Automatic fan for fire draught - has photoresistor sensing radiation from fire to control switching of fan motor

摘要

The automatically controlled fan for a barbecue or other fire includes a helical blade driven by a small electric motor. This is mounted with its axis inclined slightly below horizontal at the top of a moulded tapering body. The body is mounted on a rigid base plate. In front of the body of the fan there is a photoresistance sensitive to radiation falling on it. This photoresistance forms a potential divider along with a 220k variable resistance. The common point of the two resistances is connected to the base of a first transistor. This is connected in turn to a second transistor which controls the switching of current through the motor fan. The device is placed in front of a fire and provides additional draught when the radiated light falls below a certain level.