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Description

Imported from GitHub: Tosainu/gnss-7-seg-clock · commit b5fd36e · license MIT

Description

GNSS-powered, seven-segment table clock

README

GNSS Seven-segment Clock

GNSS-powered, seven-segment table clock.

DSC_8405

https://github.com/user-attachments/assets/9b2d0560-d879-4ddb-b99d-07a6e9839360

Full video: https://www.youtube.com/watch?v=Y1P_iDvq4bk

Firmware

Usage

Pre-build firmware files are available on the release page. Thanks to the RP2040 Bootrom, flashing the firmware requires no special tool. Connect the board to the PC using the USB-C cable, while holding the BOOT button (SW2). Once the RPI-RP2 drive appears on the PC, copy gnss-7-seg-clock.uf2 there. The board will automatically be rebooted as soon as it finishes writing to Flash.

  • The board displays --.--.-- until it obtains the time information.
  • Press SW3 to change the display contents:
    1. Time: hh.mm.ss
    2. Date: YY.MM.DD
    3. Configuring time zone (time offset): [-]hh.mm
      • SW4: + 30 min
      • SW5: - 30 min

Build

The firmware is written in the Rust programming language with the Embassy framework. In order to build the firmware, you first need to prepare the Rust toolchain. Please refer to the official guide.

Next, install the linker helper flip-link. Alternatively, remove this line to use the default linker.

$ cargo install --locked flip-link

Lastly, run the command below to build the firmware. You can find the ELF file ./target/thumbv6m-none-eabi/release/gnss-7-seg-clock afterward.

$ cargo build --release

If the debug probe is attached to the board and probe-rs is installed on your PC, cargo run can be used to load firmware to the board.

$ cargo run --release

# to run test apps in crates/gnss-7-seg-clock/examples/
$ cargo run --release --example gnss-uart-pipe

Schematic and PCB

[!IMPORTANT] I'm new to circuits and PCB designs. Any feedback and advice are welcome! (✿ゝ◡╹)ノ

I designed the Rev.A board with KiCad v8.0.8 (Linux/macOS) and their official libraries. You can find the KiCad project files in the hardware/ directory. You can also find the rendered schematic (PDF) and Gerber files on the release page.

DSC_7465

DSC_7464 Please do not take a close look at 43-44 pins of RP2040! (ignorable solder bridge)

Parts

[!NOTE] Tolerances were set by just referring to several existing designs. Some of them might be insufficient or overkill.

ReferenceValuePartsQty
C1, C2, C4-C10, C14, C17-C19MLCC, 0.1uF, 10%, 6.3V, X5R, M100513
C3, C11MLCC, 1uF, 20%, 6.3V, X5R, M10052
C12, C13MLCC, 10uF, 10%, 6.3V, X7R, M20122
C15, C16MLCC, 15pF, 5%, 50V, C0G/NP0, M10052
C20MLCC, 10000pF, 10%, 16V, X7R, M10051
C21MLCC, 47pF, 5%, 50V, C0G/NP0, M10051
D1Bidirectional TVS, M1005Littelfuse PESD0402-1401
D2-D7LED, M10056
J1USB-C ReceptacleGCT USB4105-GF-A1
J2SMA Receptacle, Edge MountMolex 7325111531
J3Pin header, 01x03, P2.54 mm1
L1Inductor, 27nH, 5%, M1005Murata LQG15HS27NJ02D1
R1-R3Resistor, 2.2kOhm, 1%, 1/16W, M10053
R4, R5, R12, R14-R16Resistor, 10kOhm, 1%, 1/16W, M10056
R6, R7Resistor, 5.1kOhm, 1%, 1/16W, M10052
R8, R9Resistor, 27Ohm, 1%, 1/16W, M10052
R10, R13Resistor, 1kOhm, 1%, 1/16W, M10052
R11Resistor, 10Ohm, 5%, 1/4W, M10051
R17-R22Resistor, 470Ohm, 1%, 1/16W, M10056
SW1-SW5Tactile SwitchC&K PTS8105
U1-U67-segment LED, Common-Anode, 3.81 mm6
U7-U916-ch LED sink driver, SOIC-24WTI TLC5925IDWR3
U10MCURaspberry Pi RP20401
U11LDO, 3.3V, 500 mA, SOT-23-5TI TLV75533PDBVR1
U12SQPI NOR Flash, 32M-bit, SOIC-8Winbond W25Q32JVSS1
U13GNSS Receiveru-blox MAX-M10S1
Y1Crystal, 12MHzAbracon ABM8-272-T31
GNSS Active Antennau-blox ANN-MB51

