@felmue USA... and I ordered t-mobile,, should be in later this week, there is a lot of snow here. I also asked Soracom, but they told me it will not work here... I'll keep you posted. I really like the Atom DTU; there could be a more global modem in there... or perhaps a few to choose from.

@felmue It seems that this M5Stack ATOM DTU is not very usable in only a few countries as this overview:
https://developers.soracom.io/en/docs/reference/carriers/ shows very few countries support NB-IOT;
looking for a modem now that supports LTE-Cat M1 as that is more a global solution. Bummer, as I really like the form factor combined with the RS485 interface; perhaps another modem in the future? I ordered a sim card from T-Mobile for NB-IOT (took me a better part of ther day, I'll report back how that goes; according to their business web site they are the leader in NB-IOT; hopeful.

@felmue Got hologram not to work yet, it does see a number of providers but does not register, I asked support @hologram. They had a special for sim7000 but that is not compatible with the 7020G.. bummer. I bought another sim, now Soracom, arriving Tuesday, hope that goes better... I studied up on MQTT though and have that knowledge now, ready to deploy ;-)

@felmue Using Hologram, from my research the best, have good signal but no ip communication yet, I am a weekend warrior ;-)

@felmue thank you for your help.

I found my problem, very basic first line should read:

Serial2.begin(115200, SERIAL_8N1, G19, G22); //TX to RX and RX to TX

I first wanted to have basic access to AT commands, making sure my sim card was inserted correctly, what my signal strength is, setting of my APN, etc. I used to program in assembler, after that higher language and checking the compiler output... I like to know what is actually happening.

By the way, I used PuTTY as my terminal emulator as it works better than the IDE from Arduino for this purpose, Arduino composes a line before transmitting and PuTTY does it each character as you type. Also, the reset connection works like a charm if disconnected.

(yes, the way the sim card needs to go in is opposite of normal, the slant corner on the outside and the contacts up.)

program I use to connect to the sim7020:

#include <HardwareSerial.h>

void setup() {
// put your setup code here, to run once:
Serial.begin(115200);
// set the data rate for the HardwareSerial port
//Serial2.begin(115200);
Serial2.begin(115200, SERIAL_8N1, G22, G19);
}

void loop() {
if (Serial2.available()) {
Serial.write(Serial2.read());
}
if (Serial.available()) {
Serial2.write(Serial.read());
}
}

The program works when G19 and 22 are connected, but inserted I get no reply to AT.

Powered with 24V made no difference, what to check? I also tried to change rx and tx but did not make a difference.

TIA, Robert.