The simple current input to voltage output opamp has a positive and negative output. You never said a positive only output.
The digital circuit must not have a negative input. Also it needs a logic input voltage higher than 2V.
Now your entire project makes no sense.
ok full detail of project is as follows
Detail of the task
Analogue:
A remote motor speed sensor provides a current signal in the range of -2.5 to 2.5 mA. Design a circuit to convert this signal into a voltage signal in the range from 2 to 3 V. After the conversion, a low pass filter is used to suppress any noise AC signals with frequency higher than 50 Hz.
Digital:
An 8-bit analogue-to-digital converter will be given and should be used to convert the output of the above analogue circuit into an 8-bit digital signal. The 8-bit signal should go through two 4-to-7 decoders so that the value of the 8-bit digital signal is displayed as two hexadecimal values on two seven-segment display devices to indicate the safe running speed of the motor in range 0-255 (i.e. 00hex to FFhex).
Part 1: Design a current amplification and filtering circuit [40 marks]
Use an AC current source with a very low frequency of 0.01 Hz to emulate the slowly changed current output signal from the remote motor speed sensor. Design the current amplification circuit using appropriate op-amp circuits so that you can achieve the required output voltage (2 to 3 V). Demonstrate the gain, Bandwidth, Rin of your op-amp circuits by both calculation and simulation.
Design the low-pass filter. Demonstrate the bandwidth of the filter by both calculation and simulation.
Combine the op-amp circuit and the filter. Demonstrate the gain, Bandwidth, phase shift, Rin of your combined circuit by both calculation and simulation.
Marks allocation:
- Current sampling/amplification circuit: [15 marks]
- Low-pass filter circuit: [15 marks]
- Combined circuit: [10 marks]
Part 2: Design an 8-bit counter and a 4-to-7 decoder for the Seven-Segment display [40 marks]
The output voltage signal from the analogue circuit should then be converted into an 8-bit digital signal, which represents the levels of the motor speed. You can choose the generic 8-bit ADC device from the Proteus library => Modelling Primitives => ADC_8 for this task. Following is an example connection of the ADC convertor that you can refer to when you design your circuit.
2.1) 8-bit counter design
Design an 8-bit synchronous counter by using D-type flip-flops. The counter should be driven by a CLK signal running at 256k Hz. You should show how the counter is designed, and simulate the circuit.
Marks allocation: [15 marks]
The MSB output of the counter should be used to connect to the clock terminal of ADC_8 converter. The value of the output of the ADC_8 converter should be displayed in two 7-segment display units. The MSB four bits are displayed in one and the LSB four bits in another 7-segment display. In order to achieve this, you should design the 4-to-7 decoder for the 7-segment display, as detailed below.
2.2) 4-to-7 decoder design
A 7-segment display decoder is commonly used to display a particular number representation using a display composed of seven LED segments. The diagram below represents a 7-segment display decoder which converts a 4-bit binary number into a collection of symbols to be displayed:
Your 7-segment decoder should accept a 4-bit binary numbers [x3, x2, x1, x0], which represent integer numbers 0 - 9 and letter A, B, C, D, E, F (i.e. which represent hexadecimal value in range 0hex to Fhex). A 7-segment display with common anode should be used, i.e. the decoder should output “0” to switch on the corresponding LED segment (a-g) of a 7-segment display shown above. The symbols used should be:
Complete the truth table for the 4-to-7 decoder: Use Karnaugh map to simplify the logic expressions for the 4-to-7 decoder. You can use all available gates (some of them are listed below). Simulate your decoder circuit and demonstrate that the circuit is working properly.
Marks allocation: [15 marks]
2.3) Combined digital circuit
Connect the outputs of the 8-bit ADC to two 4-to-7 decoders which drive two seven-segment display units, respectively. Simulate the circuit and demonstrate that entire circuit works properly.
Marks allocation: [10 marks]