Triangle Signal Generator

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QUEENSLAND UNIVERSITY OF TECHNOLOGY

Electronics Report

Electrical and Computer Engineering ENB205

Aaron Palm David Lane Jay Sampson

11/4/2011


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ContentsSchematic ...................................................................................................................................................... 2

Components .................................................................................................................................................. 2

Calculations ................................................................................................................................................... 4

Schmitt Trigger (Comparator) ................................................................................................................... 4

Integrator .................................................................................................................................................. 4

Difference Amplifier .................................................................................................................................. 5

Testing ........................................................................................................................................................... 6

Procedure .................................................................................................................................................. 6

Power Supply Setup .............................................................................................................................. 6

Test One ................................................................................................................................................ 6

Test Two ................................................................................................................................................ 6

Discussion.................................................................................................................................................. 7

Application .................................................................................................................................................... 9

Reference List .............................................................................................................................................. 10


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Schematic

Components

A triangle wave generator utilises both an integrating op-amp circuit and an external hysteresis

comparator also known as a Schmitt trigger. The Schmitt trigger works by utilising two threshold

voltages, an upper and a lower threshold, each being of equal magnitude. Once the input voltage

reaches either one of the thresholds the Schmitt trigger retains the voltage at that magnitude until thesignal reaches the opposing threshold and in turn switches the output polarity depending on which

threshold it remains. For example if the higher (+) threshold is reached the output will be positive until

the lower (-) threshold is reached and this will in turn switch the output to negative, thus producing a

square wave.

Schmitt Trigger Integrator Difference Amplifier

(Comparator)

Figure 1 [1]


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Utilising such a comparator allows the limits of the triangle wave output from the integrating circuit to

be controlled. Furthermore, an integrating circuit theoretically integrates the square or constant output

from the Schmitt trigger and results in a linear waveform.

This linear waveform is generated by the charging and discharging of the capacitor and by varying the

values of the capacitor and resistor (one at a time as they are in series) the frequency of the wave can

then be adjusted, increasing the capacitance increases the frequency as the charging and discharging

action will take longer.

The final component of the circuit is the difference amplifying circuit. The purpose of a difference

amplifying circuit is to amplify the difference between two signals. The triangle wave output is fed

through a voltage divider and which splits the voltage in between the output of the op-amp and the

inverting input of the op-amp. Additionally the voltage gain can then be altered by adjusting the ratio

between the two resistors in the voltage divider. The position of the wave can also be shifted either up

or down through the use of another voltage divider. The magnitude of the shift is set by utilising

another voltage divider which splits the voltage to ground and to the non-inverting pin of the op-amp.

Furthermore, the voltage V2 as seen on the schematic being fed into the non-inverting pin of the op-amp

is the magnitude of the shift.

Figure 2


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Calculations

Schmitt Trigger (Comparator)

Although the input of +15 V and -15 V was utilised, the operational amplifiers needs voltage to run.

Utilising the voltage divider equation,

( )

Integrator

Integrates and inverts square waveform

Using Kirchhoffs current law,

The circuit configuration with a resistor and capacitor coupled in series integrates and inverts the inputsignal.

The slope of the integrated output is,

Using the equation from earlier,

RC can therefore be found


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The 31.6 k value was achieved by using a potentiometer.

Difference Amplifier

Amplifies the difference between the two inputs utilising voltage dividers and the gain is controlled by

the ratio.

Since the gain depletes to a and therefore a 1V shift is needed to get above the x-axis

The respective voltages can now be defined.

The 52 k resistor was then split into a 47 k & a 10 k potentiometer to get exact values.


