Small 12x56mm TTL - RS485 module (fits in a shrinktube, requires 5V, appr 10mA when idle but 90mA when transmitting or more if the bus is short circuited, around 250mA at extremes) to connect 1 to 4 TTL-serial devices to RS485 bus with automatic direction control and 120 Ohm termination (termination resistor can be unsoldered if desired).
1 master, OR 1..4 slaves can be connected to the RS485 bus.
Self echo is NOT heard, so slaves on same v485a will NOT hear each other (this saves some interrupt/processing, and power consumption in each slave).
RS485 master needs it's own v485a circuit: 1 master + 0 slave for that v485a. (of course, multiple v485a can be connected to same RS485 bus: upto 31, if termination resistor needs to be removed from all but the 2 devices at the end of the bus). Typically the master is at one end, and 1.. 4 slaves are at the other end of the bus (In Total, upto 121 devices can be connected to the bus with 31 v485a, more than what is actually practical).
It is recommended that the TTL devices (AVR, arduino, STM32, Orange-PI, Raspberry-PI or other SBC or development boards) connected to same v485a are physically close to each other, share the same GND, connected with short wires, and are powered simultaneously (eg. from same power supply as the 5V for the v485a circuit), although in practice (refer to your own field tests) some powered and others not might work(without locking the bus or preventing communications of the "neighbors").
Automatic direction control works reliably (important for some crippled protocols like MODBUS-RTU that does not allow preamble) even for 230..460 kbaud (upto max 960kbaud in lab-tests, careful application design and testing is needed if pushing the limits; only 1 device on each v485a allows >1Mbaud, especially with SP3485 chip, but this is rarely needed). Min 3 msec silence is recommended before starting TX on the bus (if such software/firmware setting exist, next to RS485 address settings).
