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High CMRR Instrumentation Amplifier (Schematic and Layout) design for biomedical applications

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Instrumentation amplifiers are intended to be used whenever acquisition of a useful signal is difficult. IA’s must have extremely high input impedances because source impedances may be high and/or unbalanced. bias and offset currents are low and relatively stable so that the source impedance need not be constant. Balanced differential inputs are provided so that the signal source may be referenced to any reasonable level independent of the IA output load reference. Common mode rejection, a measure of input balance, is very high so that noise pickup and ground drops, characteristic of remote sensor applications, are minimized.Care is taken to provide high, well characterized stability of critical parameters under varying conditions, such as changing temperatures and supply voltages. Finally, all components that are critical to the performance of the IA are internal to the device. The precision of an IA is provided at the expense of flexibility. By committing to the one specific task of
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PWM based temperature controller using ATmega16A

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Abstract: In this project we are going to design an embedded system that controls the temperature using a PWM signal, generated by a ATmega16A controller. 

Here we assume that our required temperature is 145 degrees C' and the bandwidth is ∆T= 20 degrees C. And also assume that it takes 10sec to heat up to 145 degrees C(this is not true in all cases). With  ∆T= 20 degrees C maximum temperature is 155 degrees C and minimum temperature would be 145 degrees C. Duty cycle can be calculated using the following formula..
                T_duty =1- (T_sensor – T0)/∆T
                   here T0=145 degrees C and T_sensor is the temperature sensor output
If you want to control higher temperatures, say above 150 degree C, then you have to use Thermistors instead of LM35. Here 10*T_duty gives the ON time duration and 10*(1-T_duty) gives the OFF time duration.

Operation:- The temperature sensor will sense the temperature of the device/chamber and a Nichrome wire used as a Heating element. Here LM35 is connected to the internal ADC0 pin of ATmega16A controller. ADC output will be the T_sensor value and is used to calculate the T_duty cycle period. PD0 pin carries the PWM signal, is connected to the Nichrome wire. If there is a change in temperature T_duty will change and the PWM will change. Example, if the temperature is higher than the required then the T_duty (ON time) will be reduced and OFF time will be increased to cool down the temperature. If the temperature is lower than the required then the T_duty (ON time) will be increased and OFF time will be reduced to increase the temperature.   
When the temperature is 144 degrees C 
       T_duty = 1-(144 - 135)/20 = 0.55*10=5.5sec = ON time
       1-T_duty = 1-0.55= 10*0.45=4.5sec = OFF time
 When the temperature is 150 degrees C 
       T_duty = 1-(150 - 135)/20 = 0.2*10=2.5sec = ON time
       1-T_duty = 1-0.25= 10*0.7=7.5sec = OFF time

Flow chart:-   to download the source code

NOTE: The time required to heat up to a required temperature will depend on the type of heating material used. Calculate the time required and use it to generate PWM. 


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