No SoftwareSerial without HardwareSerial?

Hi,

a have a Arduino pro mini (compatible) Board connected to a SIM800c module via Pin2/3 by using Software Serial. After some huddles with String-Variables the project works now perfectly when arduino is connected via USB to my PC an (normal) 5V Circuit is power on tool (because SIM800c needs more Power for sending)

But when i disconnect USB from PC the Serial Connection to SIM800C doesnt work work well. Unfortunally - i'm a little bit blind without Serial prints.

Anybody can help me? can it be an electrical problem (Add Info: connect the USB to a powerbank doesnt work too)

Thanks for any tip

Something does not make sense; a pro mini does not have a USB port.

Indeed a Pro Mini does not have a USB port, and the average USB to serial adapter, which you would use to program a Pro Mini, is quite poor as a 'power supply'

if you disconnect usb, how do you power pro mini ?

Sorry for bad intendation. Its not an Pro mini (so i wrote "compatible") My module has an USB/Serial onboard

it's this:

https://i.stack.imgur.com/FbDGT.jpg

Looks like a Nano to me

ludiwawa: can it be an electrical problem

Almost certainly, and a dire shortage of watts springs readily to mind. The exact problem is far from clear and probably depends on what you mean by

doesnt work work well.

You seem to imply that the USB port is your salvation, whereas I would have thought that, as far as power is concerned, the opposite would have been more likely.

I don't understand why these things hog so much power, but I do understand you need a decent power supply with 5v 3A, one for Nano and two for the phone. I don't understand why you want to disconnect USB anyway. It seems self-defeating, but I'm sure you shouldn't rely on it for power.

UKHeliBob: Looks like a Nano to me

you're right - but unfortunally when i use Board "Ardunio Nano" in IDE i cant upload my sketch. there are errors like "avrdude: stk500_recv(): programmer is not responding avrdude: stk500_getsync() attempt 1 of 10: not in sync: resp=0xac avrdude: stk500_recv(): programmer is not responding avrdude: stk500_getsync() attempt 2 of 10: not in sync: resp=0xac avrdude: stk500_recv(): programmer is not responding"

when i select "Arduino Pro mini" this works fine.

Which processor have you got selected in the IDE with the board set to Nano ? Have you tried the “old bootloader” option ?

UKHeliBob: Which processor have you got selected in the IDE with the board set to Nano ? Have you tried the "old bootloader" option ?

ah ok, this works. i didn't seen this. Whatever - the Problem is the same. everything works while USB is connected - when disconnect USB Communication between sim800 and arduino is confused

How is it powered when the USB is disconnected ? You didn't answer when asked previously

UKHeliBob: How is it powered when the USB is disconnected ? You didn't answer when asked previously

oh sorry - i have an 5V 2A Power Supply connected to 5V/GND of Arduino (not VCC) and 5V/GND of sim800c

This Power-Supply is connected even when USB ist attached...

In that case it sounds like 5v 2A isn't enough, and it is actually dependent on some extra from the USB cable.

I guess "Arduino is confused" is in the same category as "doesn't work well" - and somewhat meaningless.

In the light of

Unfortunally - i'm a little bit blind without Serial prints.

I won't bother asking again why you want to disconnect the USB cable.

Nick_Pyner: In the light ofI won't bother asking again why you want to disconnect the USB cable.

Because the arduino with sim800c should work standalone?

ludiwawa: oh sorry - i have an 5V 2A Power Supply connected to 5V/GND of Arduino (not VCC) and 5V/GND of sim800c

This Power-Supply is connected even when USB ist attached...

That is not good idea IMHO, two things try to keep that line at their impression of 5V. I use a modified USB cable with switchable 5V in such cases.

Whandall: I use a modified USB cable with switchable 5V in such cases.

This is a great idea - i will build one.

PROBLEM SOLVED!

Everythink works fine with an pulldown resistor (4k7) on RX Line of sim800c (Pin D2 on my Arduino). I don't know why it works when USB is connected ...

Thanks to all