Hi,
I have connected it directly to my laptop and used SSCOM to send AT commands and have successfuly sent myself a text message.
These are the commands I used in SSCOM
AT
AT+CMGF=1
AT+CMGS="+61412345678" (Not my real number, just a dummy for this post)
Test
HEX (1A)
That successfully sends a msg of "Test" to myself via sms. This was all done at a baud of 9600.
Now I want to do the same but use the arduino to send the informaton to the SIMCOM7600 module and this is where I need help.
The product states that the uart is ttl 3.3v.
I understand the leonardo is 5v, and therefore I need to convert the Tx pin on the arduino, down to 3.3v levels.
I have whipped up a voltage divider containing:
- two, 1k resistors in parralel to make a 0.5k resistor
- Connected it in series to a single 1k resistor
- Powered the SIM7600 with a lab power supply (set to 5v)
The wiring looks like this:
The green blinking LED that indicates a positve network connection, starts blinking after about 15 seconds of providing power from the lab power supply.
Very simple program, just sending "AT" to see if I get the "OK" response.. I do not. Program below.
int x;
void setup() {
x=0;
Serial1.begin(9600);
Serial.begin(9600);
delay(3000);
}
void loop() {
Serial1.println("AT");
delay(100);
while (Serial1.available()>0){
Serial.print(Serial1.read());
}
delay(10000);
x=x+1;
Serial.println(x);
}
Most of the time there is silence, sometimes I get gibberish like a square or an O with '' at the top or y with '' at the top etc.
My first thought was baud rate, so I tried all the 'standard' baud rates up to 115200. Same response or no response. So I disconnected the SIM7600 from the arduino and plugged it directly back into the computer. Then by using SSCOM, I sent the command to set the baud rate, set it to 9600 and the removed it from the computer again. Re-connected the cables again but no change in outcome.
Something weird is obviously going on in the serial communication. It could be due to my voltage divider, but I have a different 3.3v uart device that works with my voltage divider so its not total crap. And I tested the voltage coming out of the voltage divider with a multimeter, it is indeed 3.3v.
I could try software serial but that sounds like a dumb move.
on the SIM7600 board it says "URX" and "UTX". I'm assuming they're equivalent to Rx and Tx and there's nothing particularly special about the "U"? /I've no idea what the U means in this case.
Do you guys have any ideas I could try?
Thanks in advance