Designs for an open source bike computer.
Similar projects:
- https://github.com/vincent290587/stravaV10
- http://opencyclingcomputer.eu/
- https://gitlab.com/PrzemoF/Open-Cycling-Computer
- https://github.com/hishizuka/pizero_bikecomputer
| Item | Dimensions | Cost | Using | ||
|---|---|---|---|---|---|
| Display | |||||
| $13 | Yes | ||||
| Battery and charging | |||||
| 3.7v Lithium Polymer 3200mAh | 50 x 75 x 7mm | $8.50 | Yes | ||
| Receiver pad | 0.5mm thick | $3 | Yes | ||
| Charging base | $4 | Yes | |||
| Storage | |||||
| 16gb micro SD card | $5 | Yes | |||
| Microcontroller and modules | |||||
| ESP32 with LiPo charging | $5 | Yes | |||
| nrf52840 | $5 | Yes | |||
| GPS module | $5 | Yes | |||
| SIM800L module | $4 | Yes | |||
| Micro SD card module | $1 | Yes | |||
| Case | |||||
| Glass screen protector | $2 | Yes | |||
| 3D printed enclosure | Yes | ||||
| Glue | Yes | ||||
| 4 mounting screws | Yes | ||||
| 4 threaded heat inserts | Yes | ||||
| Rubber o-ring cabling | Yes | ||||
| Total |
LS027B7DH01 The A indicates maximum of two bright pixels. Need an FPC 10 pin connector
3D printed
The buttons are capacitive pads. These pads will be a separate PCB that you can glue onto the 3D printed case. This will be a water proof seal. Will the capacitive pads be sensitive to rain?
Maximum target dimensions: 55 wide, 80 long, 20 high
Need the on off control and charging port to be water proof.
ESP32 has 10 capacitive-sensing GPIOs. So you don't need to include any extra components to use capacitive buttons The nrf52 series also don't require any external componenents.
The capacitive pads could perhaps also go under the screen protector. I'm guessing a screen protector wouldn't reduce the touch sensitivity that much. This would serve as protection for the capacitive pads.
It is important to reduce the parasitic capacitance and increase the touch capacitance. How to optimize: reduce trace length by optimizing PCB layout; reduce thickness of the overlay; enlarge electrode's area. Could have surface mount pins to reach PCB below.
https://www.embedded.com/making-capacitive-touch-sensors-water-tolerant/
https://www.youtube.com/watch?v=lQ157ftTnSs
Google maps platform has a $200 free monthly usage. Could use their route planning.
2.42" OLED Not the best choice since they compete with sunlight.
Reflective LCD
https://www.buydisplay.com/blog/what-are-the-main-differences-between-LCD-and-OLED.html
https://www.buydisplay.com/3-4-inch-graphic-touchscreen-lcd-cog-module-240x160-single-sided-fpc https://www.buydisplay.com/3-inch-touch-240x120-graphic-displays-lcd-serial-interface-black-on-white
https://forum.arduino.cc/index.php?topic=188040.0 https://forum.arduino.cc/index.php?topic=488097.0 https://forum.arduino.cc/index.php?topic=554754.0
Vincent's stravaV10 uses Memory LCD LS027B7DH01 https://makerdyne.com/2015/02/08/large-memory-lcd-breakout-board-details/ https://makerdyne.files.wordpress.com/2015/12/MemoryLCD_Breakout_Board_Schematic.pdf
The LS027B7DH01 with a backlight by Flex: https://www.digikey.com/products/en?mpart=11103-06_T5&v=2004
This both for convenience and keeping the enclosure waterproof. Quite cheap for a whole setup. The pad inside of the computer can be very slim.
