In the previous article we have briefly described the NB-IoT and LTE-M, their applications and possible challenges that you might encounter when trying to implement these technologies in your project. Today we are going to describe the basic hardware configuration of Waveshare modules Pico SIM7020E NB-IoT and Pico SIM7080G Cat-M/NB-IoT.
Testing the communication over UART
Pico SIM7020E NB-IoT
Pico SIM7080G Cat-M/NB-IoT
Hardware setup
The easiest way to test communication with the module is to use a USB-UART converter with an application for serial connection (such as PuTTy). Before we dive into proper PuTTy configuration let’s take a look at hardware connections
In both cases, USB-UART must be configured to the 3.3 V level of signal output (insert a jumper between appropriate pins)
SIM7020E
Pins from the Pico SIM7020E NB-IoT module need to be connected as follows:
- VSYS and GND connected to external +4V power supply (if you are not using the battery included with the Pico SIM7020E board). When trying to supply this pin from 3.3V it might work, but the communication may be unreliable.
- GPO0 (RXD) needs to be connected to the TXD pin from the USB-UART converter
- GPO1 (TXD) needs to be connected to the RXD pin from the USB-UART converter
- GND connected to GND pin from USB-UART converter
SIM7020E with USB-UART connections, images from Waveshare and Botland
SIM7080G
Pins from the Pico SIM7020E NB-IoT module need to be connected as follows:
- VSYS and GND connected to external +4V power supply (if you are not using the battery included with the Pico SIM7080G board).
- GP0 (RXD) needs to be connected to the TXD pin from the USB-UART converter
- GP1 (TXD) needs to be connected to the RXD pin from the USB-UART converter
- GND connected to GND pin from USB-UART converter
- 3V3 (OUT) connected to 3V3 (in the case of this USB-UART converter it was available on the PWR pin)
- GP14 (PWR) needs to be connected to GND, then to 3V3 for at least 1 second, then back to GND (as shown in the picture below)
- GP17 (DTR) needs to be connected to GND
SIM7080G with USB-UART connections based on images from Waveshare and Botland
PuTTy configuration
The application needs to be able to send a whole line of text in a single message. In PuTTy it can be done by setting Local echo and Local line editing options to Force on as presented below:
Communication with these SIM modules is achieved using AT commands. After sending each command according to the datasheet of a specific module. Most of the commands return either OK or ERROR (optionally together with other data specific for a command). Example commands that can be used to test communication with the module
(example response from the SIM7020 module printed with indent in italics).
ATI
SIM7020 R1752 OK
AT+GMI
SIMCOM_Ltd
OK
Summary
In this article we have presented how to connect and communicate with two SIM modules – SIM7020E and SIM7080G using USB-UART converter. We have described hardware connections and PuTTy configuration enabling us to send a receive simple commands confirming, that the module is working correctly. In the next article we are going to describe how to connect our modules with a test broker using NB-IoT connection. See you in the next article!
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