The relay board as the name implies, is a gadget build to interface two systems with different voltage levels and relay the signals from one system to another without signals (voltages) short circuiting. One of the more wide spread application in the industrial environment is picking signals from a low voltage programmable logic controller PLC (12 or 24Vdc) and interfacing the signals by use of relays to loads of medium voltage (240Vac).
However, apart from the industrial environment, the relay board has found a very fascinating use in the GSM industry. The relay board is now used to interface the alarm reporting signals on GSM split sites. (A split site is one built with the tower and Radio transmitting equipment installed on top of a steep hill, and the power sources (Genset) installed at the plainer bottom of the hill). The distance between could be up to 1Km. The interface relay board is used to pick alarms signals from the bottom of the hill to the transmitting equipment at the top of the hill. The signals are than transmitted to Monitoring centre of the mobile service provider. The relay board has among other features, status indication LED for easy of fault finding, and fast blow fuse for protection. The interface relay board comes in either 6 or 12 relays.