Design Article
Electronics in medical apps: Fertility monitor design
Asha Ganesan, Cypress Semiconductor
2/20/2013 1:01 PM EST
Design of a fertility monitor system using SoC
A fertility device can utilize 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.
Figure 4: Block diagram of a fertility monitor in a programmable SoC
Click on image to enlarge
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 color/ 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 (refer to 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 analog 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 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.
The resolution of the ADC depends upon the characteristics of the photo-diode used and also on the actual measurement accuracy needed for the application.
Next: Power management
A fertility device can utilize 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.
Figure 4: Block diagram of a fertility monitor in a programmable SoC
Click on image to enlarge
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 color/ 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 (refer to 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 analog 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 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.
The resolution of the ADC depends upon the characteristics of the photo-diode used and also on the actual measurement accuracy needed for the application.
Next: Power management
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eewiz
2/21/2013 11:31 AM EST
Haha interesting application... Will be useful in some Asian countries with very low fertility levels.
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Asha Ganesan
2/21/2013 12:32 PM EST
Thanks! In today's world many women are looking for such equipments.
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EREBUS
2/21/2013 3:36 PM EST
With our current population growth I fail to see how helping more women get pregnant is a benefit. Now if you use it to help women AVOID getting pregnant, we can help lift a lot of people out of poverty.
Just my opinion.
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Etmax
2/23/2013 12:08 AM EST
An interesting view of the presented work, and something actually does work, such methods are used as an alternative to the pill (not LH measurement, temperature). It also has the benefit of reducing the likelihood of birth defects which given the impact on families and the community is another noble cause. Yes we should be reducing the world population (preferably to around 2billion) but if we don't reinvent our economy I'm afraid the outcome may be almost as undesirable.
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eewiz
2/21/2013 9:18 PM EST
@ EREBUS this is not the case in everywhere.. if you look at places like hongkong/japan/korea/singapore the TFR(total fertility rate) is much lower than the replenishment rate of 2.1. ie..these countries can potentially get wiped off in future. Ofcourse the main reason is social and cultural and not medical. but then, there is a small percentage who will have medical/stress related problems to whom things like this could be helpful.
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Asha Ganesan
2/22/2013 11:32 AM EST
@EREBUS: Yes, this system can also be used by women who do not want to get pregnant. This can avoid the usage of contraceptive pills which may have some side effects.
@EEWIZ: Thanks for providing this statistical information. This is absolutely correct. I think designing such gadgets would be of great use in those Asian countries.
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