# SIM800C GSM modem: specs and pinout

> A quad-band GSM/GPRS modem built around the SIMCom SIM800C module. It takes AT commands over a serial port to send SMS, make voice calls and open…

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A quad-band GSM/GPRS modem built around the SIMCom SIM800C module. It takes AT commands over a serial port to send SMS, make voice calls and open GPRS data links. The maker's document covers the SIM800C module only, not this carrier board.

Every value cites its sourceChip-level pinout

[Buy on Compoden](https://compoden.com/products/gsm-sim800c-modem-with-antenna)

## Specs

| Spec | Value | Source |
|---|---|---|
| Power supply (VBAT) | 3.4 V to 4.4 V, recommended 4.0 V | source Section 4.1 Power supply; Table 2 SIM800C key features |
| Transmit burst current | Supply must provide up to 2 A; peak 2.0 A during transmit burst | source Section 4.1 Power supply; Table 34 current consumption, peak current |
| Minimum VBAT during burst | Must not drop below 3.0 V; module may shut down below 3.0 V | source Section 4.1.1 Power supply pin |
| Frequency bands | GSM 850, EGSM 900, DCS 1800, PCS 1900 | source Table 2 SIM800C key features |
| Transmit power | Class 4 (2 W) at GSM 850 and EGSM 900; Class 1 (1 W) at DCS 1800 and PCS 1900 | source Table 2 SIM800C key features |
| Serial interface | UART, autobaud 1200 to 115200 bps; 8 data bits, no parity, 1 stop bit | source Table 2; autobauding section |
| Operating temperature | -40 C to +85 C normal operation | source Table 2 SIM800C key features |
| SIM card | 1.8 V and 3 V SIM cards | source Table 2 SIM800C key features |

## Power

| | Value | Source |
|---|---|---|
| Supply | 3.4 V to 4.4 V on VBAT; the supply must hold at least 3.0 V during 2 A transmit bursts (the maker suggests a 100 uF low-ESR capacitor plus 1 to 10 uF ceramic at VBAT) | source Section 4.1 Power supply; Table 34 |
| Current | Up to 2.0 A peak during a transmit burst | source Section 4.1 Power supply; Table 34 |

## Chip pins
These are the pins of the chip on the module, from the chip datasheet. The module's own header may label or expose them differently.

These are the SIM800C module's own pins from SIMCom's Hardware Design document. The modem board's header order, regulator, signal level shifting and any USB or RS232 side are not covered by an official document. The document used is V1.02; a later revision may change figures.

| Pin | Function | Voltage | Notes | Source |
|---|---|---|---|---|
| VBAT (34, 35) | Power supply | 3.4 V to 4.4 V | Two pins | source Table 5 pin description |
| GND (8, 13, 19, 21, 27, 30, 31, 33, 36, 37) | Ground | 0 V | | source Table 5 pin description |
| PWRKEY (39) | Power on / power off input | | Pull low at least 1 second and release to power on or off | source Table 5; section 4.2 |
| UART1_TXD (1) | Serial transmit (module output) | | | source Table 5 pin description |
| UART1_RXD (2) | Serial receive (module input) | | | source Table 5 pin description |
| VDD_EXT (40) | 2.8 V power output | 2.8 V | | source Table 5 pin description |
| NETLIGHT (41) | Network status output | | | source Table 5 pin description |
| STATUS (42) | Power-on status output | | | source Table 5 pin description |
| GSM_ANT (32) | GSM antenna connection | | 50 ohm | source Table 5; section 4.13.1 |

## Build with it
Project ideas for the SIM800C GSM modem. Each link opens Soldr with the prompt filled in; Soldr assigns the pins, checks power and shows how to wire every part.

- [Cellular signal and battery readout](https://app.soldr.ai/?prompt=I%20want%20to%20build%20a%20GSM%20battery%20voltage%20readout%20with%20an%20ESP32%2C%20an%20OLED%20display%20and%20a%20SIM800C%20modem): Learning project: AT+CBC reports the VBAT voltage. The module's VBAT range is 3.4 V to 4.4 V, so a single cell (4.2 V full) fits only if the carrier board takes a raw cell, which is not documented here; confirm that first. The supply must give 2 A bursts without dropping under 3.0 V: the 30C cell through a 3 A protection board can, a USB port or the ESP32 board's pin cannot. The ESP32 runs from its own USB supply with a shared ground. Fit the antenna before power-up and use a valid SIM.
- [Temperature text message reporter](https://app.soldr.ai/?prompt=I%20want%20to%20build%20a%20temperature%20text%20message%20reporter%20with%20an%20ESP32%2C%20a%20waterproof%20DS18B20%20probe%20and%20a%20SIM800C%20modem): The ESP32 reads the probe and sends the reading as an SMS through the module over the serial port. The module's serial pins are about 2.8 V logic in the maker's reference circuits, so add the divider the sheet shows (1 k in series and 5.6 k to ground on the line from the ESP32 TX to the module RX) unless the carrier board already handles it. Same 2 A burst supply rule as above: single cell through the protection board, ESP32 on its own USB supply. Learning project; needs a SIM with SMS.
- [Text-controlled LED](https://app.soldr.ai/?prompt=I%20want%20to%20build%20a%20text-controlled%20LED%20with%20an%20ESP32%20that%20reads%20incoming%20messages%20from%20a%20SIM800C%20modem%20and%20switches%20an%20LED): The ESP32 polls the module for new SMS text and lights an LED through a series resistor from the ESP32 board. The module runs from the single cell through the protection board (2 A burst, never below 3.0 V), the ESP32 from its own USB supply, with a shared ground and the serial divider noted above. Fit the antenna first. Learning project.

## Common mistakes

- Powering the module from a USB port or a small board pin: the maker says the supply must deliver up to 2 A in transmit bursts and VBAT must not fall below 3.0 V, otherwise the module can shut down (source: [link](https://www.elecrow.com/download/SIM800C_Hardware_Design_V1.02.pdf), section 4.1)
- Transmitting without an antenna fitted: the module has a GSM antenna pin (GSM_ANT, pin 32) for the GSM antenna, so fit the antenna before powering up (source: [link](https://www.elecrow.com/download/SIM800C_Hardware_Design_V1.02.pdf), section 4.13.1)
- Wiring a 3.3 V host serial pin straight to the module: the maker's reference circuit for a 3.3 V host puts a 1 k resistor in series and 5.6 k to ground on the line from the host TX to the module UART1_RXD (source: [link](https://www.elecrow.com/download/SIM800C_Hardware_Design_V1.02.pdf), serial interface section, Figure 19); check the carrier board's own signal level before wiring

## Not covered by the official source

- Carrier board (voltage input, regulator, serial level, connectors) has no official document; the ideas power the bare module's VBAT range from a single cell and say to check the carrier first.
- Only revision V1.02 (2015-04-27) of the Hardware Design was available as a verbatim copy; SIMCom's own site needs a login to download.
- Page numbers not recorded; section names cited instead.

## Sources

- [link](https://www.elecrow.com/download/SIM800C_Hardware_Design_V1.02.pdf) (SIMCom SIM800C Hardware Design V1.02, 2015-04-27; maker: SIMCom)