Electronic balance

EE December 1986 by R Ochs 34 ELECTRONIC BALANCE This accurately operating balance, which is entirely composed of electronic parts, features a 31/2 digit read-out, a tare offset facility, and a weighing capacity of 500 grammes. Based upon the use of a common bass loudspeaker as the weight sensor, this novel household utensil is readily built and extremely useful for a variety of hobby applications, and, of course, for cooking! Like most types of electronic balance, the proposed low-cost ver- sion is based on the underlying prin- ciple of electromagnetic force compensation. Since the force on a conductor placed in a magnetic field is proportional to the coil current causing the field, the voice coil in a loudspeaker can be used as a force sensor, if weight is transferred direct onto the cone and thus onto the voice coil. After measuring the cone displacement, an electronic control circuit arranges for a current to be sent through the voice coil, causing the initial position of the ...