Four-digit display header design

Last year, I helped others customize a four-digit display head, which can be used to measure various sensors with 4-20mA or 0-5V, 0-10V output.Set the display range, upper and lower limit alarm lights.Due to later changes to the plan, this plan is temporarily put on hold.Today, let's share the design process of software and hardware.

1. Hardware Design

1.1 Power

The power supply adopts a TL431+a triode to form a linear voltage regulator circuit.In this way, on the one hand, the cost is low, and on the other hand, the input range of the power supply can be enlarged (the input range of ordinary chips such as 1117-3.3 is only 16V).In addition, TL431 can also provide reference voltage for ADC.

1.2 Display Design

The single-chip microcomputer can be used to drive the digital tube directly, but it will occupy more IO ports, and the software design is slightly complicated. Here, a TM1650 is used to drive a 4-bit common cathode digital tube.

1.3 MCU and AD sampling

The microcontroller uses STM32G030F6, the built-in ADC supports hardware oversampling, and can achieve 16-bit resolution.Collect current or voltage by selecting an appropriate resistor.When collecting 4-20mA current, R12 is 0R and R4 is 150R.When sampling the voltage, R12 and R4 select the appropriate resistor divider to make the input range within 3.3V.If it is to directly collect the power supply voltage, short-circuit R13.

Another ADC channel collects the VREF pin of TL431 as a reference voltage.

1.4 Alarm Design

Two optocoupler isolation alarms (super-high alarm, ultra-low alarm) outputs, and external triodes are added to drive relays and other devices with larger currents.In addition, there is a buzzer (passive) on the board, and the buzzer interface is also led out, and the buzzer can also be externally connected.

1.5 keys

Two buttons are used to set display parameters, alarm parameters, calibration, etc.The two buttons can be led out to the terminal at the same time, and external buttons can also be connected.At the same time, the two buttons use the pins of the serial port function, and the program can be modified to realize the serial port output and setting.

The final PCB board is as follows, with the digital tube on the back.

2. Software design

In software, it is designed with STM32CubeMx and drives TM1650 with hardware I2C1 interface.Two ADC channels are used to collect the input current and the reference voltage of the TL431.Use TIM3CH1 to output PWM wave to drive the buzzer.The others are 2 alarm IOs and 2 key IOs.As follows:

The software implements the following functions:

Things are only made one version, the software and hardware design may not be perfect, for reference only.

There are more than a dozen left on hand, if anyone needs it, they can take pictures directly on Taobao (25 yuan for free shipping, schematic diagram and source code):

https://item.taobao.com/item.htm?spm=a1z10.1-c.w4004-8192824768.10.26ba1b9dUXLv4R&id=668157221254

If you only need the source code and schematic diagram, take the link below (2 yuan).The development is not easy, I hope everyone will bear with and support.

https://item.taobao.com/item.htm?spm=a21dvs.23580594.0.0.621e3d0dr3HE70&ft=t&id=679567748409