Abstract: A variable resistance measuring loop having compensation function for environmental factor is disclosed. The measuring loop comprises a central processing unit CPU connected by one end of the variable resistance to the PO.1 leg thereof, and the other end being connected to the PO.2 leg thereof, the center end thereof being connected to a drain of a charging switch transistor Q, the base of the transistor Q being connected in series with a resistance R to the PO.3 leg of the CPU, the emitter of the transistor Q being connected to VDD power source end, the drain being conductive with the PO.

Abstract: A method for forming a keyboard switching circuit without generating phantom phenomenon is disclosed. The method includes the steps of (1) forming a matrix of nodes with input/output terminals of the keyboard circuit; (2) selecting nodes from the matrix to define a reference diagonal line which divides the matrix into upper and lower portions; (3) selectively selecting nodes of the matrix in the upper and/or lower portions to define diagonal lines parallel to the reference line, the diagonal lines being located at different distance from the reference lines and the nodes of the diagonal lines forming no rectangle with each other; and (4) setting switches in the selected nodes. Since no rectangle can be formed among the switches, no reverse current may be caused by simultaneous actuation of three switches of a rectangle and thus effectively eliminating phantom phenomenon.