Mystery MCU electronic park disk - Page 1
Forum section: electronics / general

author: bluespresso
author_rank: Newbie
timestamp: October 13, 2025, 06:13:09 pm
content: Can anyone help identify this mystery MCU? (3F 16 11 02)It controls an electronic park disk.48 pin package.2,8v VDD as provided by U2 (54FK). Connects to pin 6 and pin 10.GND pin 13.Connects to a crystal oscillator (T120A) on pin 4 and pin 5.VDD pin 46SCK pin 45SDA pin 44Pin 39 should have PWM capability because it should provide through a 10k resistor a signal to Q1 to drive the buzzer.A lot of the pins are used to drive an LCD display on the back side.I suspect that U3 is an accelerometer (XV1 22).The PCB ist titled “AOK – 2137 Main PCB V1.0”The circuit draws around 18µA @ 3V when not in motion. Display is on and the battery symbol can be blinking. The blinking does not change the current draw.When motion is detected approx. 180µA are drawn constantly until rest.Here is my issue with the design:When the 3V battery fades the battery symbol should always be blinking. Instead the symbol only blinks when motion is detected. Under the 180µA the voltage slightly drops but then recovers when in rest so the battery symbol does not blink any more. In the normal use case you can never see the display when you are driving. This leads to a situation where you have never seen the battery symbol blinking but the voltage drops so low that the MCU resets. The programming should rather be that if after initial setup low voltage is detected once the battery symbol should never stop blinking (even if the battery recovers in idle state).Also this device should, if battery is low, beep every time it changes state from rest to motion so you know it is time to change the battery. Unfortunately, is does not do so. The buzzer is working. I tested it with a signal generator. I assume it is not programmed correctly.Also I am wondering if it is really necessary that it constantly draws 180µA when in motion. In my opinion the device could just detect the motion and then maybe sleep for 30 seconds consuming only 18µA then wake up and if motion is detected again immediately sleep for 30 seconds. Only if no motion is detected after wake up set the parking clock. I think this could drastically increase battery life.Ideally I would like to take control of the chip and create my own firmware. I tried to connect to it via Pickit 3 but nothing seems to work.Another possibility would be to replace the MCU but it may be difficult to find a pin compatible one that at the same time could match this chip in the low power draw.

author: PeterG
author_rank: Frequent Contributor
timestamp: October 13, 2025, 09:31:11 pm
content: My guess would be an STM32 MCU.The pinout your describing matches the STM32F103C8T6.Best of luck.

author: coromonadalix
author_rank: Super Contributor
timestamp: October 13, 2025, 09:47:43 pm
content: seems so if you can get your hands on any cheap stlink programmer or any who can or could identify it, stm32cube programmer (free) but need registration, once linked you know who it isBUT keep in mind even if it's really an stm32, the code may be locked in, no read possible thus you wont get far, unless they have not locked it (could be loll)you would need to fully reverse the pcb and catch all the signals / data with a logic analyzer and do your own code

author: abyrvalg
author_rank: Frequent Contributor
timestamp: October 14, 2025, 05:48:41 am
content: IMO there are no matches with F103C8 at all: oscillator pins are off by 1, VDD/GND are on ports, ISP is neither SWD not UART. I’d rather suspect some obscure Chinesium.

author: pcprogrammer
author_rank: Super Contributor
timestamp: October 14, 2025, 06:27:03 am
content: For sure not an STM32F103C8T6. Pin 44 is BOOT0 and not some programming interface pin.The programming pins are marked as if they are I2C based, but there are no pull up resistors visible. Could be integrated in the chip, so you can try if it responds to some I2C read addressing. Using open drain without pull ups should not harm anything. If it responds to some address a small piece of the puzzle is recovered, but would still leave a big question mark as to which MCU it is.The ISP connector also having a pin marked VPP brings the question what voltage it would need for programming.abyrvalg is most likely correct in that it is some obscure Chinese MCU for which no documentation will be freely available, let alone a compiler.

author: TinLethax
author_rank: Regular Contributor
timestamp: October 15, 2025, 07:21:18 am
content: Could it be from NXP?Also Chinese MCU manufacturers just to name a few...-Nuvoton-HOLTEK-PUYA-Padauk-STC Micro-Titan Micro

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: October 15, 2025, 08:21:23 am
content: If it's not some obscure Chinese part, I'd start at Digikey, MCUs section, filter by package then ascending by price, and look through the datasheets.However as it's not marked, it's pretty likely that it is something obscure. Might find it on LCSC but their search can make it hard work.Having an on-chip LCD controller narrows it down somewhat.