Ok for the curious kind, here is the brief overview of the machine.
Graded rice contains a lot of foreign bodies (small twigs, husk, dark
rice, bites tc) So, the job of the color sorting machine is to remove
out all these unacceptable particles from rice.

So, the grains from a silo are fed into a feed hopper, which feeds
A Vibrator (the construction of which is strikingly similar to the
images posted by Thomas Lehmann in the "Re: [EE]: First: Orienter w
electromagnet ViBRATOR" thread, The only major difference is in the
driving circuitry). This falls on a 1.2 meter long chute, where the
grains form into a singular stream. This stream passes through a
illuminated chamber, where
the grains are scanned against a background by the photodiodes through
the
associated optics and the signal goes to the processing circuitry.

The Ejectors, which fire out the unwanted grains by a burst of
compressed
Air is located about 1.5" below the scanning chamber. The electronics is
Way too fast for the mechanical ejectors. So, we introduce a delay
between
The sensing and the pulse output to the ejectors. This is done using a
chain of shift registers and clocked by a precise oscillator (you get
the idea!).

That's the rough Idea. As far as the scan rate is concerned, we need an
output of 35 kgs/hr from one channel (that's the limit on the old
design)
And the whole machine has 10 channels (350 Kgs/Hr). So roughly 400
grains
Pass in a second. So, a scan rate of atleast 800 Hz is required.

The arrival rate can and will be varied, to adjust with the varying
plant capacity and the overall plant throughput required. But every time
the arrival rate is varied, the time delay is to be varied. That's
roughly done on trial and error basis. And the delay also needs to be
varied whenever the
Grade of rice is changed, generally, the higher the grade, the heavier
the rice.

To conclude, this is nothing analytical, Its an industrial machine. So
the operator will generally be a dope with no knowledge of electronics
whatsoever. But the delay and the gain settings on the analog system are
A little hard to master. So I just want to make the system as easy to
operate as possible with ready made presets for all grades of rice.

Jeethu Rao

> -----Original Message-----
> From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU]
> On Behalf Of Russell McMahon
> Sent: Tuesday, October 22, 2002 5:22 PM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [EE]: Maximizing ADC Range
>
> > Hi,
> >  I'm working on improving(actually reimplementing) an existing
> >  analog Circuit using an MCU. Its  for a grain color sorter(used for
> > sorting rice)
>
> Curious minds (there are a few of them here :-) ) want to know Why?
> Is this for bulk rice sorting (I imagine not as the speed of response
> required would be immense) or (more likely?) for analytical work on a
> small
> sample?
>
> Companion questions:
> How often do you have to "measure" a new rice grain and typically how
long
> is the reading stable for?
> Have you got control of the arrival rate or does the arrival rate of
the
> grains vary widely?
>
>
>         Russell McMahon

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