1. The computer can debug USB--TTL. The supply of this module is: 5V-26V, 5V 2A supply is recommended. After plugging in the board, the supply must be able to 2A of current. The reason is the -on current and the current of the GPRS Shield require a maximum of 2A, but the USB port cannot such a current, so an external supply device must be connected.2.The other supply port pin header leads out 3.7--4.5V supply, which is suitable for lithium battery supply. The serial port is perfectly compatible with microcontroller. The TTL serial port is compatible with 3.3 and 5V microcontrollers. Make your is not locked3. The best baud rate for GPRS Shield communication is 19200 8-N-1 (GPRS Shield defaults to automatic pairing baud rate) Note: This is the new version (64M version), supports SMS and , the old version only supports SMS.4.The GPRS Shield is based on SIM900 module from SIMCOM and compatible with and clones. The GPRS Shield provides you a way to communicate using the GSM cell phone network. The shield allows you to achieve SMS, , 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 or a Wireless Sensor Network.Vehicle Tracking System with a GPS module.CautionsMake your 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 8-N-1. (Can be changed using AT commands).Interface Introduction: select-select the supply for GPRS shield(external or 5v of ) jack-connected to external 4.8~5VDC 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 Software serial-D7/D8 of Status LED-tell whether the 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 SIM900 key- up and 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. Note: Due to the light and screen setting difference, the item's color may be slightly different from the pictures. Please allow slight dimension difference due to different manual measurement.