[DIYbio] turbidity spec (was: DIY Science Equipment contest)

On 09/06/2013 03:53 PM, Sebastian Cocioba wrote:
> While still kind of on topic, what would you guys like to see in a
> turbidity spec?
>
> So far my plan is as follows:
>
> 3D printed chassis
> takes standard 12.5mm cuvettes (10mm path)
> ~3" tall 2" wide square footprint with lid

Small size is good. Lugs in some of the sides to use self tapping screws would be nice for integration.

> Tiny LCD screen and two buttons as stand alone unit for blanking and
> reading

Not sure what above means. Is it in two parts? knobs are great for adjusting a calibration -- button presses
can seem very slow. Are you planning cal as stand alone with least squares fit in microcontroller code,
or as a connected to a PC function?

> The whole device is an arduino Sheild with open source standard curve
> tools, simple GUI, logging, etc.

Logging via USB port or ?

>
> I was thinking of using a digi stump but it would drive cost up. The
> original plan was a stand alone battery powered module that can be
> placed anywhere and pocketed when needed.
>
> All software open source as well as design CAD, STL, OBJ, Eagle for
> sheild circuit, and parts list.

Why not KiCAD or gEDA PCB for defining the board? So the open design info
can be used with an open tool...

> I'm debating whether or not to include a built in generic arduino or
> keep it a sheild.
>
> The arduino's main clock is precise enough for 1Hz readings
Do you mean the time integrating and averaging for one reading finishes in 1 sec?

but I would
> be happier designing a op-amp clock a la 555 or edge counter chip for
> improved accuracy and precision. With some low level arduino code I
> managed to get the interrupts to work and the signal is fairly stable.

> Best readings are made by blanking for each sample.

Does that mean shuttering the optical path for calibrating zero for each measurement?
Seems unnecessary with some good use of A2D volt references and a good use of
microcontroller clocks at a MHz speed, and a cal once before a
series of measurements. There are MSP430 microcntrollers that sip on
battery power for years between batteries and have easy to use clocks and
timers for apps and for sleeping when not needed.

The code will be in
> Mono. Hope no one minds too much about that.

Sounds fine for your connected apps. For microcntroller code, C would be best.

John Griessen

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