COMPLETED TASKS DURING THE PERIOD

1.Debug the previous final circuit errors

By considering power input of the above schematics diagram,

+9V/-9V dual power supply circuit was planed to use for this circuit. So above main circuit must need input power socket with three nodes(Positive pole, Negative pole and GND pole). But DC005 -2.0MM socket that is used above diagram is not suitable for this circuit. We need to replace it with better power input socket such as JST 1*3 connector.

When we using 7805 voltage regulator, there is a high voltage drop across the regulator. It is the power wastage. Higher input voltage (9V) is one of the reason for high voltage drop across the regulator. Also diode before 7805 is not essential thing. Also there is a high voltage drop across the 3.3v regulator(LM317). But we must need 3.3V regulator for wifi module. Because operating voltage of the wifi module is 3.0V to 3.6V. As a answer for this situation, we can reduce the input voltage from 9V to 6V.

By considering amplifier circuit,

According to circuit calculations if we need to get better performance from this amplifier circuit, there are some adjustments that we need to do. Following are these adjustments,

1. Reduce gain potentiometer resistor value from 50k to 5k.

2. Reduce sensor bridge balancing potentiometer resistor value from 50k to 10k.

3. Correct the TIP30 transistor pin connections.

4. Increase gain potentiometer value of the 1st stage op amp.

5. Add the 2nd stage amplification part.

6. Remove 16bit ADC converter module connector from the circuit. Because we can use Atmega328p microcontroller ADC channels.

By considering Atmega328p microcontroller part,

Operating voltage range of the Atmega328p microcontroller is 1.8V to 5.5V. So 6V input power can be harmed to microcontroller. Hence we can use 5.6V Zener diode with current limiting resistor to overcome this problem. Also a capacitor can be added across the output to reduce noise effects.

2.Solutions for better performance of dual power supply circuit

Firstly, we need to convert this circuit from +9V/-9V to +6V/-6V. There is higher power wastage in this circuit. Because there is high voltage drop across the 7809 , 7909 positive and negative voltage regulators. Following are the some of the solutions to overcome these facts.

Why we need more secure and patient friendly power supply for medical device?

Reducing noise in medical equipment, especially when that equipment installed in the non-clinic environment becomes a must and manufacturers are now building their equipment to reduce the level of noise clause to inaudible, limiting forced ventilation to excellent condition.

For power supplies manufacturers that implies that power supplies will be operated with cooling limited to conduction and convection, requiring power designers to optimize performances while keeping in mind reliability in such environment (we all know that MTBF decreases with temperature)!

Patient Safety is also a significant aspect that power supplies designers have to consider and knowing that studies revealed that 60% of the homes in Europe and 40% of those in the U.S. have no reliable ground wires, it is essential to protect users of home medical devices from electrical shock. Powering Home Healthcare equipment with safety is what standards and regulations are for sure addressing but as well something all power designers have in mind when developing power solutions for medical applications and especially home healthcare.

Power safety standards of power supply for medical devices

Safety is a significant concern and medical power supplies must comply with the standard IEC 60601 published in 1977; the standard that is internationally adopted (see figure 1) and continuously updated to improve patient safety and comfort. More detailed information can be found from the different standardization organizations, but it is interesting to quick look at the two revisions that impacted on the implementation of new technologies power designers have to consider guaranteeing the highest level of safety for patient and operators.

In 1988 the second edition introduced three categories specifying specific conditions under which the medical equipment, including the power supplies, are operated in patient vicinity (1.83 m (6 feet) beyond the perimeter of the intended locations, e.g., bed, treatment-area):

Type “B” (Body) No electrical contact with Patient

Type “BF” (Body Floating) Electrically connected to Patient but not directly to the heart

Type “CF” (Cardiac Floating) Electrically connected to the heart of the Patient.

Strengthening patient protection against electrical shock and effects of current leakage, the third revision introduced a more stringent requirement; defining the meaning of different protections for patient and operators. Means of protection (MOP) describes the isolation protection between the electrically charged circuitry and any equipment that may come in contact with the device.

The isolation protection includes the creepage/clearance distances, insulation, and protective earth connections. The means of protection is further separated into two categories (Means of operator protection MOOP and Means of patient protection MOPP) implying specific isolation test voltage and creepage distance (figure 2).

The third revision requires from power supply designers to perform a risk assessment analysis by the ISO 14971:2000 (Application of risk management to medical devices) to ensure that hazards are identified and mitigated to guarantee that the appropriate level of safety provided to the final application. For example, in medical equipment not in contact with the patient, a power supply complying with 2 x MOOP usually is acceptable though the outcomes from the risk assessment could steer the designer to increase the creepage distance to guarantee a higher level of safety for the patients and the operators.

IEC60601-1 third revision has introduced a new way of working, combining power design, risk assessment but as well an extreme level of cooperation with the equipment manufacturer to guarantee the proper level of safety to patient and operators.

This new approach becomes tangible in connection with the form factors of medical power supplies. Since the 3rd Edition external power supplies are considered as stand-alone medical devices, which requires from the power supply manufacturer a full risk assessment and documentation according to ISO 14971. On the contrary, for built-in power supplies, the medical device manufacturer is fully responsible for the risk analysis, for which a close cooperation with the power supply manufacturer is needed.