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Testing

Procedure

Power Supply Setup

1. Set DC output to tracking2. Link the positive from output one to negative of output two (This will invert the output from

the negative of output one)

3. Piggyback a common ground lead to the output 2 negative4. Plug non-inverting from output two into digital multimeter5. Plug common ground into the multimeters ground output6. Adjust voltage to +15V7. Replace the positive output with the inverting output and check to see if the multimeter is

reading close to -15V

8. Turn off multimeter and plug the non-inverting output, common ground and inverting inputinto the respective points on the breadboard

Test One

1. Output of the Schmitt trigger to channel one positive (orange wire)2. Output of the Triangle-signal generator to channel two positive (red wire)3. Ground out both channel negatives4. Adjust the oscilloscope so all scales are the same and the positions are zeroed

Test Two

1. Replace the output of the Schmitt trigger with the output of the difference amplifier (yellowwire)

2. Adjust the oscilloscope so all scales are the same and the positions are zeroed


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Discussion

Although the circuit components were calculated theoretically in respect to specific outputs, and applied

to practice in reality the outputs would not match up exactly and can be seen in the following tables and

figures.

Test One

Test Two

Figure 3

Figure 4


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There are several explanations for the discrepancies between the theoretical and experimental results

and some can be altered to give the desired outputs. Initially the voltage inputs were not exactly +15 V

and -15V and were +15.006 V and -14.966 V this therefore had a significant effect on the outputs.

Furthermore, the average saturation voltage of 12.5 V was assumed and is not exact therefore some

resistor values may have been off by 1 K. Furthermore, potentiometers were used to dampen thiserror as well as account for resistor values that could not be met by using pre-fabricated resistors with

set values. Additionally this can be seen in figure 5 and the schematic, and by carefully adjusting the

resistance to within a tolerance of1 K the correct frequencies, voltages and shifts could be achieved.Furthermore, the triangle wave has a slight curvature as seen in figures 3 and 4, and the wave can

become more linear by increasing the capacitance and decreasing the resistance in the integratingcircuit respectfully. The circuitry as seen in figure 5 is very complex and took a lot of time and effort to

put together. Furthermore, this also opens up possible loose wiring issues and short circuits and this can

be avoided by fabricating a PCB which would eliminate the vast array of wires and the possible loose

connection or short circuit.

Frequency Magnitude Shifted Magnitude Shift degree

Theoretical 50 Hz 2 Vpeak-peak 1 Vpeak-peak 1 V

Experimental 50 50.5 Hz 2.12 Vpeak-peak 1.28 Vpeak-peak 1 V

Table 1

Figure 5


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Application

Triangle waveforms are used highly in angular position sensors in many applications but one in

particular is the INCA Contact-Less Angular sensor [2] which is used in space telecom missions. Utilising

several Hall Effect sensor probes in conjunction with an operational amp configuration which outputs

several amplified and shifted triangle outputs. This is a cost effective way of mechanical sensors as it is

completely analogue. Furthermore in this application the op-amp configurations are utilised to amplify

the signal to sufficient voltage magnitudes to allow the signal to be analysed through another integrated

circuit design. The op-amp configurations are also used to shift waves to output signals in real time and

to compensate for external influences that can have an effect on the accuracy of the signal such as

temperature as seen in figure 6.

Figure 6 [2]


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Reference List

1. Lazaridis, G. The Schmitt Trigger. 2009 [cited 2011 25/10/2011]; Available from:

http://pcbheaven.com/wikipages/The_Schmitt_Trigger/.

2. Fabio Giacinto Nardone, A.D.C., Luca Ghislanzoni, Giorgio Parzianello(THE INCAS PROJECT: AN

INNOVATIVE CONTACT-LESS ANGULAR SENSOR, 2011. p. 8.3. Naveen John, V.R., DESIGN OF A TRIANGLE WAVE GENERATOR, 2006, Purdue Institution. p. 15.

[3]
http://pcbheaven.com/wikipages/The_Schmitt_Trigger/http://pcbheaven.com/wikipages/The_Schmitt_Trigger/http://pcbheaven.com/wikipages/The_Schmitt_Trigger/

Triangle Signal Generator

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