We tried to build an organic system so that whoever gets a TXtemp, TXsoil sensor or a bridge for RS232 or ModBus sensors and devices like TXdata can immediately use them without wasting time in configurations (and we also took the opportunity to insert some things into our system some "extra" not foreseen by the standards!). It is interesting to measure the humidity of the ground, but we have also thought about other things; and then we have TXtemp to measure the temperature (one of the uses of TXtemp is in association with SuperClock), and for practically any type of measurement we have TXdata (RS232, RS485 ModBus) - which can be connected to thousands of existing third-party professional RS232 or ModBus meters (and there is something for all needs: temperature and humidity meters, anemometers, voltage meters, energy, light meters, water meters, presence sensors, brightness sensors, soil humidity sensors, etc. ; practically all professional meters are available in ModBus or RS232 standard; and not just meters). We have also included the most widespread industrial standards, HTTP and MQTT, so that our elements can be used in any automation. It seems if there is a lot of RFI in the installation, shielded twisted cable can be justified.

If there are several sensors near and/or other data to be transmitted via GSM, it is more convenient to use Standard / RF versions supported on a concentrator or controller such as RXTXeasy GSM so you will be able to use one single SIM. Depends what you mean by a serial cable - Fibre, Ethernet, RS232, RS485, RS422, USB, HDMI, SMPTE292 are all examples of serial communications media. Rs485 is low impedance balanced , so twisting the pair helps with noise immunity as well as reducing the attenuation effect of higher baud rates due to the parallel capacitance of the wires in the cable jacket over the long lengths. Not only that, it can also be used to know if there is water in any place or not; for example, positioned appropriately, it can be used to know if a tank or a drinking trough is full or empty, or if a well has reached a certain level (eg to stop pumping water). There is a slight surcharge which covers PayPal fees.

Purchase by using the following button and adding to the PayPal cart (where you can change the quantity). 100% humidity, click the "humidity 100%" button and the reference will be stored. You can enter the data relating to the MQTT Broker you want to use; the name of the Topic to be used to control it and to read the periodic transmissions of the humidity percentage is shown. If handshaking is not necessary, an ordinary 4 wire telephone cable could be used, provided that the pins are cross-connected as shown in the picture below. For RS232a crossover cable is used where pin 1 is connected with pin 6 at the other connector, pin 2 with pin 5, etc. This interconnects the transmit and receive signals of both PLCs, and also the handshaking signals DTR and DSR. Therefore for RS485 communications no crossover cable is used. Otherwise a full 6 wire cable must be used. The normal way to implement this is with a two wire system with differential signal levels. The symmetrical pin layout of the RJ11 sockets on the Unitronics PLCs allows an easy way of interconnecting the PLCs with both RS232 and RS485 communications.

The diagram below shows a basic RS485 cable for use with the RJ11 socket on Unitronics PLCs. But You stated you are going to install this at a commercial setting, so it always better to use the worst case environment situations, and use shielded cable. These signals are commonly called A and B in RS485 systems. The A signals of all devices should be connected with each other and the same goes for the B signals. Now there was certain instances I used STP wire for rs485 because I had a lot of devices connected in a long run chain (DMX512 lighting fixtures). And the results before was a degraded signal that the devices near the end would interpret the signal incorrectly. 5 should work in your situation because of the voltage you will be running (5-10V) and your signal is not high frequency (above 500Mhz) in the first place. Two wire telephone cables will not function because in that case the ground signal levels on both sides will be floating.