Laser detection indicating device system circuit design

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Lasers are widely used in industry. In the past, in the field of measurement and indication, the effects were often observed by the naked eye. The following describes a device that can detect laser light (red light 650 nm) and replace the human eye with an indicator light alarm and indication through the relevant electronic circuit to improve measurement and indication accuracy.

Laser and its circuit

The design requirements for the laser are high cost performance and can emit red light at 650 nm. Considering comprehensively: semiconductor laser technology matures early and develops rapidly. Its wavelength range is wide, its fabrication is simple, its cost is low, and its size is small, its quality is light, and its life is long. Therefore, semiconductor lasers are selected. Since the project was originally applied to gear correction in the early stage of design, a milliwatt-level word line semiconductor laser was selected.

The operation of a semiconductor laser has a lot to do with the driving power supply, and many factors such as transient current or voltage spikes can easily damage the laser. A power-supply detection circuit was designed that utilized Maxim's MAX810. The MAX810 is a single-function microprocessor reset chip that monitors the supply voltage of microcontrollers and other logic systems. It provides a reset signal to the microcontroller during power-up, power-down, and power-saving conditions. When the supply voltage is lower than the preset threshold voltage, the device will issue a reset signal until the supply voltage returns to above the threshold voltage for a period of time. The MAX810 has an active-high reset output. The MAX810's threshold voltage is 2.63V, which is designed for 3V power supplies. A reset signal is generated when the supply voltage drops below the reset threshold. This reset signal is held until the supply voltage is above the threshold voltage for at least 140ms, after which the reset signal is released. This delay time helps to ensure a valid reset signal in the event of a power supply voltage instability. The circuit is shown below.

Detection circuit

The detection circuit consists of two parts: a sub-detection circuit and a main detection circuit. The subcircuit is connected to the main circuit through a strip line. Up to four subcircuits can be connected. The sub-detection circuit is mainly a phototransistor circuit. When the light is in the base region of the phototransistor, electron-hole pairs are generated, and the electrons are swept into the collection region by a strong electric field inside the collection region with reverse bias, forming a large collector current while being in series with the resistor. A change in pressure drop is formed. The circuit is shown below.

The main detection circuit is composed of a signal detection circuit composed of 555 integrated circuits and a wireless transmission circuit composed of SC2262. The signal detection circuit is shown 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: when the input signal is greater than 6V, it outputs low level. The transistor is driven simultaneously and the signal is sent 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, the capacitor C1 is equivalent to a short circuit, that is, the fourth pin is at a low level, and there is a maximum of 12 three-state codes regardless of the 2 pin and pairing. The circuit has a power saving mode and can be used for 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 indicating circuit

The circuit comprises four parts: power supply, wireless reception, signal processing and status indication. Since this part of the circuit uses a 5V power supply, it is applied to a DC/DC converter to change 3V to 5V. The MAX641 is a step-up DC/DC converter from MAXIM, USA. The MAX641 consumes less than 135μA, while converting 80%. The circuit is shown below.

The circuit consists of a switching power transistor V1, a storage inductor L and a freewheeling diode D7. The internal comparator's error comparator works in conjunction with the internal oscillator to turn the N-channel power MOSFET on and off, allowing the inductor to store energy and fix the output voltage to 5V. At the same time, the circuit has a low voltage indicating circuit. D8 illuminates when the voltage is lower than the set value. The wireless receiving circuit is composed of SC2272 and its auxiliary circuits and receives four bits of data. The data is then passed to the signal processing circuit. The signal processing circuit is composed of digital logic circuits. Let the four-digit data be A, B, C, D. Make the logic circuit complete a function, Y1 high level when one bit data is valid; Y2 high level when two bits of data are valid; Y3 high level when three bits of data are valid; Y4 high level when four bits of data are valid . This function detects the number of bits effective for the phototransistor to determine the state of the measured object.