The purpose of this design is to construct an Accelerometer Interface Circuit which
displays the acceleration measurement of an automobile and to indicate if the acceleration
or deceleration is exceeding the limit values. In addition, the designed circuit should also
signal to the automobile air bag deployment if acceleration or deceleration exceeds
certain specific limit value.
As a sensor for acceleration or deceleration of an automobile, the Model 1210 Analog
Accelerometer by Silicon Designs, Inc is supposed to be used for this design. However,
during the lab, a simulation circuit which resembles the Model 1210 Analog
Accelerometer is constructed instead of using the real accelerometer. Op-amps are used
in the simulation circuit to provide the same output as the Model 1210 Analog
Accelerometer. The output from Accelerometer Simulating Circuit is then sent to the
Accelerometer Interface Circuit.
The Accelerometer Interface Circuit includes op-amps circuits which adjust or change the
output voltage signal from the Model 1210 Accelerometer Simulator Circuit to the
desired output values and then send those adjusted signals to Indicator and Display
Circuits. To indicate or signal whether the acceleration or deceleration is exceeding the
limit, op-amps are used as comparators together with LEDs in the Display and Indicator
Circuit design. LEDs will display or signal when the acceleration or deceleration is
exceeding the limit. The generalized block diagram for Accelerometer Interface Circuit
is shown below.
Fig.1: Block Diagram Representation of Accelerometer and Indicator/Monitor Circuits
The Model 1210 Analog Accelerometer has two output pins, AOP and AON. One of the
outputs is chosen to send signals to Signal Conditioning Circuitry. Full scale acceleration
range of accelerometer is 10G. The voltage from AOP or AON varies with respect to
acceleration linearly. When the deceleration is –10G, which is full scale, AOP and AON
gives the output voltage 0.5 and 4.5 respectively. For the full scale 10G, AOP and AON
gives 4.5 and 0.5 respectively. When there is no acceleration, which is 0G, both pins
give output voltage of 2.5V. (Note: 1G = 9.8 m/s)
The plot of output voltage from AOP or AON pin from the Model 1210 Analog
Accelerometer verses acceleration in full scale range is shown below.
Fig.2: AON and AOP outputs from Model 1210 Accelerometer
The Accelerometer Simulating Circuit which resembles the Model 1210 Analog
Accelerometer is constructed to provide one of the outputs (AOP or AON) the same as
those of real accelerometer. In this design, the simulator circuit is constructed in such a
way that it resembles and provides AON output signal to Signal Conditioning Circuitry.
1 kHz, 10V(p-p) peak to peak triangle wave from waveform generator is used as an input
to simulating circuit to mimic the acceleration or deceleration signals.
The Signal Conditioning Circuitry received an input signal from Accelerometer
Simulating Circuit and gives two output signals, one for Air Bag Deployment Indicator
Circuit and another one for Acceleration or Deceleration Indicator Circuit. One of the
output signals gives –5V to 5V, which is linearly corresponding to –10G to 10G.
Another output signal provides 0V to 5V, which linearly corresponds to –0.2G to 0.2G.
The output signal which gives –5V to 5V is send to Air Bag Deployment Indicator
Circuit which signals to air bag deployment when acceleration or deceleration exceeds
0.6G. Another output signal is send to Acceleration or Deceleration Indicator Circuit
which indicates that acceleration or deceleration is changing too rapidly. In this design,
the value of 0.1G is chosen as a limit and the circuit is constructed in a manner to indicate
that acceleration or deceleration is high if it exceeds 0.1G. Op-amps are used in this
design as linear and non-linear components (comparators). The detailed block diagram
for this design is shown in Fig. 3.
Fig. 3: Detailed Block Diagram of Accelerometer Interface Circuit
Circuit Design and Supporting Analysis
Accelerometer Simulating Circuit
LF 412 Op-amp is used as an inverting summer to receive the output voltage
range from 0.5V to 4.5V. One of the input signals to inverting terminal is 1 kHz, 10Vp-p
triangular wave from waveform generator, which mimics the acceleration or deceleration
signal to accelerometer, and the other input is –15V DC. The non-inverting terminal is
The following is the design and circuit analysis of Accelerometer Simulating
Circuit. The circuit is constructed in a manner to give output, which resembles AON
output of Model 1210 Analog Accelerometer.
