Question

Draw a schematic for a DPDT switch and show how it can be wired to switch two separate circuits on and off.

: Why is it not possible to connect sensors such as thermocouples, strain gages, and accelerometers directly to a digital computer or microprocessor?

: What is successive Approximation, discuss them in detail.

Answer 1

Double pole Double Throw Switch:

It has two inputs and 4 outputs, and each input has 2 corresponding outputs respectively that can be connected to it.

Here each terminal of the input can be either in 1 of the 2 positions.therefore because of this the two inputs can be connected to 4 different outputs, and thus it can reroute a circuit into 2 different modes of operation. Either ON or OFF.

Example

Here whenever the switch is ON it will allow the circuit to be in one of the two modes.

thus when switch is flipped ON (upward) lamp and LED are ON and they will glow.

and when switch is flipped downward the buzzer and speaker are turned ON. and Lamp and LED are OFF.

2.

we cannot connect sensors such as thermocouples, strain gages and accelerometers to digital computers and microprocessor because these are analog sensors .they provide output as numbers as in values ..like for thermocouple in terms temperature (degrees and kelvin).. and before giving the signal to the digital computer the signal had to be conditioned, filtered, smoothed, and scaled first, then converted to a digital value before the microprocessor would even look at it.

and also a microprocessor or a digital computers accepts data in terms of 0 and 1. they cannot understand the analog results that are fed to them, therefore we cannot connect these sensors. other than that we can connect Analog front Ends (AFE) that are built by tesla as an answer to the problem, like the LMP90xxx series handles temperature of the thermocouple.

3.

successive approximation:

Before knowing that we need to understand what is analog to digital converter, in this the continuous analog signal is converted into discrete digital signal as 0 and 1 s .

And successive approximation ADC is a analog to digital converter which converts continuous analog signal to digtal values via binary search through the posssible quantization values( calculating output from a large set of inputs and rounding off to smaller or countable values).

this is a successive approximation circuit with the following contents

• DAC = digital-to-analog converter
• EOC = end of conversion
• SAR = successive approximation register
• S/H = sample and hold circuit
• V_ref = reference voltage
• V_in = input voltage

here we have many smaller sub circuits like the sample and hold circuit to obtain input V_{in ,}the voltage comparator which compares the V_in with the output of the internal DAC and gives the difference to the SAR register. and the SAR subcircuit designed to supply an approximate digital code of V_in to the internal DAC.An internal reference DAC that, for comparison with V_REF, supplies the comparator with an analog voltage equal to the digital code output of the SAR_in.

The SAR is initialized so that the most significant bit (MSB) is equal to a digital 1. And that code is fed into the DAC, which will then supplies the analog equivalent of this digital code (V_ref/2) into the comparator circuit for comparison with the sampled input voltage. If this analog voltage exceeds V_in the comparator causes the SAR to reset this bit; otherwise, the bit is left as 1. Then the next bit is set to 1 and the same test is done, continuing this binary search until every bit in the SAR has been tested. The resulting code is the digital approximation of the sampled input voltage and is finally output by the SAR at the end of the conversion (EOC).

Mathematically, let V_in = xV_ref, so x in [−1, 1] is the normalized input voltage. The objective is to approximately digitize x to an accuracy of 1/2ⁿ. The algorithm proceeds as follows:

1. Initial approximation x₀ = 0.
2. ith approximation x_i = x_i−1 − s(x_i−1 − x)/2ⁱ.

where, s(x) is the signum-function (sgn(x)) (+1 for x ≥ 0, −1 for x < 0). It follows using mathematical induction that |x_n − x| ≤ 1/2ⁿ.

As shown in the above algorithm, a SAR ADC requires:

1. An input voltage source V_in.
2. A reference voltage source V_ref to normalize the input.
3. A DAC to convert the ith approximation x_i to a voltage.
4. A comparator to perform the function s(x_i − x) by comparing the DAC's voltage with the input voltage.
5. A register to store the output of the comparator and apply x_i−1 − s(x_i−1 − x)/2ⁱ.