Archive for the ‘Medical electronics’ Category.

Affordable pH meter

Our home vineyard delivers about 1000 liters of wine every year. It takes some effort to keep good quality and pleasure for all friends tasting the must, new wine and “senior” wine reserves. One of the most important tasks in wine quality management is controlling the biological and chemical state of the wine. The wine can be monitored in special laboratory or in home lab. Of course home lab become rational when quantity of the wine is high enough to justify expenses in special equipment.  There is some low cost equipment available for wine analysis, mostly with titration techniques, but chemical lab equipment is rather expensive and many hobby wineries avoid buying such equipment. I hope this post can contribute a bit to change that. I will describe the development of simple pH meter in detail.

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Biomedical signal sources

Biomedical signals originate from different sources. Bioelectric signals are generated by nerve and muscle cells. Each single cell under proper condition may generate an action potential, which is measured at single cell level or with more gross methods, where the electric field generated by the action of many cells is measured with surface electrodes at the body surface.

Bioimpedance signals are generated within tissue when excited by AC currents. The measurement is conventionally performed with four point method. Impedance changes are result of a tissue composition, blood volume and distribution, endocrine activity, sympathic nervous system activity, and other phenomena influencing body impedance.

Biomagnetic signals are generated by various bio-systems and organs. They generate weak magnetic fields which provides information not obtainable from other biosignal sources, like bioelectric signals. Biomagnetic signals has very poor signal to noise ratio

Some biomedical processes generate bioacoustic signals. These signals are usually acoustic noise. The measurement of noises provides information about underlying system. Typical noises are generated by blood flow of through the heart or hearts valves and blood vessels. Measurement of acoustic sounds generated by air flow through airways and lungs is one of the most important vital signs monitoring methods used also for special monitoring procedures. Characteristic sounds are also generated by digestive tract, joints, muscles or during pregnancy.

Biologic systems may generate Biooptical signals naturally or as a result of optical stimuli. Blood flow or blood oxygenation may be measured by light transmission and reflection at different wavelengths. Propagation of the fluids may be estimated when fluids are diluted with dye and dye appearance is measured with minimally invasive sensors like optical fibres.

Biomechanical signals are signals generated by displacement, pressure, tension, flow and others. Main difference between biomechanical and other signals is the biomechanical phenomenon does not propagate like electric and magnetic fields or acoustic signals through the tissue. This enforces invasive measurement techniques.

Chemical reactions between tissue or other live samples and other reagents usually result in different ion concentrations. Biochemical signals are result of such ion concentration deviation measurements performed with dedicated ion electrodes. Changes induced by biochemical reactions are in range of several seconds or minutes and could be treated as ”almost” DC signals.

New section – medical electronics

Medical electronics, mostly sensors, more specifically, Invasive blood pressure sensors are my professional occupation for last couple of decades. I gained some experience which I would like to share here. All new posts related to medical applications will have own category with some sub-categories which I will add “on the fly”. I will explain some basic sensing principles for several parameters measured on human (or animal) body. I will add some practical circuits I realized during my PhD study and could be interesting for hobby use.meddev

I am really passionate about developing flexible, affordable and innovative solutions for healthcare, mostly low power and some simpler circuits or use of existing devices non-conventionally. My humble wish is that my expertise could be helpful to someone who visit my site.

Important information (disclaimer):

DisclaimerThe information contained in this website is for general information and educational purposes only. None of the circuits or other information presented in this site must not be used in any safety-critical applications (such as life support, diagnostic, therapetic treatment, etc…) where a failure of the presented circuits would reasonably be expected to cause personal injury or death. The readers and visitors of my site shall fully indemnify authors on this site against any damages arising out of the use of any circuits presented in this suite in such safety-critical applications . The reader of this site shall ensure that it has all necessary expertise in the safety and regulatory ramifications of its applications and the reader shall be solely responsible for compliance with all legal, regulatory and safety-related requirements concerning its products and any use of any information presented in this site own applications, notwithstanding any applications-related information or discussions that may be provided by this site.