Hello everyone!
I'd like to build a sort of "mini computer" that connects to smartphone via Bluetooth and receives various data from the custom Appinventor App I've made.
Now, I'm using a Seeeduino XIAO and I'm powering it with a 1.5 V AA 2700 mAh rechargeable battery and its voltage is increased to 5V through this step up module
At the moment, these sensors/modules are attached to the board:
1x Modulo RTC I2C
1x VL53L0X I2C
1x HC-05
But I would really like to use this Display Touch TFT LCD Nextion
Altough that display brings some questions I haven't been able to answer for my specific circuit:
1)Can both Display and HC-05 use the same TX and RX pins? or should I use two more I/O pins to separate them? (I'd use SoftwareSerial library)
2) Since Seeeduino has 3.3 V logic would there be problems if I attach the 5V and GND pins of the Display directly to the 5V and GND pins of the Seeeduino? Alternatively I was thinking about connecting the power pins of the display to the V0 e GND pins of the step up module (if it makes sense)
3)Is the battery currently chosen suitable for the project? To be sure can I measure current draw from the battery by connecting a multimeter in series to the + side of the battery and Vin of the regulator? I'm not really into using LiPo as I don't want them to explode so I stick to classic batteries
I've also added here a drawn schematic of the circuit, to hopefully be clear in explaining my doubts
Tx and Rx do not share well, use another set of pins. Good luck measuring the current draw, most multimeters add a resistor in series with the load and measure the voltage drop across that resistor which will also lower the voltage to your converter causing it to draw more current and reach its dropout threshold much faster if it even works. Your pictorial did not help, schematics are much easier to read then picture problems.
Sadly not all of the components are available in schematics softwares so I didn't have choice..
How about the display? Would it work if direclty connected to the Seeeduino XIAO?
I would suggest looking at a schematic capture such as KiCad, you are looking for pictures, most all parts are available in schematic capture libraries and if not you can make them. If you look you will find many resistor schemes to interface 5V to 3V, Ignore them they are working on the edge of the hardware logic levels, use a level converter, it is much more reliable and not very expensive.
One item per serial port, i.e. use software serial for a second as you propose. I understand your Arduino is 5v, but HC-05 is a 3.3v device, so it would be wise to use a 1k/2k voltage divider on Arduino Tx pin. In the matter of Bluetooth, you might find the following background notes useful.
Nooooo.. never a screen capture, the CAD programs have an EXPORT function, usually under the FILE tab.
An export will make an image file with FULL resolution.
A screen capture will make an image in the resolution of the screen. Usually pity fully poor if the CAD is very complex/large.
Interesting, must be the first time I see a display using UART Serial. Normally displays use a much faster and more reliable ISP connection to communicate.
And no, you generally can not share Tx/Rx lines. The protocol is not designed for this.
I wonder why everyone is so upset about LiPo batteries exploding... I take it you also don't use a modern mobile phone or laptop then? Those contain LiPo batteries, as do so many other common consumer products. Just get a battery with protection circuit from a reputable seller, not the bottom bargains from China. Chances are all your devices can run off the LiPo battery voltage directly (check data sheets). That alone makes your circuit much simpler.
@TomGeorge and @wvmarle, it's good to explain better why I've chosen those components
About the battery: it powers the Seeeduino (which is 3.3v logic by the way) but also powers a totally different circuit and that circuit can only be powered with 1.5V AA or AAA batteries
I have spare 3.7V LiPo batteries around but their capacity is not more 200-300 mAh... wouldn't last long and the second circuit can't be powered by those.
About the screen: yes, I know it can be programmed separately from the board and I've read it has to be done in order to load the code inside of it (both SD card or USB-TTL cables are fine for what I've read)
but most importantly it only uses 4 pins! and the Seeeduino is extremely small and doesn't have lots of pins.
I've forgot to say that wouldn't be a proper PC but more like a smartwatch so it will be portable..
Hopefully this has cleared the situation a bit more
