0
\$\begingroup\$

This is a drawing I made of a light sensor unit I'm creating. Inside of it, I have a circuit board containing 3 7-segment displays and I have two photo-transistors (yellow half-circles in the picture) sandwiched between the displays as well as other places on the board (I didn't include pictures of those ones in the diagram).

The parts are as follows:

Photo-transistors: PT334-6c 2 large 7 Segment displays (white box): 7S210012AS 1 small 7-segment display (green box): SM520501Y 1524

I provided measurements of almost every item.

Details of the large displays are at: http://futurlec.com/LED/7SR10012AS.shtml

Details for the Photo-transistors are at: http://www.everlight.com/file/ProductFile/PT334-6C.pdf

The other display I could not get details for because I ordered it from a chinese guy through Ebay.

The light sources that will be hitting this beam are 5mW red laser beams and IR emitters

I could not get any info on the laser diode. All I know from measurements is that a 90 ohm SMD resistor is fitted onto the laser diode module (that I also bought from Ebay)

Info on the IR emitters are located here: http://futurlec.com/LED/INF5940.shtml

I plan to use diffused plexiglass (shown as red in the diagram) to fit right on top of the large 7-segment displays so that when someone shoots the unit with the laser beam or IR emitters, the on-board sensors can react accordingly.

I was experimenting with resistor values in the past but based on research I was told using 560K resistors as pull up just may be too high.

So now I might as well go to the other extreme but I don't want to get too carried away with the lows or I'll be draining the batteries or blowing something up.

So what's the lowest resistor value I can use here if my circuit is the same as shown?

Now if I added say another 10 photo-diodes in parallel (so that if a shot is sensed by ANY photo-transistor, the circuit reacts accordingly), what would be the lowest resistor value I can use?

By react accordingly, I mean where the unit senses enough change in light to the point where the output of the schmitt inverter changes its level to the light-detected state.

Also, we have to assume the 7-segment displays all light up with the number 8 on them. Each segment is powered from 5V through 1K resistors with 5% tolerance.

light sensor

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Browse other questions tagged or ask your own question.