If possible, I would also like if the current limit could be seen and set beforehand, with a slightly more advanced way than 'just short the leads.' Maybe a button that shorts the output for you, high tech! Those Constant Voltage and Constant Current LEDs could also be nice, but not really required.

For displays, we have some basic voltage ones at school, but for current, I've been thinking about this amazing thing: So very precise current control would be pretty neat. I like the simplicity of potentiometers, so analogue Coarse&Fine adjustment pots are good. The requirements would be 0V to 20V, around 3A and variable current control. I have found these two schematics while researching this, but don't know if they are any good, or even if they provide what I need. The problem is that I don't have any experience designing circuits. Don't really have money to buy one, but I happen to have availability to a ton of free components and a PCB mill courtesy of my school. Then it sends the request byte sequence for the respective nutrient.I'm in a need of a variable PSU, after getting frustrated with an ATX PSU and a 3$ regulator thingamajig from china. In each function, it first sets the DE and RE pins high, indicating that it wants to write to the bus.

These are the functions that handle sending the request byte sequences to the sensor and reading the response. Compile the code & upload it to the Arduino Nano Board. Download the following OLED Library and add it to the Arduino IDE. Since we are using OLED Display to display the Soil Nutrient values ( Nitrogen, Phosphorous & Potassium) in mg/kg, you will need OLED Library. The HEX code needs to be converted into Decimal to get the Measured Soil Nutrient content data. You can send the command and retrieve the value in HEX Code. The source code for interfacing Soil NPK Sensor with Arduino & retrieving Soil Nutrient value from the Sensor via Modbus command is given below. For example, if you get 0030 as a response then Soil Potassium Value will be:Ġ030 H(hexadecimal) =48 (Decimal) => Potassium = 48mg/kg You can calculate the Soil Potassium from the Response you receive. You will get the following as a response: The inquiry frame for getting Soil Potassium Value is: Interfacing Soil NPK Sensor with Arduino.

Fritzing variable power supply