1. The computer can debug USB--TTL. The power supply of this module is: 5V-26V, 5V 2A power supply is recommended. After plugging in the Arduino board, the power supply must be able to provide 2A of current. The reason is that the power-on current and the peak current of the GPRS Shield require a maximum of 2A, but the USB port cannot provide such a large current, so an external power supply device must be connected.2.The other power supply port pin header leads out 3.7--4.5V power supply, which is suitable for lithium battery power supply. The serial port is perfectly compatible with arduino microcontroller. The TTL serial port is compatible with 3.3 and 5V microcontrollers. Make sure your SIM card is not locked3. The best baud rate for GPRS Shield communication is 19200 bps 8-N-1 (GPRS Shield defaults to automatic pairing baud rate) Note: This is the new version (64M version), supports SMS and MMS, the old version only supports SMS.4.The GPRS Shield is based on SIM900 module from SIMCOM and compatible with Arduino and its clones. The GPRS Shield provides you a way to communicate using the GSM cell phone network. The shield allows you to achieve SMS, MMS, GPRS and Audio via UART by sending AT commands (GSM 07.07 ,07.05 and SIMCOM enhanced AT Commands). The shield also has the 12 GPIOs, 2 PWMs and an ADC of the SIM900 module(They are all 2V8 logic) present onboard.Specifications: Application IdeasM2M (Machine 2 Machine) Applicatoions.Remote control of appliances.Remote Weather station or a Wireless Sensor Network.Vehicle Tracking System with a GPS module.CautionsMake sure your SIM card is unlocked.The product is provided as is without an insulating enclosure. Please observe ESD precautions specially in dry (low humidity) weather.The factory default setting for the GPRS Shield UART is 19200 bps 8-N-1. (Can be changed using AT commands).Interface Introduction: Power select-select the power supply for GPRS shield(external power or 5v of arduino)Power jack-connected to external 4.8~5VDC power supplyAntenna interface-connected to external antennaSerial port select-select either software serial port or hareware serial port to be connected toGPRS ShieldHardware Serial-D0/D1 of ArduinoSoftware serial-D7/D8 of ArduinoStatus LED-tell whether the power of SIM900 is onNet light-tell the status about SIM900 linking to the netUART of SIM900-UART pins breakout of SIM900Microphone-to answer the phone callSpeaker-to answer the phone callGPIO,PWM and ADC of SIM900-GPIO,PWM and ADC pins breakout of SIM900Power key-power up and down for SIM900.Material: PCB, metalcolour: bluePackage Contents:2 x SIM900 GPRS/GSM Shield Development BoardOnly the above package content, other products are not included.Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.