Voice Control Toy Car

The principle circuit is shown in the attached figure. The electret microphone MIC converts the picked-up sound signal into an electrical signal, which is then amplified by VT1 and inverted by VT2. IC1 and IC2 are respectively controlled to drive the forward and backward motor M1 and the turning motor M2 (or turning electromagnet) to work. R1 and R2 are the bias resistors of MIC. They can change the receiving sensitivity, that is, the distance of the voice control. The high-frequency bypass capacitor C1 and the coupling capacitor C2 can select the frequency of the voice control command (such as whistle, clapping, etc.) within a certain range to reduce noise interference and increase the reliability of voice control. Ic1 and Ic2 use a bipolar single-time base circuit LM555 (or a dual-time base LM556), and its maximum drive current can reach more than 200mA. IC1 is connected in a monostable mode, and the transient time is generally calculated according to t=1·1RP·e3. IC2 is connected in a trigger mode, and M1 and M2 are connected between the output terminals of IC1 and IC2.

When MIC does not receive a valid voice control signal, VT1 is turned off, VT2 is turned on, IC2 makes pin 3 low because pin 2 is high, IC2 makes pin 3 output high because pin 2 and 6 are low, M1 gets positive current and rotates forward, and the toy car moves forward. At this time, because VD is reverse biased and cut off, the turning motor M2 has no current and does not work; when MIC receives a command signal with a certain frequency and sound intensity, VT1 is turned on, VT2 is turned off. Ic1 pin 2 is low, making its pin 3 high, IC2 makes its pin 3 low because pin 2 and 6 are high. M1 gets negative current and reverses, and the toy car moves backward. At the same time, VD is turned on, and M2 gets negative current (positive current is also acceptable) to make the toy car turn. After the transient time t, Ic1 pin 3 flips to low level, M1 gets positive current to make the toy car continue to move forward in the direction after turning, and at the same time, M2 loses current due to VD cutoff and stops turning.

It should be noted that if the transient time of IC1 is long (determined by RP), when the pin 3 of IC1 still outputs a high level, VT1 is cut off due to the disappearance of the voice control signal, VT2 is turned on, and the pin 3 of IC2 outputs a high level. Then both ends of M1 and M2 are high level. Therefore, both motors stop working, and the toy car will pause for a while (several hundred milliseconds to 1 second). After the transient time ends and the pin 3 of IC1 flips back to a low level, M1 will rotate forward and the toy car will continue to move forward. This instantaneous pause will not affect the operation of the toy car. Adjusting RP can eliminate the above pause phenomenon.