36V5A true color LCD voltage and current meter made by sHMIctrl

The 36V5A voltage and current meter produced by sHMIctrl can measure voltage and current curves, has a true color LCD display, and contains a full set of source code. It can be used directly after purchasing components, soldering, and programming.

circuit design

1. Sampling circuit design

This is a very simple, practical and standard voltage and current sampling circuit. The basic principle is:

• The voltage is divided by R4 and R5 and enters the voltage AD sampling of the microcontroller; the voltage division ratio is 10:1, which means that for a full-scale AD of 3.3V, the actual measurable voltage is: 3.3*(10+1)=36.3V ;
• The current passes through the R11 sampling resistor. If the main GND is 0V, the voltage at the other end of the sampling resistor is related to the current. According to Ohm's law, V sampling voltage = I*0.025 ohms;
• The sampling voltage passes through an amplification circuit composed of operational amplifiers. The amplification factor is determined by R8 and R10. Vout=V sampling voltage*(27K+1.1K)/1.1K;
• Therefore, the voltage and current AD are connected to the two AD terminals of the microcontroller through the above circuit;

2. Assist in the selection and circuit design of microcontrollers

Considering accuracy and cost, we chose the cheapest STM32 microcontroller: STM32F030F4P6. This microcontroller has 20P pins, costs just over 2 yuan, and has 12-bit AD performance. The AD performance of STM32 is pretty good in the industry, so we chose This microcontroller

This is basically the simplest circuit of the microcontroller. In order to reduce costs, we do not use a crystal oscillator. It is worth noting that a mass production port for the flash program needs to be left for the microcontroller, otherwise the firmware of the microcontroller cannot be flashed; for this microcontroller, we choose The serial port is flashed, and communication also needs to use this serial port. For this reason, we need to set 2 short-circuit jumpers in the communication connection with the sHMIctrl controller to isolate the controller when flashing the program;

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