Add a Bluetooth remote control setting circuit to the 4-20mA two-wire passive digital display meter

The RSL10 module is plugged into the self-made optocoupler isolation circuit board, and the entire module is connected in series with the modified target instrument (4-20mA two-wire passive digital display meter) and then connected to the 4- In the 20mA current loop, when the actual working zero current is 4mA, the target instrument displays 4.000mA in the current mode; the overall voltage drop of the circuit board of the work is 2.513V; the changed range or unit is sent to the RSL10 on the circuit of the work through the mobile APP Setting command, the target instrument (currently its own voltage drops by more than 1V) will be changed by Bluetooth remote control to change the setting state, such as switching to different ranges or displaying different measured physical quantity units, etc.

In actual industrial field applications, various 4-20mA two-wire sensor transmitters normalize the measured physical quantity into a 4-20mA current, and then send the corresponding voltage signal to the industrial computer through the sampling resistor. Or PLC, etc. for subsequent control processing; in order to facilitate human-computer interaction, a large number of digital display instruments that can display the measured loop current or the physical value corresponding to the current on-site in real time have appeared on the market - which is the target instrument to be transformed in this project: 4-20mA two-wire passive digital display meter. Most of these meters can make some settings changes through their own button operations. The meter I want to modify needs to be connected to the computer and then made through special PC software. It only requires changing the settings. With the help of this RSL10 application competition, I want to transform it into a function that can be used to change settings online on the spot through the mobile phone Bluetooth APP.

The final choice of the project shows that no matter whether the modified circuit is front or rear, there is no need to worry about the fluctuating ground voltage difference between the target instrument and the target instrument. This is the process of choosing a method of communication by optocoupler to avoid current short circuit; Passionate about adhering to the simple and effective principle of "do not add more entities if necessary", after deciding to use optocoupler communication, some circuit power supplies were modified without boosting or bucking, and only used positive voltage generated by simple silicon diodes connected in series. The voltage drop is used as the working power supply, and even the LDO is omitted. As long as the RSL10 can drive the optocoupler under limited current, such a plan is so simple that it seems that there is no design, and the peripherals are "cheap". It can also achieve "higher" circuit functions, obviously relying on the excellent performance of RSL10 integration.