Laser detection and indicating device system circuit design

Laser is widely used in industry. In the past, its effect was often observed with the naked eye in the field of measurement and indication. The following introduces a device that can detect laser light (red light 650nm), and use indicator lights to alarm and indicate through relevant electronic circuits, thereby replacing the human eye and improving measurement and indication accuracy.

Laser and its circuit

This design requires a laser that is cost-effective and capable of emitting 650nm red light. Comprehensive considerations: semiconductor laser technology matures earlier and develops rapidly. It has a wide wavelength range, is simple to manufacture, has low cost, is small in size, light in weight, and has long life, so semiconductor lasers were selected. Since it was considered in the early stages of the design that this project would be applied to gear correction, a milliwatt-level one-line semiconductor laser was selected.

The operation of a semiconductor laser is closely related to the driving power supply. Many factors such as transient current or voltage spikes can easily damage the laser. A power detection circuit is designed, using Maxim's MAX810. The MAX810 is a single-function microprocessor reset chip used to monitor the supply voltage of microcontrollers and other logic systems. It can provide reset signals to the microcontroller during power-on, power-down, and power-saving conditions. When the power supply voltage is lower than the preset threshold voltage, the device will send out a reset signal until the power supply voltage returns to above the threshold voltage within a period of time. The MAX810 has a high-level active reset output. The threshold voltage of MAX810 is 2.63V, which is designed for 3V power supply. A reset signal is generated when the power supply voltage drops below the reset threshold. This reset signal will remain until the power supply voltage is above the threshold voltage for at least 140ms, and then the reset signal is released. This delay time helps ensure a valid reset signal when the supply voltage is unstable. The circuit is shown below.

Detection circuit

The detection circuit consists of two parts: sub-detection circuit and main detection circuit. Subcircuits are connected to the main circuit via striplines. Up to four subcircuits can be connected. The sub-detection circuit is mainly a photoelectric transistor circuit. When light shines on the base area of ​​the phototransistor, electron-hole pairs are generated. The electrons are swept into the collection area by the strong electric field inside the collection area with reverse bias, forming a larger collector current. At the same time, on the resistor connected in series with it, changes in pressure drop. The circuit is shown below.

The main detection circuit is composed of a signal detection circuit composed of 555 integrated circuit and a wireless transmitting circuit composed of SC2262. The signal detection circuit is shown in the figure below.

The power supply used in this part of the circuit is 9V, so when the input signal is less than 3V, the output is high level: when the input signal is greater than 6V, the output is low level. At the same time, it drives the transistor and sends the signal to the wireless transmitting circuit. In the figure, C1, Dl, and R1 form a reset circuit. At the moment when the power is turned on, capacitor C1 is equivalent to a short circuit, that is, pin 4 is low level. Regardless of pin 2 and paired use, there is a maximum of 12-bit three-state coding. The circuit has a power saving mode and can be used in applications such as radio and infrared remote control transmission. The transmitting module used in the design can send four bits of data to the receiving end.

Signal processing and indication circuit

This circuit consists of four parts: power supply, wireless reception, signal processing, and status indication. Since this part of the circuit uses a 5V power supply, a DC/DC converter is used to convert 3V into 5V. MAX641 is a step-up DC/DC converter produced by MAXIM Company in the United States. The power consumption of MAX641 is less than 135μA, while its conversion efficiency is as high as 80%. The circuit is shown below.

The circuit is composed of switching power tube V1, storage inductor L and freewheeling diode D7. The error comparator inside the chip works together with the internal oscillator to switch the N-channel power MOSFET on and off, allowing the inductor to store and release energy, so that the output voltage is fixed at 5V. At the same time, the circuit has a low voltage indication circuit. D8 lights up when the voltage is lower than the set value. The wireless receiving circuit is composed of SC2272 and its auxiliary circuits and receives four-bit data. The data is then sent to the signal processing circuit. Signal processing circuits are composed of digital logic circuits. Assume the four bits of data are A, B, C, and D respectively. Make the logic circuit complete a function. When one bit of data is valid, Y1 is high level; when two bits of data are valid, Y2 is high level; when three bits of data are valid, Y3 is high level; when four bits of data are valid, Y4 is high level. . This function can detect the number of valid digits of the phototransistor to determine the status of the object being measured.