SIM900 and s/w or h/w conection


I want to connect the SIM900 module to the Arduino-UNO - for sending and receiving SMS messages (this is for giving commands to UNO and reading counter status from a distance).

I have been reading quite a few tutorials and got to some confusion :o Which serial interface should I use - the inherent hardware (pins 0-1) or to set a new s/w interface (and define 2 other pins)?

Thank you in advance!

A lot of people use software serial to save money, but there is NO substitute for hardware serial when your program grows more complex and becomes more interactive.

Software serial certainly works within strict limits, and let’s you use the USB serial for debugging, but bumping up to a MEGA 2560 or other processor with multiple UARTs is always a good thing when you’re working with serial data.

Thank you!

(Sorry for the late reply).

I got the SIMCOM-808 which has the GPS on it as well.

It also has an ON-switch, which requires an actual press for 1 second, or
Activation via the s/w interface.

H/W I/F requires only pins 0-1
S/W I/F requires 7-8-9

I don't have an extra pin for that - only 2 are available.

Any idea?

If the module you’re using has it, the power control pin is often brought out to the Arduino headers.
It’s a little bit fiddly, but read the datasheet for the timing to turn the module on.
Turning off is a software command - AT+CPOF

Good luck.
Keep in mind the 808 is a 2G module... its useful life in some countries is over, and probably 2-3 years in the rest of the world as 2G networks are closed down.
Australia for example has already scheduled the end of 3G in a few more years.

Thank you again!

Can you please explain your meaning - "power control pin is brought out to the Arduino headers" ?

I found a timing explanation to turn it on, but by using pin-9, which I want to use for a different thing (I don't have more than 2 pins available for the GSM module, therefore I am allocating H/W I/F with pins 0-1).

It is a good suggestion concerning 2G.
Here in Israel, where I am from, there is no sign yet for stopping 2G.
But they are moving very fast now with 5G - so who knows what happens then.