Formula Student Korea Electric Energy Meter

 

0. Features

• 100 Hz data recording
  • HV bus voltage
  • HV bus current
  • LV supply voltage
  • Ambient (CPU) temperature
  • Real-world time of each record
• USB Mass Storage data extraction
• Web-based data viewer

1. Specifications

	MIN	TYP	MAX	UNIT
Supply voltage1	6		28	V
Power consumption		0.25	0.5	W
HV bus voltage	0		600	V
HV bus voltage resolution		0.24		V/LSB
HV bus current	-750		750	A
HV bus current resolution		0.32		A/LSB
Operational temperature	-10		80	°C
IP rating		IP 20
Startup time		550		ms
Record interval		10	15	ms
Possible data loss on power brownout	0		100	ms

¹ When powered by USB, the device can startup with a minimum supply voltage of 4.5 V.

2. Connectors

Note

The HV current measurement terminals at the top of the device are standard-pitch M6 brass bolts.

	LV	HV
Model	Molex 5569-04A1 (39291048)	Molex 5569-02A1 (39291028)
Image
Mate	Molex 5557-04R (39012040)	Molex 5557-02R (39012020)
Pinout	1: D+   2: D- 3: VIN   4: GND	1: HV+   2: HV-

Tip

The crimp terminal for the Molex 5557 Series is Molex 5556T (39000038).

Wiring

The data cable and the drive cable are two distinct cables. When driving the vehicle, connect the drive cable to the LV connector of the device. To extract data, disconnect the drive cable and connect the data cable instead.

Caution

Misconnection of the pins may cause permanent damage to the device.

Tip

The easiest way to make a data cable is to cut a USB cable with Type-A connector on one end.

3. Usage

3-1. Record data

When driving the vehicle, connect both HV cable and drive cable to the device. The drive cable should supply VIN >= 6V to start recording.

Once the device is powered up, it performs a zero calibration of the HV voltage and current. After calibration, it continuously measures data every 10 ms.

The measured data is updated to the file every 100 ms. During the file update, next measurement may be delayed by up to 5 ms.

A new log file is created with each power cycle. Each log file corresponds to a single power session.

Important

For the precise calibration, make sure that the HV voltage and current are at 0V and 0A until the startup is complete (typically 550 ms).

Note

The device has an internal clock that tracks real-world time. Since the clock drifts over time, synchronize it with the FSK-EEM Viewer after a long period of non-use. If the time keeps resetting to May 12, 2099, the battery should be replaced.

3-2. Extract data

To extract the recorded data from the device, disconnect drive cable and connect data cable instead. There is no need to disconnect the HV cable during data extraction.

Plug the USB side of the data cable to the PC or smartphone (with a Type-A to C adapter). The FSK-EEM USB Mass Storage will appear shortly.

The log files are stored in the drive like a common USB memory. Copy the files to your PC.

Note

The drive is read-only; you cannot edit or delete the stored logs with the file explorer.

3-3. View data

Go to the online viewer and open the log file to view a graph of the recorded data, or export it in a human-readable JSON/CSV format.

Tip

If there is no Internet connection, download html or executable from the release in advance.

3-4. Configure the device

In the viewer's Device Configuration section, click Connect and select the device to connect.

The device's UID and the current time will be displayed on successful connection.

• Sync RTC: Synchronizes the device clock with the host computer.
• Delete: Erases ALL files stored in the device.

Unplug and reconnect the device to see the change after deletion.

Warning

The delete action cannot be undone.

4. DIY

4.1 Build hardware

1. Download fsk-energymeter-pcb.zip from the latest release and extract it.
2. Place a JLCPCB PCBA (SMT) order using the GERBER, BOM and CPL files at the gerbers/ directory.
3. Solder following parts manually to the device after the PCB arrives.
   • L01Z600S05 Hall sensor
   • 5557-02A1 HV connector
   • 5569-04A1 LV connector
   • 2.54mm 2*4 debug pin header
4. Insert the CR1220 battery and Micro SD card into the PCB.