This one is small enough to be away from antennas. https://www.mouser.co.uk/ProductDetail/PulseLarsen-Antennas/WMRR124F-2?qs=w%2Fv1CP2dgqrPY4DsgoYlEg%3D%3D
https://www.instructables.com/id/RFID-NFC-Tap-and-Go-Ring-for-Credit-Card-Payment/
Could just have a thin slot for a pay as you go card (Revolut or Monzo).Could have SMS notifications so that the bike computer knows when you have paid. Set up that sim with that bank card. Could acetone the bank card to make it slimmer.
https://lastminuteengineers.com/sim800l-gsm-module-arduino-tutorial/ I hope to be able to use the microphone pins to play pre-recorded messages.
Pin choice: It seems like the nrf52840 are pretty multi-purpose. For high-frequency stuff, try and avoid pins close to the antenna to avoid interference. https://devzone.nordicsemi.com/f/nordic-q-a/52857/recommended-pin-usage
P0.0 = 0, P0.1 = 1 .... P0.31 = 31 P1.0 = 32, P1.1 = 33.
Sharp memory schematics: https://makerdyne.files.wordpress.com/2015/12/MemoryLCD_Breakout_Board_Schematic.pdf
One set of SPI pins per peripheral: they might work at different speeds. And I think the asynchronous aspect would mean the LCD could be prioritized.
https://github.com/DF4IAH/HFT-Core-Module
Antenna: SIM868 is L1 band. Glonass L1: about 1602 MHz GPS L1: 1575.42 MHz Beidou: 1575.42 MHz (Possibly lower: 1561.098MHz?)
https://www.antenova.com/integration-hub/antenna-selection-tool/
Drawing antennas as part of the PCB seem like a bad idea. They take a lot of testing.
Mouser sells the SR4L049 (both left and right versions) for about 3 dollars. SR4L034 is very similar.
The M20057 and M20047 modules combine the SAW and antenna. Power consumption is about 2ma,
M20047 cost: 4.50 gbp from mouser and at digikey B3913 cost: 1.62gbp SR4L034 cost: 1.44 LNA?:
I'm pretty sure it needs an LNA. So I'm going with https://www.u-blox.com/sites/default/files/NEO-8Q-NEO-M8-FW3_HIM_%28UBX-15029985%29.pdf
Picking a saw filter from Mouser
SAW filter: You want something in the middle of the frequencies, so 1588ish and that has a wide enough bandwidth to capture the signals. Two come up: B3913 and B3413. The B4310 is used in the HFT-Core-Module. B4310 is from 2015. The B3913 and B3413 are very similar but the B3413 is newer and has improved electrostatic discharge (ESD) robustness. Qualcomm RF360 website SAW filters for GNSS. B4310 doesn't have Beidou next to it on the website. I can't find the B3413 in stock, so I'm using the B3913 in stock at digi key.
- The wireless charging setup.
- Battery level indicator.
- Why polarized capacitor in decoupling?
- RF SYNC
- What about low noise ammplifer LNA?
Two pcb design Have a pcb at the top. This has a cut out for the screen. This top pcb has capacitive buttons. On the underside of this top pcb, are an on off switch and maybe the usb port. Also could have pressure, temperature, humidity sensor as it should be on the outside? The traces are the link between the outside and the inside. The 3D printed bottom port of the case could just be unibody. There would be pcb to pcb connectors. The top pcb would have surface mounted pins on the underside. The bottom pcb would have the female connectors. When you align the pins, the top pcb drops into the bottom one. These are pin and socket There would be o-rings around each of the mounting screws and o-ring cord going around the perimeter.
The two PCBs could fit together inside the 100x100mm size.
Could this extend the ground plane?: https://blog.antenova.com/how-well-can-an-embedded-antenna-perform-on-a-tiny-pcb
Threaded PCB inserts could provide a flush mounting style.
Connections between plates:
- Ground
- VCC
- Battery switch
- Data+
- Data -
- 5x buttons
- Temperature, pressure, humidity sensor.
Connectors: https://www.samtec.com/products/ftsh
Pins:FTSH-104-01-F-DV Connector: CLP-104-02-F-D