Seven-segment LEDs

U1-U6 are seven-segment LEDs, the essential components in this design. While selecting them, I was surprised about the poor availability of seven-segment LEDs, especially the larger models (> 1″). I wanted to use Kingbright SA15-11GWA initially. However, due to the availability and price, I selected WENRUN LSD150BAG-101, even though I had to use a different store from other parts.

Unfortunately, LSD150BAG-101 is not a drop-in replacement for SA15-11GWA. They have a different pitch for the vertical direction: 40.64mm (SA15-11GWA) and 40.00mm (LSD150BAG-101). Since I wanted to have some flexibility in the design, I made the footprint that uses the oval pad so that can use both types of seven-segment LEDs.

The forward voltage also has to be taken into account for U1-U6. Vf should be smaller than the USB VBUS. For instance, high-luminance types are not suitable in general.

Driving Seven-segment LEDs with Fewer Pins

U7, U8, and U9 are 16-ch shift registers specialized for the LED, TI TLC5925IDWR. Thanks to this three-cascading configuration, it can drive six seven-segment LEDs (48x LED segments) only by five pins.

TLC5925 determines the output currents based on an external resistor between the R-EXT pin and GND. R1, R2, and R3 are the current-set resistors for U7, U8, and U9 respectively. With the 2.2kOhm resistor, the output would be (1.21 / 2,200) * 18 = 9.9mA.

LDO and Capacitors

U11 is the 3.3V LDO, TI TLV75533PDBVR (TLV755P-series). I'm hoping it works nicely with an AC adapter/wall charger as well as a PC because of its good PSRR in wide-range frequencies.

C12 and C13 are the input and output capacitors for the LDO. According to the datasheet, TLV755P requires a 1uF+ input capacitor and a 0.47uF+ output capacitor while considering the DC bias characteristics of a capacitor. Based on this, I selected 10uF/6.3V MLCC.

RF Circuitry for MAX-M10S

sparkfun/SparkFun_u-blox_MAX-M10S is very good material as well as the MAX-M10S Integration manual. For the RF part, I imitated SparkFun's board and filled in parts values based on the reference design mentioned in the integration manual. Here are the parts correspondences between this board and the MAX-M10S reference design:

This boardReference designUse
C20C14RF Bias-T Capacitor
C21C18DC Block Capacitor1
L1L3RF Bias-T Inductor
R11R8Antenna supervisor current limiter/shunt resistor

D1 is the ESD-protection TVS which is only in the SparkFun's board. Since I have no confidence in finding compatible parts, I used the same TVS Littelfuse PESD0402-140 in this design.

Special Thanks - PCBWay

I would like to say a special thank you to PCBWay for reaching out and sponsoring my project. As part of the sponsorship, I had the opportunity to try their PCBA service. Overall I am very satisfied with the service and quality of the PCBs. Especially,

250316-133125-DSC_8347

Note that I made some changes from the Rev.A design for this order, such as changing footprints to a non-HandSolder variant. If you're interested in about the design files I used to order, please refer to the Rev.A2 release.

License

The project is licensed under the MIT license unless otherwise stated.

PCD design files, specifically the files under the hardware/ directory are licensed under the CC BY-SA 4.0 license. Please note that:

This project is inspired by Kello version 4.

Footnotes

  1. Apparently, this capacitor can be removed as my design doesn't have an external SAW filter. The built-in DC-block capacitor of the module is sufficient. ↩

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