switched off. After it is switched back on the modem is in normal mode once again. All characters coming in via UART is transmitted out as soon as possible. No ETX is necessary. If the transmission limit is exceeded the transmission is made later. Any further signals coming that would lead to buffer overflow are not accepted for as long as this is the case (RTS is set). A different protocol is used on the radio interface that is not compatible with the one used in normal mode. Thus both modems have to be brought into transparent mode in order to set up a data transmission.
28 channels are available in the frequency range from 433.25 to 434.60 MHz in the 50-kHz grid for data transmission. For addressing and repeat algorithms, the user himself is responsible.
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