week 3

This week we made a profound improvement. We made a really significant discussion that we decided to change the chip of the drive circuit, which means we had to re-design the circuit and re-build it. There were serial reasons support us to change the H-bridge.

Firstly, the old circuit did not connected well. There was an open circuit in the circuit, however, after testing at each point, the cause was still unclear. Secondly, the motor we ordered was not arrived, hence we had to use a new motor, however, these two motors had different limited voltage, and if we wanted to use the motor we had, which the limited voltage is 3-6 voltage, then the old H-bridge (LMD 18200) was no longer adjust. As a result, we decided to change the chip. we use L293D motor driver instead Shown in Figure 1. it can provide bidirectional current 1A at the voltage 4.5V to 36V that will fit our motor.The L293D are quadruple high-current half-H drivers. These devices are designed to drive a wide array of inductive loads such as relays, solenoids, DC and bipolar stepping motors, as well as other high-current and high-voltage loads.

Figure 1

Figure 1 shows the pin functions of L293D motor driver.

Figure 2

Figure 3 shows the block functions of motor driver L293D.

We began to design a new circuit, as shown in Figure 3

Figure 3

 the new circuit contained four capacitors, which are used to control the direction of current flow through motor. Connect a encoder to detect the real time speed, however the diameter for the plate of the encoder is much larger than the bearing axle of the motor, thus we need to make a ring to over-striking the bearing axle so that it would fit the encoder plate. We also asked the technician for help to make a PCB, which used to connect encoder, shown in Figure 4.

Figure 4

 The testing result was positive, when connected to the power supply, the motor worked well.