Advice on hardware connection

[henkjan_nl]

Hi,

I am a mechanical engineer seeking mechanical advice .

I'm developing a handheld GPS which should meet my following requirements:
1. compact
2. robust
3. easy to assemble

The device contains the following components:
1. ESP32 board (MH-ET Live Mini)
2. 3.2" touch screen
3. Beitian BN-180 GPS
4. Accelerometer BMI-160
5. Micro SD card (currently not working)
6. A battery compartment for 3 AAA batteries
7. A power switch

I developed a 3D printed housing which really looks nice and works well.

CAD model

3D Model - 700.jpg (50.4 KiB) Viewed 3701 times

Together, this forms a really nice platform to exercise my programming skills (which I will need a lot).

Device working

Device working - 700.jpg (79.66 KiB) Viewed 3701 times

It works quite well, only soldering of the 37 wires is a really tedious and error-prone job (74 soldering connections!).

Device open

Device open - 700.jpg (189.64 KiB) Viewed 3701 times

I am contemplating learning how to use KiCad and develop a motherboard to hook everything together. Only, if I connect everything with pin headers, the device will bevome quite large. If I solder everything together it will sure be easier and faster than with wires, but it will be virtually impossible to take it apart.

Any advice on the right approach?
1. Is KiCad the right choice?
2. Solder everything together, or partly, or else?
3. Which types of connectors are best to use?

Help is very much appreciated. Kind regards,

HenkJan van der Pol.

[becorey]

I've heard kicad is good. I use easyeda, very easy to get started and has huge component library. I'm also a mechanical engineer taking on electrical work, it's not so bad.

If you layout your own board, you can move away from these modules and just put the components on your own board. Then you won't have as many connections as you're imagining now. The dev boards and breakout boards are good for prototyping and verifying the functionality but not for final product.

1. ESP32 board (MH-ET Live Mini) -- definitely put the esp32 on your own board. Probably a wroom or wrover module, being easiest to use.
2. 3.2" touch screen -- usually a screen has a flat flex cable and just needs something like a ZIF connector on your board
3. Beitian BN-180 GPS -- maybe keep this one as a module
4. Accelerometer BMI-160 -- easy to put accel / gyro / imu chip on your board
5. Micro SD card (currently not working) -- easy to put micro sd connector on your board
6. A battery compartment for 3 AAA batteries -- are you sure you want AAA batteries? You could do a thin li-ion or li-po battery with usb recharging. Smaller size and more energy density
7. A power switch -- easy to put on your board

[henkjan_nl]

Thanks for this reply too.

I'll both consider Kicad and Easyeda.

The idea of designing a full board based on reference designs is indeed very tempting. I think I will choose a 'phased' approach first making a simple cross connection board and, if that works, go for the full monty.

I like the idea of going for the ZIF connector. The original reason for the AAA batteries was that I can easily replace them en route, but indeed I can also carry a powerbank.

I am kind of hesitant to start soldering smd components but maybe I should watch a couple good video's on that too. Lots of inspiration!

Thanks again.

HenkJan

[becorey]

I'd recommend to layout a board with only smt parts, no through hole, then order the board from a board house like pcbway to do bare board fab and smt assembly. You can pm me if you want to work together. It's okay to put footprints for through hole headers but leave them off the bom, you can hand solder later. Then all the small smt is taken care of professionally. The lead time can be around 3-6 weeks and the cost is pretty cheap, like $50-$100 for 5 assembled boards. Cost all depends on the costs of your components, single or double side assembly, number of layers, board size, etc.

Honestly I would skip the middle step of doing layout for a "connection board", that sounds like an old school PWB (printed wire board) with no components just connectors. Its not much of an advancement beyond your first step of having wires go board to board with your proto modules. Work it out with proto boards, confirm the functionality, then the good next step is a pcb where you eliminate proto boards by putting the components from them directly on your pcb.

Here's the setup I'd recommend:

On the pcb:
Esp32 wroom or wrover module (wrover has more RAM, larger module)
Usb to serial chip, for programming the esp32
BMI-160 accelerometer
uSD card slot
USB connector
Battery charger IC
DC buck boost regulator (bring the li-ion 2.5V-4.2V to output 3.3V)

Connectors on pcb for off-board parts:
- Connector for your TFT/touch screen. Please share the link of the actual part if you already have something you like. There's tons of options for displays and touch screens. Generally the display needs a driver IC and the touch screen does as well. I'd recommend cap touch over resistive. And it's nicer to have the drivers integrated into the flex cable.
- 4 pin for BNS-180 gps, match the pitch of the connector on the module
- 2 pin JST for li-ion battery pack, common battery connector
- 2 pin for power switch, probably 0.1" pin header


https://easyeda.com/coreymberman/henkjan-gps