Thank you for your reply sheepdog43.
I just stick 2 wound tapes above the sensor. Now I have changed to Johann's version. Fortunately I got good result in printing.
The following was my G29 result:
Bed x: -22.50 y: -67.50 z: -23.72 FSR: 718
Bed x: 0.00 y: -67.50 z: -23.63 FSR: 753
Bed x: 22.50 y: -67.50 z: -23.65 FSR: 686
Bed x: 45.00 y: -45.00 z: -23.67 FSR: 702
Bed x: 22.50 y: -45.00 z: -23.59 FSR: 706
Bed x: 0.00 y: -45.00 z: -23.60 FSR: 725
Bed x: -22.50 y: -45.00 z: -23.62 FSR: 730
Bed x: -45.00 y: -45.00 z: -23.64 FSR: 764
Bed x: -67.50 y: -22.50 z: -23.75 FSR: 731
Bed x: -45.00 y: -22.50 z: -23.67 FSR: 762
Bed x: -22.50 y: -22.50 z: -23.69 FSR: 671
Bed x: 0.00 y: -22.50 z: -23.61 FSR: 724
Bed x: 22.50 y: -22.50 z: -23.52 FSR: 761
Bed x: 45.00 y: -22.50 z: -23.64 FSR: 695
Bed x: 67.50 y: -22.50 z: -23.76 FSR: 696
Bed x: 67.50 y: 0.00 z: -23.67 FSR: 737
Bed x: 45.00 y: 0.00 z: -23.59 FSR: 726
Bed x: 22.50 y: 0.00 z: -23.61 FSR: 706
Bed x: 0.00 y: 0.00 z: -23.53 FSR: 746
Bed x: -22.50 y: 0.00 z: -23.64 FSR: 678
Bed x: -45.00 y: 0.00 z: -23.66 FSR: 726
Bed x: -67.50 y: 0.00 z: -23.78 FSR: 680
Bed x: -67.50 y: 22.50 z: -23.74 FSR: 749
Bed x: -45.00 y: 22.50 z: -23.76 FSR: 645
Bed x: -22.50 y: 22.50 z: -23.58 FSR: 798
Bed x: 0.00 y: 22.50 z: -23.60 FSR: 714
Bed x: 22.50 y: 22.50 z: -23.61 FSR: 683
Bed x: 45.00 y: 22.50 z: -23.53 FSR: 783
Bed x: 67.50 y: 22.50 z: -23.65 FSR: 718
Bed x: 45.00 y: 45.00 z: -23.56 FSR: 759
Bed x: 22.50 y: 45.00 z: -23.58 FSR: 731
Bed x: 0.00 y: 45.00 z: -23.70 FSR: 658
Bed x: -22.50 y: 45.00 z: -23.72 FSR: 685
Bed x: -45.00 y: 45.00 z: -23.73 FSR: 707
Bed x: -22.50 y: 67.50 z: -23.75 FSR: 701
Bed x: 0.00 y: 67.50 z: -23.67 FSR: 682
Bed x: 22.50 y: 67.50 z: -23.48 FSR: 770
-23.53 -23.65 -23.83 -23.81 -23.67 -23.72 -23.70 -23.74 -23.80
-23.72 -23.59 -23.63 -23.72 -23.63 -23.65 -23.67 -23.75 -23.86
-23.78 -23.70 -23.64 -23.62 -23.60 -23.59 -23.67 -23.75 -23.92
-23.84 -23.75 -23.67 -23.69 -23.61 -23.52 -23.64 -23.76 -23.87
-23.89 -23.78 -23.66 -23.64 -23.53 -23.61 -23.59 -23.67 -23.76
-23.73 -23.74 -23.76 -23.58 -23.60 -23.61 -23.53 -23.65 -23.76
-23.77 -23.75 -23.73 -23.72 -23.70 -23.58 -23.56 -23.55 -23.70
-23.81 -23.89 -23.83 -23.75 -23.67 -23.48 -23.57 -23.52 -23.56
-24.04 -24.03 -23.93 -23.78 -23.64 -23.39 -23.27 -23.48 -23.47
I increse the home distance to prevent the hotend dragging on the bed while G29.
I think the analog signal is better than digital signal for auto levelling.