74ls24 is a four-channel dual-input non-Schmitt trigger. Its input has shaping and anti-interference functions. Because it is a TTL chip, the output current is small, so it can't drive a load with large current and high power. Uln2003 is a Darlington array composed of seven transistors, with an output current of 500Ma and a voltage of 50 V.. The output of 74ls24 is connected to the input of uln2003, so it can shape the load with high driving power after non-operation.