–10V corresponds to 4.5V output.
10V corresponds to 0.5V output.
0 . 5 4 .5
VOUT ( 4.5) VIN ( 10 )
10 ( 10 )
VOUT 0.2V IN 2.5
Therefore, the close loop gains are –0.2V/V and –0.167V/V for triangular wave
input and –15V DC input respectively.
VOUT 0.2VIN 0.167V
VOUT VIN 2 V
R1, R2 and R3 are chosen 50k, 10k and 60k respectively to get the desired
close loop gains. V– is chosen to be –15V DC.
Fig. 4 shows the schematic diagram for Accelerometer Simulating Circuit.
Fig. 4: Accelerator Simulating Circuit
Signal Conditioning Circuitry
Since Signal Conditioning Circuitry receives input signal from Accelerometer
Simulating Circuit, the input signal ranges from 0.5V to 4.5V. The Signal Conditioning
Circuit includes two portions. Each portion provides two different output signals, one for
Air Bag Deployment Indicator Circuit and another one for Acceleration or Deceleration
Indicator Circuit. One output ranges from –5V to 5V which linearly corresponds to
–10G and 10G. The other output ranges from 0V to 5V linearly corresponding from
–0.2G from 0.2G.
–10G (–10V) gives 4.50V which corresponds to –5.0V output
10G (+10V) gives 0.50V which corresponds to +5.0V output
5.0 ( 5.0)
VO1 ( 5.0) VOUT 4.5)
0.5 ( 4.5)
VO1 2.5VOUT 6.25
Therefore, the close loop gains are –2.5V/V and –0.417V/V for input signal from
VOUT and –15V DC input respectively.
VO1 2.5VOUT 0.417V
VO1 VOUT 4 V
R4, R5 and R6 are chosen 10k, 4k and 24k respectively.
V– is chosen to be –15V.
Fig. 5 shows the schematic diagram of Signal Conditioning Circuitry which gives
VO1 linearly corresponds to –10G to +10G.
Fig. 5: Signal Conditioning Circuit, Part I
From Accelerometer Simulating Circuit, the equation, VOUT 0.2VIN 2.5 gives
voltage ranges from 2.54V to 2.46V, linearly corresponding from –0.2G to +0.2G
–0.2G (–0.2V) gives 2.54V which corresponds to 0V output (VO2)
0.2G (+0.2V) gives 2.46V which corresponds to 5V output (VO2)
VO 2 (0.0) VOUT 2.54
2.46 ( 2.54 )
VO 2 62 .5VOUT 158 .75
Therefore, the close loop gains are –62.5V/V and –10.58V/V for input signal
from VOUT and –15V DC input respectively.
VO 2 62.5VOUT 10.58V
VO 2 VOUT 7 V
R7, R8 and R9 are chosen 100k, 1.6k and 10k respectively.
V– is chosen to be –15V.
Fig. 6 shows the Signal Conditioning Circuitry which gives VO2.
Fig. 6: Signal Conditioning Circuit, Part II
Display for Acceleration Measurements
This circuit receives input signal from Part II of Signal Conditioning Circuitry,
which is VO2. LF 412 op-amps are used as comparators to indicate whether the
acceleration or deceleration exceeds 0.1G (+0.1V). If the acceleration or deceleration
exceeds, the circuit LED will be turned on.
–0.1V gives 2.52V which corresponds to 1.25V VO2
0.1V gives 2.48V which corresponds to 3.75V VO2
Therefore, VC for two comparators must be 1.25V and 3.75V each.
VC = 1.25V is chosen for inverting comparator since deceleration exceeds –0.1G
VO2 will give voltage value lower than 1.25V and the inverting comparator will
give high voltage value when VO2 is less than VC, which is 1.25V, and the LED
will be turned on when it is forwardly biased.
