Hi friends!,
This morning i set new prototype, following the instructions, on article: Bridge Circuits, USING A SINGLE OP AMP AS A BRIDGE AMPLIFIER FOR A SINGLE-ELEMENT VARYING BRIDGE.
". The key redeeming feature of the circuit is that it is capable of single supply operation and requires a single op amp.
Note that the RF resistor connected to the non-inverting input is returned to VS/2
(rather than ground) so that both positive and negative values of DR can be
accommodated, and the op amp output is referenced to VS/2."
Now i got better results !!!, at last the Vo is not satured.
To get a gain (Vo/Vi) about 100x, i use 1K(considering 500R from load cell) and 150k resistor.
Placed a 1uf poliester capacitor on OPA power source, and 100nf capacitor on SIG+ and SIG-.
Tested Schematic:
**broken link removed**
New board with much less wires:
**broken link removed**
Test results from OPA Vo (in volts):
CI_________No Load____2Kg________10Kg_______Diference 0-10Kg
OP07_______2.61_______2,94_______4,94 _______1,63
TL081______1,509______1,512______1,533______0,024
LM301______3,43_______3,68_______4,52_______1,09
LM318______2,34*______2,67_______3,56_______1,22
UA741______2,19_______2,51_______3,81 _______1,62
* this case is very strange, if i aproximate my hand of CI, the voltage variables from 2,34 to 2,64. Just aproximate at 1 or 2 centimeters.
Now i must understand why the Gain is not linear. But so was told to me, the single op amp configuration has poor gain accuracy.
Thank´s
Daniel