In view of the problem that the existing resistive sensor conversion circuit design mostly adopts the bridge circuit and its circuit structure is complicated, the design idea that the bridge circuit can be replaced with a very simplified circuit in certain application scenarios is proposed. By comparing and emulating these two types of circuits, it is pointed out that extremely simplified circuits can also meet the application of most scenarios with the continuous improvement of microprocessor performance and analog-to-digital conversion circuit resolution. So that the cost of raw materials can meet the requirements of functional performance. Then, push to a lower limit under the circumstances. On this basis, an optimal device selection method for extremely simplified circuit of fixed-value resistors is proposed. Finally, the actual bluetooth thermometer project is used for development and design . The test data shows that the temperature measurement error is less than or equal to 0.1℃, which meets the requirements of national standards.