RS485 4 in 1 Soil Probe
egmenard 2026-05-22 11:22:24 206 Views1 Replies I'm trying to rig up the soil probe to be used in remote field research for manual data collection (not continuous) where a laptop is not practical. Therefore, I am trying to use an Android phone with modbus app. I'm currently using a rs485 usb adapter and usb to usb-c adapter to the phone and a 5V usb power bank. I have yellow and blue wires to pins 1 and 2 respectively, brown to red power source and black probe + black power to pin 5. The app runs but it appears there's no power to the probe. The TX light on the rs485 adapter blinks when I ask for a read but the RX does nothing. All the app configurations should be correct. Any suggestions?
A power and RS485 bus check may be a good place to start.
It may help to measure the voltage between brown and black at the probe end while everything is connected. With the USB power bank, it should be close to 5V. It is also worth checking that the probe GND and the USB-RS485 adapter GND share a common ground.
Another easy thing to try is swapping yellow/blue on the RS485 adapter, since A/B labels are not always consistent. The default Modbus settings to compare against are RTU, slave ID 1, 9600, 8N1, function 03, start register 0x0000, length 4. The raw query frame is:
01 03 00 00 00 04 44 09
If TX blinks but RX still does not respond after those checks, it may help to test the same sensor and USB-RS485 adapter once on a PC. That would make it easier to separate phone OTG/app compatibility from wiring or RS485 bus issues.
Yx 
