Study Of Dual-wavelength Laser Treatment Instrument Control System Based On RTOS For ATmega

In this topic, a practical laser control system is designed for 660nm and 808nm dual-wavelength semiconductor laser, which is used in medicine. It mainly includes two parts: a constant-current source circuit and a temperature conrtol circuit. The former can provide the adjustable constant drive current with maximal value of 2.5A for the medical laser, the latter uses thermoelectric cooler technique which is called TEC for short by us to control the temperature of the 660nm wavelength laser. The detailed points are as follows:a. The laser current source is mainly designed by the chip LT1006, which is the single supply power operational amplifier produced by Linear Technology Corporation. The circuit can supply output-current up to 2.5A by proggramming input of LT1006, NPN epitaxial silicon darlington transistor TIP142 and a 0.1Ωprecision resistance, providing high power driver for the laser. Meanwhile, it contains more than one feedback, make sure the stability of output-current. It also has a enabled control end, to shut down the constant-current source in order to protect the expensive laser when an exception occurred in the circuit.b. The temperature conrtol circuit of 660nm wavelength laser is a closed-loop feedback system consisting of a thermoelectric cooler(TEC), a negative temperature coefficient(NTC) and a instrumentation amplifier. NEC detects the temperature of the laser, then it is converted to voltage value and sent to instrumentation amplifier LTC2053. Meanwhile, the corresponding voltage value which stands for preset temperature is also given to LTC2053. After differential amplification of the two values, the output of LTC2053 is sent to thermoelectric cooler controller LTC 1923 produced by Linear Technology Corporation. The LTC1923 drives a full-bridge switching circuit which consists of two pairs of N-/P-channel MOSFETs Si9801. All in words,the described structure above can control the voltage size, current dirention and size of TEC, which may affect TEC operational states whether cooling or not and the rate. So, the system makes the laser working at a suitable temperature.c. The control part adopts the RTOS(Real-Time Operating System) kernel and platfom. The control chip is ATmega64L of AVR series microcontroller produced by ATMEL. After transplanting Small RTOS to ATemagaL, it can overcome the ATemagal’s shortcomings, such as limited internal resources, poor real-time, poor addressablility, slow operating speed and so on. Based on this, software development is designed to make the laser control system more intelligent. it mainly accomplish the human-machine interface operation, the control command communiication between control chip and other chips and to monitor and display the working state.The results show that the laser control system described in this paper can run very well. The software code is small in quantity, simple but efficient, easy to debug and modfify. So it has some theoretical and practical value.