TTGO T-Call ESP32 + SIM800L: specs and pinout
LilyGO T-Call board: an ESP32 module wired to a SIMCom SIM800L GSM/GPRS modem, with a USB-UART bridge and an IP5306 battery charger/boost chip on the IP5306 revisions. The listing does not name a hardware revision (LilyGO documents v1.3 and v1.4), so this page uses only facts that hold for both, and marks the v1.4-only pins.
Specs
| Spec | Value | Source |
|---|---|---|
| GSM modem supply (SIM800L VBAT) | 3.4 V to 4.4 V (recommended 4.0 V) | source One-page SIM800L sheet, General features; SIM800 Hardware Design V1.08 section 4.1 (p.20) |
| GSM modem peak current | Supply must deliver up to 2 A during transmit bursts | source SIM800 Hardware Design V1.08, section 4.1 Power Supply (p.20) |
| GSM bands | Quad-band 850 / 900 / 1800 / 1900 MHz | source One-page SIM800L sheet, General features |
| GPRS data | GPRS class 12, up to 85.6 kbps | source One-page SIM800L sheet, Specifications for GPRS Data |
| Modem operating temperature | -40 to 85 C | source One-page SIM800L sheet, General features |
| SIM card voltage | 1.8 V and 3 V SIM cards supported | source SIM800 Hardware Design V1.08, Table 1 key features (p.10) |
| Modem sleep current | 1.2 mA typical (AT+CSCLK sleep, BS-PA-MFRMS=9) | source SIM800 Hardware Design V1.08, Table 1 (p.10) |
| IP5306 I2C slave address | 0xEA (8-bit form), up to 400 kbps | source IP5306 register document V1.21, section 1 I2C (p.1) |
| 5 V pin on IP5306 versions | Output boosted by the IP5306 (max output current 2.4 A per LilyGO); with the AXP192 version it is an input | source README FAQ 2, About the 5V power pin description |
Power
| Value | Source | |
|---|---|---|
| Supply | USB input and a lithium battery on the IP5306 revisions (IP5306 charges and boosts); the SIM800L itself needs 3.4 V to 4.4 V at up to 2 A peak | source SIM800 Hardware Design V1.08, section 4.1; LilyGO README FAQ 3 |
Pinout
Pin rows come from the LilyGO repo pin table, which covers v1.3 and v1.4; rows marked v1.4 only do not exist on v1.3. The schematic used is the 20200811 one (v1.4, sheets 1-3), so the stocked revision is not confirmed and the full header list is not given. The SIM800L figures come from SIMCom documents hosted in the same LilyGO repo.
| Pin | Function | Voltage | Notes | Source |
|---|---|---|---|---|
| IO26 | Modem TX (modem TXD to ESP32 receive) | v1.3 and v1.4 | source Pin definition table; schematic sheet 3 (GSM_TXD to IO26) | |
| IO27 | Modem RX (ESP32 transmit to modem RXD) | v1.3 and v1.4 | source Pin definition table; schematic sheet 3 (IO27 to GSM_RXD) | |
| IO4 | Modem PWRKEY | v1.3 and v1.4 | source Pin definition table | |
| IO5 | Modem RST | v1.3 and v1.4 per table; in the 20200811 schematic the series part on this line (R114) is marked NC | source Pin definition table; schematic sheet 3 | |
| IO23 | Modem power (enable of the modem supply regulator) | v1.3 and v1.4 | source Pin definition table (MODEM POWER); schematic sheets 1 and 3 (IO23 to regulator EN) | |
| IO21 | Power chip SDA (IP5306 I2C) | v1.3 and v1.4 | source Pin definition table | |
| IO22 | Power chip SCL (IP5306 I2C) | v1.3 and v1.4 | source Pin definition table | |
| IO32 | Modem DTR | v1.4 only (not present on v1.3) | source Pin definition table | |
| IO33 | Modem RI | v1.4 only (not present on v1.3) | source Pin definition table | |
| IO13 | On-board LED | v1.4 only; README: blue LED on GPIO13 | source Pin definition table; README FAQ 6 |
Build with it
Project ideas for the TTGO T-Call ESP32 + SIM800L. Each link opens Soldr with the prompt filled in; Soldr assigns the pins, checks power and shows how to wire every part.
- A remote temperature and humidity SMS reporter with a TTGO T-Call and a DHT22 sensor: The T-Call has the modem and the ESP32 on one board; the DHT22 module runs from the 3.3 V pin and needs one free GPIO. Needs a SIM card with SMS and 2G network coverage where you live; a learning project.
- A water tank float alert that sends an SMS when the level changes with a TTGO T-Call and a float switch: A float switch is a dry contact, so it can pull one ESP32 GPIO to ground (use the internal pull-up) and wake the board to send a text. A learning project, not a flood-safety system.
- A GPS location texter for my own bike with a TTGO T-Call and a NEO-6M GPS module: The NEO-6M talks over a serial port to a spare ESP32 UART while the T-Call sends the position by SMS. Track only your own property; keep the board on a battery plus USB supply that can handle the modem's 2 A peaks.
Common mistakes
- Powering the board from a weak USB port or thin cable: the SIM800L needs up to 2 A peaks, and LilyGO says dropouts and sudden shutdowns are usually from insufficient USB current and recommends connecting a lithium battery as well (source: link, FAQ 3; link, section 4.1)
- Expecting a battery-only board to start by itself on IP5306 versions: LilyGO says you must press the reset button to switch on (source: link, FAQ 4)
- Swapping the modem serial pins: the LilyGO table says MODEM TX is IO26 and MODEM RX is IO27, naming them from the modem side; in the schematic IO26 receives the modem TXD line and IO27 drives the modem RXD line, so in your code ESP32 RX = 26 and ESP32 TX = 27 (source: link; link, sheet 3)
Not covered by the official source
- The listing does not give the board revision. LilyGO's repo lists v1.3 (2019) and v1.4 (2020, the one on the current product link); facts not common to both revisions are marked.
- The schematic shows an ESP32-WROVER module and a CP2104 USB-UART bridge on v1.4; the ESP32-WROVER module datasheet is not covered here, so no ESP32 supply or flash/PSRAM figures are given.
- SIM800 logic levels at the modem pins are not given because the board adds transistor level shifting that the documents do not describe.
- The AXP192 power variants (separate LilyGO schematic) are not covered.
Sources
- link (LilyGO T-Call SIM800L IP5306 schematic, 2020-08-11, 3 pp)
- link (LilyGO doc SIM800L IP5306, pin table for v1.3 and v1.4)
- link (LilyGO T-Call SIM800 series README, FAQ)
- link (SIMCom SIM800 Hardware Design V1.08, 2015-03-05; hosted in the LilyGO repo)
- link (SIMCom SIM800L one-page sheet V1005; hosted in the LilyGO repo)
- link (IP5306 register document V1.21; hosted in the LilyGO repo)