VC = 3.75V is chosen for non-inverting comparator since acceleration exceeds
+0.1G, VO2 will give voltage value higher than 3.75V and the non-inverting
comparator will give high voltage value when VO2 is greater than VC, which is
3.75V, and the LED will be turned on.
To get two VC values, +15V is supplied to two voltage divider circuits
respectively and the outputs of two voltage divider circuits are connected to
The analysis for voltage divider circuits connected to inverting comparator:
1.25V (15V )
Therefore, R10 and R11 are chosen for 1k and 11k respectively.
The analysis for Voltage Divider Circuit connected to non-inverting comparator:
3.75V (15V )
Therefore, R12 and R13 are chosen for 10k and 30k respectively.
From the circuit analysis of two comparators, V'O2-1 will be high voltage when
VO2 is lower than 1.25V. Similarly, V'O2-2 will be high voltage when VO2 is
greater than 3.75V. Between these values, the voltage will be low.
The two outputs from two comparators (V'O2-1 and V'O2-2) are sent to inverting
summer and the two signals are then superimposed. Then the output from
inverting summer is sent to another op-amp which inverts the signal and added
+7.5V DC offset. The output (V"O2) is then connected to LED to display the
acceleration measurements. The two close loop gains for inverting summer is
Analysis is as follows:
R19 R16 ' R16 ' R19
R VO 2 1 R VO 2 2 R V
R20 17 18 21
1 ' 1 ' 1
VO 2 1 VO 2 1 VO 2 2 V
3 3 2
Therefore, R16, R17, R18, R19, R20, and R21 are chosen 10k, 30k, 30k, 10k,
10k, and 20k respectively.
Fig. 7 shows the schematic diagram of Acceleration or Deceleration Indicator
Fig. 7: Acceleration or Deceleration Indicator Circuit (LED circuit are omitted)
Acceleration Monitor for Air Bag Deployment
This circuit receives input signal from Part I of Signal Conditioning Circuitry. LF
412 Op-amps is again also used as a comparator to indicate whether the acceleration or
deceleration exceeds 6G (6.0V). If the acceleration or deceleration exceeds, the LED will
be turned on.
6G (6.0V) gives 1.3V which corresponds to 3.00V VO1
Therefore, VC for the comparator must be 3.00V
Non-inverting comparator is chosen since acceleration exceeds 6G, VO1 will give
voltage value greater than 3.00V and the non-inverting comparator will give high
voltage value when VO1 is greater than VC, which is 3.00V. Then LED will be
The analysis for voltage divider circuit connected to the comparator is as follows:
3.00V (15V )
Therefore, R14 and R15 are chosen for 10k and 30k respectively.
Fig. 8 shows the schematic diagram of Air Bag Deployment Indicator Circuit.
Fig. 8: Air Bag Deployment Indicator Circuit (LED circuit is omitted)
V'O1 will give high voltage value when VO1 is greater than VC and LED will be
Data and Measurements
Measurements and plots for Accelerometer Simulating Circuit are as follows:
XY plot of VIN Vs. VOUT on the HP oscilloscope is shown in Fig. 9 and 10.
VIN = -10V corresponds to VOUT = 4.5 V
VIN = +10V corresponds to VOUT = 0.4375V
Fig. 9: VIN Vs. VOUT plot on HP oscilloscope showing VOUT range
Fig. 10: VIN Vs. VOUT plot on HP oscilloscope showing VIN range
Measurements and plots for Signal Conditioning Circuitry Part I are as follows:
XY plot of VIN Vs. VO1 are shown in Fig. 11 and 12.
VIN = –9.875V corresponds to V1 = –5.0 V
VIN = +10.120V corresponds to VOUT = 5.0V
Fig. 11: VIN Vs. VO1 plot on HP oscilloscope showing VO1 range.
Fig. 12: VIN Vs. VO1 plot on HP oscilloscope showing VIN range.
