###### Abstract  
The frequency stability of free-running lasers is susceptible to the influence of environmental factors, which cannot meet the long-term frequency stabilization requirements for atom interferometry precision measurements. To obtain a frequency-stabilized 780 nm laser beam, an automatic frequency stabilization system for an external cavity diode laser (ECDL) based on rubidium (Rb) atomic saturated absorption spectrum was designed using a commercial data acquisition (DAQ) card. The signals acquired by the A/D terminal are processed and analyzed by LabVIEW, which can automatically identify all the locking points and output the piezoelectric ceramic transducer (PZT) scan and digital feedback through the D/A terminal. The experimental results show that the system can lock to six different frequencies separately and realize automatic relocking within 3.5 s after unlocking. The system has a stability of 1.68 \(\times\) 10\({}^{-10}\)@1 s and 4.77 \(\times\) 10\({}^{-12}\)@1000 s, which meets the laboratory's requirements for atomic interference experiments.  
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Footnote †: journal: Applied sciences  
(Digilock 110) with a frequency stability of 1.2 \(\times\) 10\({}^{-12}\)@30 s [14]. The commercial server has the advantages of high precision and good performance, but it also faces the problems of high cost, large size, and difficult maintenance. [PERSON] et al. used a commercial wavemeter to achieve laser frequency stabilization, and an absolute Allan deviation below 10\({}^{-9}\) over 10 h was achieved [15]. A wavemeter can only be locked in a specific wavelength range, and a high-precision wavemeter is more expensive. [PERSON] et al. designed an automatic frequency stabilization system based on microcontroller unit (MCU) digital assistance with a frequency stability of 8.39 \(\times\) 10\({}^{-11}\)@1 s and 7.99 \(\times\) 10\({}^{-12}\)@1024 s [16]. MCU is limited by its performance and cannot implement complex digital algorithms. [PERSON] et al. designed a digital frequency stabilization system based on a field programmable gate array (FPGA) and long-term frequency stability up to 10\({}^{-11}\)[17]. [PERSON] et al. created an automatic frequency stabilization system based on digital signal processing (DSP) technology [18]. The above digital control is written in code, is easy to modify, and can save cost to a certain extent, but providing a convenient observation interface is challenging. [PERSON] designed an automatic frequency stabilization system based on MTS by controlling FPGA through LabVIEW programming with frequency stability up to 1.3 \(\times\) 10\({}^{-9}\)@1 s and 3 \(\times\) 10\({}^{-11}\)@2000 s [19], but the threshold could only be judged once, and multiple absorption lines could not be selected and locked. [PERSON] et al. adopted the frequency stabilization system of a computer with a DAQ card to realize automatic locking to the center of any selected gas absorption line [20]. Still, they could not realize relocking after the system lost lock.  
This work used an NI commercial DAQ card (USB-6211) to construct a laser automatic frequency stabilization system with a friendly interactive interface for 780 nm ECDLs. PZT scanning was performed at the D/A terminal of the DAQ card driven by the computer, and the SAS was synchronously acquired at the A/D terminal. LabVIEW differentiates the SAS signal to obtain the error signal, smooth filtering, incremental PI feedback control, rescanning, etc. The laser automatic frequency stabilization system based on the DAQ card can identify all spectral lines for locking and quickly rescan and lock again after the laser is unlocked. It provides a simple, practical, and low-cost automatic frequency stabilization strategy for the laser.