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Developing a fertility monitor

Posted: 11 Mar 2013 ?? ?Print Version ?Bookmark and Share

Keywords:health monitoring systems? fertility monitor? basal body temperature?

B. BBT measurement:
Here a good quality temperature sensor is used to measure the woman's body temperature every morning. As shown in figure 2, the BBT remains low before the ovulation day. A sudden hike of about 0.2-0.3C in the basal body temperature measurement indicates that the ovulation day should occur in a day.

Fertility monitor system design using SoC
A fertility device can utilise either the LH-testing or BBT testing methodology. For higher precision testing, both can be included. Figure 4 shows a block diagram of this application.

Feeding input from the LH test strip and the temperature sensor
As discussed earlier, in the LH testing, the tested band and the reference band's colour/ darkness need to be compared to measure the result. Therefore, a few external LEDs driven by a particular voltage using a VDAC (can be mux-ed or driven always) are needed to make light rays fall on the test strip. The light is absorbed by the bands on the strip, depending upon their darkness.

The tested LH strip is placed in between the plane where the LEDs are placed and the plane where two photo diodes are placed (figure 5). In general, the photo-diodes are placed just below the position where the test band and reference band appear. The two photodiodes corresponding to the test band and reference band generate currents depending on the intensity of the LED light falling on them. These photodiodes are connected to a trans-impedance amplifier to convert the current readings to suitable voltages, which are then fed to a Del-Sig ADC through an analogue MUX for further processing.

A temperature sensor such as an RTD can be connected externally that feeds the sensed BBT reading (which is also muxed along with the photo-diode readings) to the ADC.

Figure 4: Block diagram of a fertility monitor in a programmable SoC

Figure 5: Placing LEDs and Photo-diodes above and below the LH test pad.

The digital output of the tested band and reference band readings are compared and, if the reading of the tested band is lower than that of the reference band, this means the test band has darkened more than the reference band and the ovulation period has been reached.

For the BBT method, the range of the digital equivalent of the BBT values during ovulation is stored permanently in Flash or EEPROM as a reference value. The measured BBT value is compared to the reference value and the fertility level is noted.

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