Measurements and plots for comparator output of Air Bag Deployment Indicator
Circuit are as follows:
In Fig. 13, square wave represents output of Air Bag Deployment Indicator
Fig. 13: VIN and V'O1 plot on HP oscilloscope (square wave represent V'O1)
In Fig. 14, the comparator output sharply changes from low voltage to high
voltage when the acceleration is 5.750G.
Fig. 14: VIN Vs. V'O1 plot on HP oscilloscope showing that V'O1 gives high voltage value
when VIN is greater than 5.75G
Measurements and plots for Acceleration or Deceleration Indicator Circuit are as
XY plot of VIN Vs. VO2 on the HP oscilloscope is shown in Fig. 15 and 16.
VIN = 0.2V corresponds to VO2 = 0.0 V
VIN = +0.2V corresponds to VOUT = 5.0V
Fig. 15: Plot of VIN and VO2 showing VO2 range.
Fig. 16: Plot of VIN and VO2 showing VIN range (0.1V to 0.1V).
In Fig. 17 and 18, XY plot of VIN Vs. each comparator output is shown.
Fig. 17 shows that comparator output changes from high voltage to low voltage
value when deceleration is less than 0.1G.
Fig. 17: Plot of VIN and V'O2-1.
Fig. 18 shows that comparator output changes from low voltage to high voltage
when acceleration is greater than 0.15G.
Fig. 18: Plot of VIN and V'O2-1.
According to V"O2 from Fig. 19, LED will be turned on when the voltage is high,
and turned off when the voltage is low.
Fig. 19: Plot of V"O2.
The PSpice Simulation diagram and Measurements for VIN, VOUT, VO1, VO2,
V'O2-1, V'O2-2, and V"O2 are attached in Appendix A, B, C, and D for references.
There are some discrepancies between theoretical values and experimental values.
Since the exact values of resistors cannot be obtained and the resistors values have error
percentage, small amount of experimental error percentages are expected in the design.
Another reason for having error percentage is that since some voltages such as VO2, and
V"O2 from Acceleration or Deceleration Indicator Circuit are in a very small range and
the lab room also has some noises, the exact analytical values cannot be obtained.
Some of the error percentages, which are noticeable and significant, are shown
Experimental value of VOUT which corresponds to 10G is 0.4375V.
Analytical value is 0.5 V.
Error Percentage = 100 12 .5%
Experimental value of Acceleration for Air Bag Deployment Circuit is 5.75G.
Expected value is 6G.
Error Percentage = 100 4.17 %
Experimental value of acceleration which triggers high voltage output from one of
the comparator circuit is 0.15G.
Expected value is 0.1G.
Error Percentage= 100 50 %
This error percentage is very large and undesirable. However, since the values
are so small that the exact measurement cannot be obtained from the available
oscilloscope. Although volt per division is adjusted on the oscilloscope display,
the exact value is still difficult to measure.
In this lab experiment, Op-amp's linear and non linear behaviors are observed.
The cascading effect of op-amps is also learned in this design project. Op-amps can be
used in linear circuit to amplify signals as well as in non linear circuit as a comparator.
As in a linear circuit, Op-amps can be used to invert a signal, sum up multi input signals,
or amplify or reduce a signal. The close loop gain can be obtained by varying feed back
resistors values. Using as an inverting op-amp in the design is easier to get desired close
loop gain by varying the resistor values. In addition, op-amps are also used to reduce the
input voltage signal by adjusting the close loop gain less than 1. If AC and DC sources
are supplied to an op-amp, the amplified or reduced DC output voltage will become the
offset of AC output voltage. Comparators are useful in converting an arbitrary waveform
into rectangular waveform. As in a non-linear circuit, op-amps are used as a comparator
to determine that the input voltage is above or less than threshold voltage. A comparator
op-amp gives two output signals, high voltage and low voltage, depending on whether the
input signal is higher or lower than the threshold voltage. Circuit designer can choose
any one of two types of comparators, inverting and non-inverting, based on the design
requirement. Such kind of behavior of op-amps can be used in the implementation of
designs such as temperature control systems and the acceleration or deceleration indicator
we have learned in this lab.