Operational Amplifiers I

A lot of time, we will encounter the situation when that a signal (voltage) that is sent by the sensor is too small/big that we cannot just directly send the signal into the micro-controller(processor). Thus, we need a device to condition the signal. The device we use is call operational amplifiers or Op amps.

the packages it uses have eight legs

In this experiment, we assume that we have a sensor which has an output ranges from 0 to 1V with negligible impedance. The specification for the Signal conditioning needs to be 0 to -10v
and must draw no more than 1mA from the sensor and the op-amp supplies should supply no more than 30mW of power each.

here is the schematic of the circuit

 first, we need to determine the value of R1
since the max input voltage is 1 and we want it be lower than 1mA
we can determine the value R1 =(1V)/1mA  =  1kΩ

next, we need to determine the feedback resistor
since the max output voltage is 10
10V=Rf/1000
Rf=10KΩ

Next we need to determine Rx
since Rx is to be 1/4W resistor and we want to operate at half of its rated power
The worst case voltage across Rx occurs when Ry is set to zero
(1/8)W=(6^2)/Rx
Rx=1152Ω

Determine Ry
Assuming the value of Rx  determined above and no loading on the divider
Ry that will yield 1V across it
1=[Ry/(288+Ry)]6

Ry=57.6Ω

The Thevenin equivalent of the divider circuit from the inverting amplifier
Rth=48Ω

and the thevenin resistance is at least a factor of 20 times smaller than the resistance value for Ri

Next, we devise the experiment

we record the values of the components

Component	Nominal Value	Measured Value	Power or Current Rating
Ri	1K Ω	984Ω	1/4W
Rf	10k Ω	9.9KΩ	1/4W
Rx	288 Ω	287Ω	1/4W
Ry	57.6 Ω	58.8Ω	1/4W
V1	12V	12.13V	12W
V2	12V	12.06V	12W

Next we build the circuit on the breadboard

 



 Next we record the data from the output by looking at the multimeters we set up for the experiments

Vin (V)	Vout(Measured)(V)	GAIN(Calculated)	V_Ri(mA)	I_Ri(Calculatd)(mA)	V_Rf(Measrued)(V)
0	-0.05	0	-0.007	-0.007113821	0.06
0.25	-2.54	-10.16	0.269	0.273373984	2.57
0.5	-5.08	-10.16	0.536	0.544715447	5.12
0.75	-7.56	-10.08	0.797	0.80995935	7.62
1	-9.91	-9.91	0.946	0.961382114	9.91

Power supply current
Iv1=2.32mA
Iv2=1.49mA

P_V1=12.13*2.32mA=28.14mW
P_V=12.06*1.49mA=17.97mW
Both power supply are less than 30 mW.