![]() ![]() ![]() It can also be connected to the RS-232 port of a device using the RS-232-serial converter. Similarly, RPi’s UART port can be connected to the USB interface of a device using a USB-serial board. For example, a device with the 5V TTL UART port can connect to RPi’s serial port of using a 5 to 3.3V TTL Logic Shifter. If the other device has a different UART voltage level, the suitable voltage level shift or serial adaptor must be used. ![]() Remember that RPi’s UART port is 3.3V and it should be connected with the compatible serial port. So, there are several sensor modules that can be interfaced with Raspberry Pi using its UART port. In fact, most of the sensor modules that are designed for peer communication with controllers/computers have the UART port for data communication. Most of the embedded devices have the UART port for exchanging console data. Things get a little wonky when you start to talk about voice calls, as there isn't a lot of standardization in how to get the audio channel in/out of linux on telephony devices yet, but ofono and telepathy seem to have made strides in that direction.In the previous tutorial, we learned how to use Raspberry Pi’s (RPi) serial hardware port for serial data communication over the universal asynchronous receiver/transmitter (UART) protocol. ![]() To further restrict access to telephony device capabilities you can break out ModemManager or oFono along with Polkit. In both cases, access to the SIM is limited to processes that can speak to the telephony device's control channel, and the data side is firewalled with iptables like any other network interface. On devices supporting "the new hotness", you get a special character device that speaks the MBIM or QMI protocols for a control channel, and an "ethernet" interface for IP traffic. Typically from the perspective of Linux, a "old and busted" telephony devices will appear as a TTY which a (relatively) privileged process can use as a control channel and/or to set up a PPP interface. I'm curious what you'd consider a GSM or SIM firewall to look like. ![]()
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