BloodWatch

Right, just starting to get back to this now after being pulled away by family stuff. Have picked up a Tsunami (basically an Arduino coupled with a basic DDS waveform generator and frequency/phase/amplitude detector). It is almost certainly too slow to pick up a decent glucose signal (or possibly anything) but it will let me get some of the basic ideas straight before I start designing PCBs, wrestling with high frequency signals, buying possibly pricey DDS chips and so on. Regardless I'll keep posting here.

I've had one or two offers of help/interest and I will be following these up too.

Been fairly busy recently with other obligations. As a result not a lot of progress has been made. What I HAVE managed is:

• Gotten the waveform generator and phase/amplitude detector soldered not breakout boards.
• Wired everything up on a breadboard with an Arduino clone to test things out.
• Gotten a basic heartbeat (sine wave) using a 16MHz clock generated by a CMOS Schmitt trigger chip driving the waveform generator - note not being controlled by Arduino at this point.
• Switched to a clock generator breakout from Adafruit so I could drive the waveform generator at 75MHz; thought this would give better results than the jury rigged crystal+CMOS chip.
• Struggled to get ANYTHING to work with this setup. Unable to get waveform generator to respond to Arduino or generate clean output.
• Realised that breadboarding circuits running at 75MHz is PROBABLY NOT going to be successful.

So there we are. I think I'll try dropping everything down to maybe 1MHz max and see how that goes. The breadboarding is largely to validate how things are wired up, although I had hoped to do some measurements too. Have to see on that. This being my first project involving high frequencies AND a significant analog signal portion, I knew there would always be a sizeable learning curve. As for when I'll have time, that's less clear.

Well, I finally have the parts to proceed to the breadboard stage; waveform generators (both low and high speed), phase/gain detectors and breakout boards to match. I'll be soldering them up this weekend and start working towards having the low speed waveform generator and gain phase detector on a breadboard talking to an Arduino (at this stage I'm after easy to work with; speed, features, form factor and power usage will come when I proceed to prototype).

I've spent a little time looking at what I can find on the web about Dielectric Spectroscopy, in particular in relation to glucose. I've not yet found the ideal range of frequencies for glucose detection; one source suggests as much as 80MHz, while another as low as 40kHz. The higher the frequency the harder things get. Also, I need to get some experience of the technique and tech in general. So, plan is:

• Start with breadboarding/test equipment to create a minimal dielectric spectroscopy setup.
• Start at low frequencies (tens of Hz) and work up (to tens of MHz).
• Test different electrode styles and evaulate their response (I can think of three styles already).
• Test using known materials in solution (plain water, saline, glucose, possible blood itself) and characterise their signatures across different frequency ranges.
• Test using a running solution (flow through tubing) at different rates and characterise impact this has on the signature. Include case where some material within scope of electrode is NOT affected by flow.

I have more or less settled on an initial architecture for the device; a discrete waveform generator coupled with a discrete phase/amplitude detector, both of which are coupled to a basic micro controller. At this stage this doesn't need to be that powerful; a simple Arduino will even do (I can solve for what micro controller and bluetooth hardware to use latter).

If I move forward then the waveform generator may be replaced with something more basic (all I need is a sine wave with a frequency I can control and which covers the desired range).

So, I've ordered the following bits to start with. Will be a few weeks before they arrive.

• AD8302 Phase/amplitude detector (small and cheap)
• AD9954 High-end DDS waveform generator (large and pricey, 400MSPS, 200MHz max output)
• AD9834 Mid-range DDS waveform generator (small and cheap, 75MSPS, 37.5MHz max output)
• Signal Generator Module (0-40MHz, based on AD9850 - saves time during the bench testing phase)

In the meantime I'll use my other projects to learn more about SMD design/assembly so when the time comes I'll be able to make this into something reasonably compact and wearable!