Analog and five-digit source meter/ammeter (1) control part

Introduction: A dual-display source meter that combines analog-digital fast response and digital reading, and can also be used as an ammeter.

This is a multi-purpose indicator meter that can be used as a USB source meter, or an ordinary ammeter. It has a large measuring range, fast switching speed, and is equipped with an LED analog indicator bar.


1. Product introduction:

A source meter that automatically switches the current display from 1uA - 1mA - 200mA - 1A - 5A to four ranges;

the range switching speed is fast and can be used for current monitoring when switching between low power consumption, sleep wake-up, etc.;

active amplification , low internal resistance, the maximum partial voltage of the current sensing resistor in all ranges is <=20mV (excluding the internal resistance of the mos tube);

by connecting USB2.0, you can directly connect the computer and the development board, and detect the development board current in real time.


2. Application scenarios:

electronic product development;

low power consumption testing;

low voltage electrical appliance repair.


3. Product Overview: An

operational amplifier is used inside the ammeter to amplify the sampling voltage to reduce the internal resistance. Four ranges are set in the schematic diagram, and other range allocations can be achieved by changing the sampling resistor.

Range switching is controlled by STM8. After the sampling voltage exceeds this range, the rising edge of the comparator output is used to generate an interrupt for STM8 to switch to a higher range.

TYPEC on both sides, the left side is input and the right side is output. The two CC lines and D+ D- data lines of the female socket are directly connected and can be used for protocol boosting or jumper connection to USB2.0 devices.

The circuit of this machine is powered by a battery (common ground), and the power input ripple does not affect the accuracy.

It can be used for conventional ammeters by HACKing the TYPEC male connector.

This project is a prototype, and it is known that there are still some shortcomings. Please be sure to read the attached: Special Notes_Please read the .pdf in advance.


4. Product parameters:

Power supply: Type-C

range and internal resistance (typical):

0-1mA: 20.05R (mos internal resistance 50mR);

1-200mA: 0.15R (mos internal resistance 50mR);

200mA-1A: 0.07 R (mos internal resistance 50mR);

1-5A: 0.014R (mos internal resistance 10mR);

long-term maximum current: 5A;

reverse voltage at VCC GND after shutdown: less than 20V;

accuracy: full scale up to 0.5 after calibration %, but the long-term stability has not been tested;

battery capacity: 500mAh, which provides about 5 hours of use. The charging method is to charge after shutting down, and the charging chip will be disconnected after turning on.


5. Instructions for use:

Schematic diagram of module connection method:

Use 12P soft flexible cable to connect the cable. For purchase link, please refer to the attachment: Purchase link.zip

The project is divided into: PCB, 3D printed shell, acrylic panel, battery, screen, and assembly accessories several parts.

PCB can be directly prototyped (2 pieces);

the source files for 3D printing and acrylic panels can be ordered at Lichuang Mall.


6. Note:

This project consists of two parts and requires cooperation: "Analog and five-digit source meter/ammeter (1) control part", please click on my homepage to view it.

Because some components need to be purchased additionally outside Lichuang Mall, the components and direct plug-ins that require additional purchase in the BOM list are set not to be mounted by SMT. Please mount these components manually.

In addition, if there is a small amount of PCBA, due to the large number of device types and high material replacement costs, you can also choose to only prototype the PCB and perform all manual mounting.


1. Due to the need for packaging, the op amp model in the schematic diagram does not match the actual model. The actual op amp model should be: MAX4239AUT+T (silk screen ABAA). Please pay attention to the corresponding instructions in the schematic diagram.


2. Before implementing this project, please be sure to read the attachment: Production Instructions_Please Read First.pdf.


3. This project requires a burning program. For the specific source code, please refer to the attachment: STVD source code.zip.

The source code needs to be opened by STVD. When burning, it needs to provide 3-5V power supply to the motherboard and share the ground with STLINK.


4. Cost composition:

Board 1 approx.: RMB 70

Board 2 approx.: RMB 45

3D printing shell: RMB 11

Transparent acrylic Finished acrylic 2.8 200*300 x1p

Transparent acrylic Finished acrylic 2.0 200*300 x1p

Due to the small size of the panel, the above will be Multiple sets of finished products, not included in the cost for the time being

Battery: ￥10

---------------------------------------- ------

The total cost of the complete set is approximately: ￥150 yuan (excluding PCB and SMT).

For the screen and battery, please refer to the attachment: purchase link.zip


5. It is recommended that the LEDs of board 2 be mounted using SMT, and the rest are mounted manually. .


6. Due to space constraints, the component number screen printing is not placed on the PCB. Please refer to the attachment:

Mounting point bitmap.zip.

You can print it out to facilitate mounting, or you can directly import the attachment:

Lichuang EDA professional version file. zip, use Easy EDA’s “Welding Assistant” to complete placement.


7. Attachment list:

Special precautions_Please be sure to read in advance.zip

3D printing (STL format).zip

Panel printing.zip

STVD source code.zip

Purchase link.zip

Structural dimension drawings.zip

Mounting point map.zip

Lichuang EDA Professional Version file.zip

Jialichuang EDA professional version file_v2.97_control.zip


7. Test video:

The video shows the accuracy test (after calibration) and the test of switching from microamp-5A gear.


8. Latest update:

2022-08-15 HW_2_2.97

In the previous version, the GND connection point between the main circuit and the sampling part was incorrect and has been updated.

This piece is still in the process of proofing, and there are currently no associated orders. Please download the file in the attachment for now: Jialichuang EDA professional version file_v2.97_control.zip, import it into Jialichuang EDA professional version and create a board (1.2mm).