The four load cells form the sensor mechanism but to calculate the actual weight and subsequently display it is a job performed by a custom micro-controller and associated circuitry on the small printed circuit board found in the top left of the scale.
Unfortunately for me the technology has now evolved so that almost all the processing is done by a single custom chip located in the center of the PCB. This chip is covered by a black blob (chip-on-board) as a cost effective way to mount the circuit without expensive packaging. The net effect of this is that the internal workings of the circuit are effectively a black box to me. (I have no intention of dissolving the epoxy and getting my microscope out at this stage!). The PCB shows a number of interesting features: firstly there are several connectors arranged towards the edges of the board. On the left hand side we see 16 lines that go to the custom LCD panel via a flexible connector, at the top and right we have two connectors CON1 and CON2 and at the bottom we have connectors that go to the battery and the load sensors.
There are parts of the board that are not populated so we can conclude that this is a module that is used in different scales and the parts that are required are populated according to the requirements for the end product.
On the bottom side (actually the first side you see) of the PCB there are few components. Here we find mounted a push button switch which is used to cycle the scale between kg, lb and st/lb unit of measurement.