[chbot] Lego Minstorms nxt open information

Charles Manning manningc2 at actrix.gen.nz
Tue Sep 2 23:02:49 BST 2008

On Wednesday 03 September 2008 08:32:39 Richard Jones wrote:
> I've attached the mindstorms light sensor schematic and I've not made much
> sense of it yet, anyone understand how it works? It appears to use current
> mirrors and a 3.1ms time constant. I'm not even certain whether the output
> to the nxt brick is current or voltage.
> Richard

I'm mainly digital, so I won't give a deep analysis, but my expectation is 
that the main purpose of the time constant is to take the edges off really 
bad noise such as florescent lighting. 

This is a reasonably high precision light sensor as it is used to be able to 
distinguish shades of grey etc.

The output is a current into a 10k pull-up internal to the NXT, and from there 
as a voltage into the ADC.

If you want to try to make a very simple sensor then use a LDR. LDR goes 
between pins 1 and 2 and short 2 and 3 together. It won't be very linear, but 
it should work. LDRs are also pretty slow which means there is no need for 
any filtering.

-- CHarles

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