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LILYGO T-SIM A7670E: an ESP32 and an LTE modem on one board

Bench build · Bench builds · Intermediate · about 60 minutes

ESP32-WROVER-E + SIMCom A7670E LTE Cat-1 board: power-on sequence, registration, data context, BAT_ADC. Commercial IoT boards fuse a microcontroller, a radio and a power front-end on one PCB. On the T-SIM A7670E the ESP32 talks to the A7670E modem over an internal UART (Serial1, RX GPIO27, TX GPIO26), switches the modem’s supply with GPIO12 and presses its power key with GPIO4. The modem does not start by itself: the sketch must switch it on, pulse PWRKEY and poll AT. Its supply hangs on the 18650: on USB alone the 2 A bursts of a 2G transmission pull it under 3.3 V and it browns out.

LILYGO T-SIM A7670E: an ESP32 and an LTE modem on one board: the finished build running on the simulator's bench

Build it in the labGuided build, test sheet and fault finding, free in your browser.

Parts list

Test procedure

Each test has an expected value and a pass range, like a factory test sheet:

  1. VBAT from the 18650
  2. BAT_ADC (GPIO35) is half of VBAT
  3. Modem answers AT
  4. Registered on LTE

How it works

What it does: ESP32-WROVER-E + SIMCom A7670E LTE Cat-1 board: power-on sequence, registration, data context, BAT_ADC.

Build it (guided or ready-made), then run its test procedure below. Every test has an expected value and a pass range, just like a factory test sheet.

Background

The hardware behind most hobby and commercial cellular trackers.