Help! Bike sensors tracker electric circuit review - Page 1
Forum section: electronics / beginners

author: jim87
author_rank: Newbie
timestamp: October 02, 2025, 07:59:27 am
content: Dear EEVblog community.It's my first attempt in designing a custom hardware component which gets data from various sources (OBD II port and other sensor chips) with no prior electrical engineering knowledge.So I started sketching something, based on (1) LLMs, (2) data sheets and (3) trying hard to understand what was going on. It went complex in nanoseconds, and thus I started modularizing the project using sub-sheets.Now I have my first electrical schema quite done, at least in its first draft.Link to the project (which is open source! yay!):GitHub - elegos/bike-sensors-loggerThe project is all about connecting the device to the OBD II port of a vehicle (my interest is in bikes), take some data from the CAN bus directly and others from dedicated chips (accelerometer, gyroscope, GNSS) writing all the info down in a microSD. A bluetooth module (which I have not integrated yet, as I’m still studying which chip and which connections) will be added to the solution, to become an external GNSS module for devices like action cams (and thus syncronize the videos with the data), and possibly a future connector for real-time data sharing (smartphone app? Satellite device? Who knows). A magnometer might be added to the accelerometer / gyroscope chip, as it supports sub-sensors, but that’s not a priority right now.An external battery (I was thinking about a CR 2032) should be added to power the GNSS chip during stand-by, though I haven’t added it yet.I’ve split the project in several sheets:Main sheet: the project as a whole. The core processing unit is an Arduino Nano R4 board (yes I wish I had the time / experience to “transfer” the arduino scheme into the project’s to avoid PCB-on-PCB embedding, but not today)OBD II port: from which I get 12V power and the CAN bus for RPM and speedSome status indicator LEDs(1 for power, 1 for GNSS antenna type (active / passive) –> see later)Subsheet: 12V to 5V and 3.3V bucks (step down buck converters): to get 5V and 3.3V down from 12V and power all the chips (5V for Arduino, 3.3V for the rest of the components).Subsheet: Accel-Gyro: the accelerometer + gyroscope chip and relative circuit.Subsheet: GNSS: chip to get clock and position data. It has a sliding switch which should (in theory) activate the power for the antenna, and at the same time enable the status LED. This allows the user to either use a passive antenna (switch off) or a 3.3V active antenna (switch on), depending on his/her needs.Subsheet: OBD II Transreceiver (subsheet): details how I manage the CAN bus and the bus’ termination (which AFAIK can or can not be done earlier in the vehicle’s circuits)Subsheet: MicroSD: the micro SD connector, with some resistorsThe sub-sheet circuits have been designed following the example schemas found on the technical documentation of each chip, but I think I need to review at least the bucks, as I don't understand for example the existance of R1 before the feedback loop (which might be a technical doc schema error perhaps? It is not explained by the docs apparently).Before proceeding with the PCB design (and receive hints on how to design it, too), I’d like to have a review of the electrical schema by someone who knows about electric engineering: for this task though unfortunately I have no friends, collegues or contact in this field, and thus I’m here to ask help.Thank you for your kindness!GiacomoEDIT: attached both the schematics and the BOM (csv format).

author: thm_w
author_rank: Super Contributor
timestamp: October 02, 2025, 10:04:39 pm
content: Fixed link:https://github.com/elegos/bike-sensors-loggerPlease consider using PDF for schematics, otherwise people have to download kicad (of a specific version) just to view your design.

author: jim87
author_rank: Newbie
timestamp: October 03, 2025, 07:23:15 am
content: Thank you thm_w for the hints,I've corrected the link and uploaded the latest pdf (schematics) + csv (BOM).In the meanwhile I did a review by myself of the 5V buck, I think I'll have to do similar changes to the 3.3V one.I'll keep the schematic and the BOM updated as I proceed.Thanks for your support!

author: thm_w
author_rank: Super Contributor
timestamp: October 03, 2025, 10:23:38 pm
content: Schematic looks good.In terms of style usually we put the capacitors below Vcc going to Gnd.Quote from: jim87 on October 02, 2025, 07:59:27 amIts not an error, but in the datasheet R3/C8 in your schematic are greyed out as being optional. You can leave as is and just not populate those components. You can read more:https://electronics.stackexchange.com/questions/634289/what-is-the-function-of-the-feedforward-capacitor-on-the-lm2596-adj- There is an error on U3 where you've tied FB to Vin- CS from U2 should be connected to your MCU, you may also consider connecting INT1 even if you aren't using it yet.- I dont see any pullups on SDA or SCL, I dont know if these are built into the nano R4 or not.- Sometimes you want pullup/down on the microSD as well.

author: jim87
author_rank: Newbie
timestamp: «Reply #4 on:Todayat 07:29:43 am »
content: Hello thm_w,thanks for the review- R1 in the previous revision was between the current C7 and 5V output, I removed it before rev1. As far as I understand R1 + R2 are a voltage divider, while R3 + C8 are used to stabilize the output ripple, am I correct?- You are right, FB and Vin of U3 should not connect each other! Thanks for spotting it- U2's CS is a digital value that should be 1 to enable I2C connection, correct?- There should be internal Arduino Nano R4 pullups, but will check. May you please explain me better about this?- I'd want to pullup/down the microSD for SD preservation, or battery saving? In theory this device writes once per second, up to 10 times per second (I think it'd be better to have a little memory cache and write once per second to avoid continuous writing).Thank you very much

author: jim87
author_rank: Newbie
timestamp: «Reply #5 on:Todayat 01:41:11 pm »
content: Ok, I made the following changes:- Removed U3's FB and VI shortcircuit (typo)- Connected U2's CS pin to 3.3V in via a 4.7 k resistor (to always enable I2C communication)- Added a level shifter to manage I2C pins between arduino (5V) and the other components (3.3V)- Added 4.7 k pull-up resistors on the A side of the level shifter (3.3V) to pull-up I2C's SDA and SCL lines