Control of schematic before PCB, ATmega, LoRa, GSM, HX711

Projects General Guidance
1

Hi

I have a schematic that is not built yet. I will do a final control and ask you guys on this forum to get feedback.

In general:
Can I ask for your comments regarding pins used to communicate between ATmega and modules?

Specific:
I need possibility to have both LoRa and GSM on my project, options is to use either LoRa or GSM, or both at the same time.

So the question is if this is a possibility with ATmega?

Pins:
LoRa to 16, 17, 18, 19 on ATmega
GSM to 2, 3 on ATmega

Thanks up front!

Circuit:

image
image661×1001 90.6 KB

2

Since your using a 28 pin DIP ATmega328P, its not difficult for you to breadboard the circuit before you design the PCB, its much easier to correct design issues on a breadboard versus a finished PCB.

But dont wire up even a breadboard as per the schematic, you stand a chance of destroying stuff.

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3

if you are using a RA-01 LoRa module you will need to conect RST and DIO0 and possibly DIO1 (depends on LoRa library used)
the Atmega328 uses 5V logic the RA-01 uses 3.3 V logic - you will require level converters

GSM modules can draw up to 2 amps when transmitting - make sure your power supplies can supply this

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4

Hi

Thanks for answer!

I will build it on a breadboard, but I wanted to ask if the pins I have choosed for LoRa and GSM is possible to use and also run simultaniousy.

5

Not when powered by 3.3V, as shown.

6

There is a LoRa library that will run on the connections shown, but most of them need at least one more, possibly two pins connected. Check the pin requirements of the library you are using.

The voltage supply, to the ATMega328P and LoRa device looks like its a Lithium battery, since its labelled as 3.7v, If its a lithium battery, that could be 4.2v. What is the maximum voltage for the LoRa module you are using, you will find that information in the devices datasheet ?

What does the ATmega328P datasheet say is the minimum working voltage for a 16Mhz crystal ?

7

Thanks for helping me @srnet

  • I plan to use a 3.7 Li-battery, I also use 5v to hx711 with a DCDC converter.
  • 16MHz I will check regarding voltage, but I have 5 V from converter but that is anoption I dont like due to my low power demand. I will switch off as many modules as possible with the mosfet and switch on to send data each 2 h
  • LoRa module max 3.6V:
    image
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Which will actually be 4.2V fully charged ..................

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Which will actually be 4.2V fully charged ..................

Thanks, this has been forgotten...

ai ai, I must add one more voltage regulator.

10

usually there is a small value resistor between the MCU pin and the gate... at the blue dot:
image

image
Figure above courtesy of @LarryD

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11

I wonder if you need a mosfet for power switching. Don't all but the DS18B20 have sleep modes? And the DS18B20 doesn't draw much, so just power it from a 328P pin.

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