communication between arduino and sim900 via softwareserial

hello ,

i have this weired problem connecting an arduino uno to sim900 via softwareserial.

if i hook up rx and tx of the sim900 to the hardware serial of arduino (pin0,pin1)and i wire reset of the board to gnd , and use Hterm to communicate to sim900 : averything is good , i can make calls send sms , receive sms and feedback from sim900.

now , if i hook up sim900 to softwareserial , let say 9 and 10 ,and i use a code to send AT commands to sim900 via softwareserial ,let say : ATD06xxxxxxxx; , the first commands execute fine , and i have a feedback , but the second one is bad .
here is an exemple :

assume i send ATD06xxxxxxxx;

ATD06xxxxxxxx;

OK

(i hang up i receive this instead of BUSY)
i$Z⸮R⸮(⸮

ATD06xxxxxxxx;

A⸮鷙{̚1⸮

i have to power off/on the sim900 to accept communication , and it seem that the second command get scrambled before it is send to the sim900.

now if i use arduino to communicate to the sim900 via hardware serial ( usb unplugged) it work fine , i can execute as many AT commands as i want.but i can not debug via serial.print

i use arduino 1.8.9

thank you

i hook up an ftdi to software serial , send text to software serial and monitor on my pc . the software serial is the probleme , maybe the arduino board . it's a 12Mega clone.

sunivers:
the software serial is the probleme ,

Quite possibly, but hard to tell because of your paranoia about showing your code. You can almost be sure it is user error, rather than blaming the Mega and, if it really is a Mega, one would wonder why on earth you are using software serial in the first place.

all is good now ,

i use AltSoftSerial intead of softwareserial.

now everything is fine

thank you for the reply

[/quote]

Nick_Pyner:
Quite possibly, but hard to tell because of your paranoia about showing your code. You can almost be sure it is user error, rather than blaming the Mega and, if it really is a Mega, one would wonder why on earth you are using software serial in the first place.

it's not a Mega board , it's a clone of uno board at 12 megahertz

sunivers:
it's not a Mega board , it's a clone of uno board at 12 megahertz

But remember you said;

"it's a 12Mega clone"

ans i Saïd in the first post its an arduino uno , to not repeat that I said it's a 12mega clone meaning hertz .