Assessment item 3—Design Assignment
| Due date: | Wednesday of Week 12 |
ASSESSMENT |
| Weighting: | 35% |
3 |
| Length: | N/A |
Details
A strain gauge is used in Wheatstone Bridge configuration. The output from the Wheatstone Bridge varies from zero to a maximum strain output of 12V, that is it is in the positive quadrant.
You are required to convert this 0 -12 V analog signal into a 12 bit digital signal (Analog to Digital Conversion, ADC). The maximum frequency of the analog signal is 20 KHz (this governs the Nyquist sampling rate).
- The relationship between the analog value of the digital signal and the input analog signal is such that it obeys the square law. The functional relationship is exhibited by the digital step having a greater sensitivity at the low voltage levels than at the higher voltage level (the analog equivalent of the digital step is smaller at the lower voltage levels than at the higher voltage levels).
- The resultant digital signal is also converted to the Gray code in that only one bit is to change for each quantisation level change.
- The output of the ADC or the Gray code equivalent is used to illuminate three lights using combinational logic to give
Green > 1/2 Vmax (stays on while the voltage is exceeded)
Amber > 3/4 V max (stays on while the voltage is exceeded)
Red >7/8 Vmax (stays on while the voltage is exceeded)
- The Digital signal is converted back to an analog signal but each digital bit step increase has the same analog magnitude change, the digital signal is considered a linear function of voltage.
Each component (bullet point above) of the total design is to be simulated using:
NI circuit design suite (Student edition or Academic edition)
National Instruments
Your report should follow a standard report format and include but not limited to:
- The simulation files
- Documentation of the simulation
- Printed schematic
- Indication of the design process
- Appropriate images that illustrate the output function of the design
Assignment Assessment Criteria
All assignments must be submitted through hard copy submission. The assignments will be graded using the following criteria:
- Satisfying the design criteria;
- Appropriate minimisation of components in the design;
- Well structured design report,
- All working must be shown to obtain marks;
- Assignment must be neat, tidy and legible.
SOLUTION
ANALOG TO DIGITAL CONVERTER—
BINARY DECIMAL GRAY CODE
0000 0 0000
0001 1 0001
0010 2 0011
0011 3 0010
0100 4 0110
0101 5 0111
0110 6 0101
0111 7 0100
1000 8 1100
1001 9 1101
1010 10 1111
1011 11 1110
1100 12 1010
Gray codes corresponding to 6,9 and 11 are changing for the lights green,amber and red.
A4 is 0 when there is green.A4(MSB,4th bit) changing from 0 to 1 when green to amber ,A2 (2nd bit) changes 0 to 1 when amber to red.Connections will be taken from the connections between counter and digital to analog converter.
We can use different logic gates for this conversion.
In figure counter and digital to analog converter is of 8 bit. Instead of this 4 bit of these will be used.As these are not available in software so these are shown of 8 bit.
For squre relationship μ-law may be used.(from wikkipedia)
LH57
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