4.2 Upload firmware

1. Download fsk-energymeter-firmware.zip from the latest release and extract it.
2. Connect 3V3, GND, SWCLK, SWDIO pins of the ST-Link to the corresponding pins on the device's debug pin header.
3. Run flash.bat to flash the release firmware to the device.

4.3 3d-print housing

1. Download fsk-energymeter-3d.zip from the latest release and extract it.
2. 3d-print both top.stl and bottom.stl files.

4.4 Final assembly

1. Prepare 1x busbar, 2x M6 nuts, and 2x M6*35mm brass bolts.
   • The busbar and nuts are custom-sized and must be CNC-machined.
     • The recommended material is C11000 copper alloy.
   • The 3D model of the busbar is at fsk-energymeter-3d.zip.
     • Dimensions: 75mm(L) * 12mm(W) * 6mm(H).
     • Distance between holes: 57.5mm (center-to-center).
   • The nuts are standard-pitch M6 hexagonal nuts.
     • Dimensions: 14mm(W) * 16mm(H).
2. Prepare 5x M3*4mm and 4x M3*20mm bolts for PCB and housing assembly.
3. Insert the busbar through the Hall sensor and secure it with the M6 bolts and nuts.
4. Place the PCB-busbar assembly into the housing and assemble the housing and cover.

Important

The HV current path is through the M6 nuts and the busbar. The M6 bolts are not intended to carry HV current. Therefore, the nuts must be thick enough to handle the current and provide sufficient contact area, and tall enough to be exposed above the housing cover.

5. Development

Note

This section is NOT REQUIRED in general, and is for developers who want to modify the software on their own.

click to expand

5-1. Firmware

Prerequisites

1. Clone repository

   git clone https://github.com/luftaquila/fsk-energymeter.git --recursive

2. Make sure the arm-none-eabi-gcc, openocd and make executables are in the $PATH.

   • Common
     • Arm GNU Toolchain (AArch32 bare-metal target (arm-none-eabi))
   • Windows
     • OpenOCD for Windows
     • Make for Windows
   • macOS

     brew install make openocd

   • Linux

     sudo apt-get install build-essential openocd

Build and upload

cd fsk-energymeter/device/firmware
make program  # release build
make debug    # debug build

5-2. Viewer

Prerequisites

1. Node.js >= v20
2. Clone the repository and install dependencies

   git clone https://github.com/luftaquila/fsk-energymeter.git --recursive
   cd fsk-energymeter/viewer
   npm install

Build and run

cd fsk-energymeter/viewer
npm run dev          # development server at http://localhost:9400
npm run build        # production build for Docker image 
npm run build:dev    # production build with no base url
npm run build:single # single file html build

6. Troubleshootings

1. FSK-EEM USB Mass Storage takes too long to be mounted

The device only supports USB Full Speed (USB 1.1) spec. It is decades-old technology with a maximum transfer speed of 12 Mbps. However, in the real world, the actual speed is around 4 Mbps (0.5 MB/s).

When the device is connected to the host PC, the host will try to load the FAT table of the SDMMC. The FAT32 FAT table is typically a few megabytes, so it will take ~20 seconds to mount.

To reduce the mount time, format SD cards with larger cluster sizes. The RTC sync or record delete functions will work immediately regardless of this limit.

2. Web Serial API not supported error on the FSK-EEM Viewer.

The FSK-EEM Viewer's Device Configuration tab uses the Web Serial API to talk with the device, which has limited support across the platforms and browsers.

7. DISCLAIMER

Important

차량기술규정 및 출력제한 위반 여부는 대회장에서 제공하는 공식 에너지미터로만 판단합니다. 그 밖의 에너지미터는 제조 공정의 차이 등으로 인해 공식 장치와 측정값이 상이할 수 있음을 반드시 인지해야 합니다. 이러한 에너지미터는 대회 중에는 사용할 수 없으며, 차량 제작 시 단순 참고용으로만 활용해야 합니다.

8. LICENSE

For non-commercial use only:

"THE BEERWARE LICENSE" (Revision 42):
LUFT-AQUILA wrote this project. As long as you retain this notice,
you can do whatever you want with this stuff. If we meet someday,
and you think this stuff is worth it, you can buy me a beer in return.

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