1. This board needs to cooperate PI3, orange pie, a variety of school development board to use 2. This board has been applied in the GM300 GM3188 3688 950I 338 -1X, other types of repeaters and car stations need to be studied yourself The is intended to be an open-source Multi-Mode Digital Voice Modem, which utilities the power of an ARM processor and a simple analogue interface board. The Multi-Mode Digital Voice Modem is a combined hardware and software development of a modem to handle all amateur digital voice modes. Initially it support D-Star and DMR, with System Fusion and P.25 later, as well as a built-in FM repeater controller. For all modes other than DMR and FM, the modem can be used in simplex or duplex mode, while for DMR and FM full duplex must be used. After Connect GM3xx ,GM950i is better,when power on,LED Flash fast,if your MD380 PTT ,COS LED ON,so,decode is ok,then you must SEE the BER using DEBUG Port,or in pi-star panel,ADJUST RX_R BER is less than =2%,Then Test in Parrot you can hear your voice and PTT LED ON ,testing is Finished! It is Very Easy,I Testing Many Times. FAQ:what MODE you Tested ? DMR or or P25 I tested is the same. FAQ:Does test Using MMDVMCal Program?If You Tested Fail, Using MMDVMCal To Test GM3XX TX- Mobile Function. GM3XX RX- Function It is Easy To Check Just COS(RECEIVE SIGNAL) LED And MODE LED,if Both LED ON ,GM3XX Rx is work! FAQ:Does to change .ini -TX Invent and RX Invent?that is Also Import,in MMDVMCal TX Testing Mode you can I to Invent TX to Your GM3xx is invent or not . TESTED:GM950i TX Invent =0,RX Invent=0 BEST for Test is GM338 and GM950i ,GM300 TX Freq is not stable ,rx is ok GM300 need set inside Jumper to Disable 300HZ and 3000HZ filter. GM950i need set RX AUDIO(FLAT(UNSQUELCHED)Accy Pin 11,and GP1 PTT LOW 3(I/P) in GP I/O Lines 1.Support 5V microusb Power input(1A) 2.Support OTG Function 3.Support wifi client mod