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struggling with CMOS optical sensor array

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kevinvw

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Hi, I am working with a TAOS tsl1401 128X1 CMOS Optical Linear Sensor Array and i am having trouble with clocking and SI trigger.

(I can't post URLs yet, but their site is taosinc.com)

Has anyone worked with one of these chips?

I am struggling to understand how the serial input trigger is supposed to be timed against the main clock.

I know this is a bit vague, but I am somewhat new to digital circuits so I'm not sure exactly what questions to be asking...

Thanks,

Kevin.
 
If you look at the Fig. 2 timing diagram on pg. 5 of the data sheet, you can seen that the SI trigger should go high when the clock is low.

It should go low tsu(SI) seconds before the clock goes high (20ns from pg. 2). It should stay high for th(SI) time after the clock goes high, which is 0ns from the data sheet (which means it can go back low as soon as the clock goes high).

Thus the SI trigger can change from low to high on the falling edge of the clock and from high to low on the rising edge. (The SI trigger should be low before the next clock rising edge)

The time between SI pulses should be at least 129 clock pulses.

You could use a counter, a flip-flop, and some gates to do this. You would enable the flip-flop for one clock-pulse every 129 clocks (or more) from the counter. The flip-flop would gate the (inverted) clock for one clock pulse, giving the desired SI pulse.

To understand and design digital circuits you should be able to read a timing diagram. It's hard to understand digital circuit timing otherwise. You might look at "digital timing diagram" in wikipedia or do a google search for more info.

All this make sense?
 
Hi Carl, thanks for the info.
I finally got back on the project.
I was able to figure it out.
One thing I did was buy a new cmos sensor chip.
I'm not sure if the one I was using was bad, but it was an older version.
The older chip required a pull-down resistor on the Analog out.
I got the newer chip working.
But it was probably more due to the fact that I got my arms around the timing
I was able to use my Aruduino (AtmelATmega168) microcontroller to create the clock and SI signals.
The only way I could figure out how to make sure that the SI signal was firing when the clock went low was to use a scope and put a slight time delay in between the initialization of the 2 PWM signals.
I'm still trying to figure out how to get the SI PWM to know that the clock PWM is low...

Thanks again.

Kevin.
 
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