1) Load Cell Circuit: Our load cell circuit uses a half
Wheatstone bridge, as shown in Figure 2 [1]. Specifically, it
has two fixed-value resistors (the two resistors on the lefthand
side of the bridge in the figure) and a three-wire load
cell (shown on the right-hand side of the bridge in the figure).
The voltage between the connection of two fixed resistors and
the ground is a fixed value with/ without stress. The threewire
load cell is made of two single strain gauges in series.
When the three-wire load cell is stressed, one of the strain
gauges is compressed and results in a decreased resistance,
and at the same time the other strain gauge is stretched and
leads to an increased resistance. Thus, the voltage between the
connection of these two strain gauges and the ground increases
as a response to the introduction of the external weight.
The output of the load cell circuit is thus the voltage
between these two connections, which is linear to the weight
value
Vin = V +
in
−V
−
in = (
R3
R3 − R4
− R2
R1 − R2
)∗(Vcc−Vss). (1)
In our system, we use Generic YZC-161B load cells with a
nominal load of 50 kg, as shown in Figure 3, which costs
around $.70 and is generally used as a weighing scale.