As the glucose measure probe to be used as reference has not been delivered for the expected time (just a couple of days ago) it has been moved as part of the Meditech phase 1 It is the worth to start do explain what is the adopted principle and what is the kind of analisys.
The following image shows a general view of the reference device. it cost on the market if you are not diabetics almost 2/3 of the entire cost of a complete Meditech unit, so I had to spend some time to find a way to have a full working device and accessories with a more reduced investment (about 100$)
The analyser (the biggest one in the image above) calculates the glucose percentage in the blood (a small drop of blood is needed from a finger, but we can assume this as non-invasive) The small needle is managed by a simple use mechanical device that "shoots" few mm the needle in the skin. Needles are single-use sterile parts that are the "bullet" of the mechanical device.
Usage steps
The glucose measure in diabetic patients should be done frequently several times during the day; usually they should measure by their own with a similar device the glucose value in the blood when eating to self-calculate the insulin quantity they should inject to compensate their disease. Meditech glucose probe will replace the measurement device (providing more complete information) and should be able to adopt the same methodology in glucose measurement. This makes simple to use the needles and chemical reactive already available on the market and worldwide diffused; can be found without difficult anywhere.
The first step is producing a blood drop with the mechanical "shooting" needle, usually in a finger. Depending on the age of the patient and his body characteristics the needle pressure can be regulated to minimise the pain (that is anyway almost null). See the detail in the image below
The second step is placing a drop of blood on the reactive test strip, that is another single-use small electrode chemically treated as shown in the detail of the image below.
Then, the reading procedure will start. As mentioned, the Meditech glucose measurement circuit will respect the reactive test strip size and contact positions and the accessory components (available in any farmacy as spare parts for few dollars) will be the same, just to grant the full compatibility of the methodology for two reasons: a better comparison testing with volunteers and the best standardised compatibility with the commercial devices.
The Meditech Glucose probe
The approach that will be followed by the Meditech glucose measurement probe will be based on the standard test strip terminals as shown in the PCB terminal layout example below:
The sensor circuit schematics using the pre-built test strips will be almost simple:
The circuit blue blocks are almost common parts based on a low-pass filter similar to the same already used for the Heart Beat sensor and ECG, while the green blocks are a current-to-voltage specific converter IC from Freescale that has been adopted by many other similar measurement devices.