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No way of bypassing this Lasertrigger circuit - and about calculating stuff
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HendriXML:
In your by lasers beams protected house of intellectual terror mission impossible Tom Cruise is comming for your very secret electronic designs. He bring his own set of lasers to satisfy the sensors, will he succeed or will it be impossible?

Not with this circuit! because it drives not one, but two resettable latches. One that signals when a laser beam is broken. One that signals that the sensor is exposed when it shouldn’t. Those states are alternatively checked by pulsing the laser beam at roughly 7 kHz.
If the beam is broken, the laser will for safety reasons shut down (it served it’s purpose anyway). This will as a side effect also trigger the other latch - I won’t remedy that. Another quirk is that it starts up being activated. Used with a micro controller a reset on both latches should remedy that.

I will search for a more suited photo diode, because the one I use has a very high impedance in exposed and non-exposed conditions. However the discrimination between the laser exposure and surrounding light exposure is very good. Measuring millivolts with high impedances and long leads make it now too sensitive for external interference. Besides that it really works well, especially using the triangle wave to disable comparisons during signal transitions.

The latches are also designed in such a way that a signal triumphs a reset.

So no one is crossing my beam  >:D.

Any comments or suggestions?
HendriXML:
Below I posted the calculations for this project. It uses a self-made scripting tool, which is able to define tasks. Within those tasks one can do calculations and simulations, or whatever. A task essentially produces / provides information to use either in schematics or for further calculations. The tool ensures every task is executed in the right order and only once.

Technically a task sets fields of a newly created object. Depended task can read those fields for further calculations. I always report what is "consumed" from that object. In this way it is very well documented how data travels and what is affected by what when things change.
There is also the possibility of creating asserts: states, values that you want to guard. If for example I tested a forward voltage on 20 mA, then I might want to ensure that the true current is calculated and checked against 20 mA. So when modifications alter the current, the task will fail. Giving the opportunity to do a new measurement and updating the forward voltage and current.

Creating such a script is a lot of work, but is also supports thinking in a very modular way.

The coarse dependency information NEEDS and NEEDED BY is generated, so no need to do that by hand.

In the near future I will probably upgrade the BOM scripts (https://github.com/HendriXML/KiCad-BOM-reporter) to report calculated values against schematic values.
HendriXML:

CHOOSEN VALUES
NEEDED BY
  Empirical values TL082
  Empirical values 1N4004
  Exposed sensor LED
  Break signal LED
  Laserdiode control
  Triangle wave voltages
  Virtual ground en reference voltage dividers
  Comparator latches
PROVIDES
  voltVCC                  : 5,00 V
  ohmR3                    : 100 kΩ
  ohmR6                    : 47 kΩ
  ohmR23                   : 4,7 kΩ
  ohmRV1                   : 1 kΩ
  ohmRV3                   : 500 Ω
  ampVirtGndVoltageDividerTarget: 7,00 mA
  voltVirtualGroundMargin  : 250,00 mV

DATASHEET VALUES 2N7000
NEEDED BY
  Laserdiode control
  Comparator latches
PROVIDES
  ohmOnResistance          : 6,00 Ω

EMPIRICAL VALUES 2N3906 Q3
NEEDED BY
  Laserdiode control
PROVIDES
  voltEC                   : 600,00 mV

DATASHEET VALUES 2N3906 Q3
NEEDED BY
  Laserdiode control
PROVIDES
  factAmplificationAt30mA  : 30,00 A
  voltBESat                : 700,00 mV

DATASHEET VALUES LM339
NEEDED BY
  Exposed sensor LED
  Break signal LED
  Comparator latches
PROVIDES
  voltLowlevelOutputVoltage: 150,00 mV

EMPIRICAL VALUES TL082
NEEDS
  Choosen values
NEEDED BY
  Virtual ground target voltage
  Triangle wave voltages
CONSUMES
Choosen values
  voltVCC                  : 5,00 V
PROVIDES
  voltSwingToGroundNominal : 40,00 mV
  voltSwingToVCCNominal    : 3,70 V

EMPIRICAL VALUES 1N4004
NEEDS
  Choosen values
NEEDED BY
  Virtual ground en reference voltage dividers
CONSUMES
Choosen values
  ampVirtGndVoltageDividerTarget: 7,00 mA
PROVIDES
  voltForwardVoltage       : 700,00 mV

EMPIRICAL VALUES RED LED
NEEDED BY
  Break signal LED
PROVIDES
  voltForwardVoltage       : 2,00 V
  ampForwardCurrent        : 20,00 mA

EMPIRICAL VALUES BLUE LED
NEEDED BY
  Exposed sensor LED
PROVIDES
  voltForwardVoltage       : 3,40 V
  ampForwardCurrent        : 20,00 mA

EMPIRICAL VALUES LASER DIODE
NEEDED BY
  Laserdiode control
INTERMEDIATE
  voltVoltageDrop          : 726,00 mV
  voltPackageVoltage       : 3,00 V
PROVIDES
  ohmSerieResistor         : 33,00 Ω
  voltForwardVoltage       : 2,27 V
  ampForwardCurrent        : 22,00 mA

EXPOSED SENSOR LED
NEEDS
  Choosen values
  Empirical values blue LED
  Datasheet values LM339
CONSUMES
Choosen values
  voltVCC                  : 5,00 V
Empirical values blue LED
  voltForwardVoltage       : 3,40 V
  ampForwardCurrent        : 20,00 mA
Datasheet values LM339
  voltLowlevelOutputVoltage: 150,00 mV
INTERMEDIATE
  voltR21                  : 1,45 V
  ohmCalcR32               : 72,50 Ω
PROVIDES
  ohmR32                   : 75 Ω

BREAK SIGNAL LED
NEEDS
  Choosen values
  Empirical values red LED
  Datasheet values LM339
CONSUMES
Choosen values
  voltVCC                  : 5,00 V
Empirical values red LED
  voltForwardVoltage       : 2,00 V
  ampForwardCurrent        : 20,00 mA
Datasheet values LM339
  voltLowlevelOutputVoltage: 150,00 mV
INTERMEDIATE
  voltR21                  : 2,85 V
  ohmCalcR21               : 142,50 Ω
PROVIDES
  ohmR21                   : 150 Ω

LASERDIODE CONTROL
NEEDS
  Choosen values
  Empirical values laser diode
  Empirical values 2N3906 Q3
  Datasheet values 2N3906 Q3
  Datasheet values 2N7000
CONSUMES
Choosen values
  voltVCC                  : 5,00 V
  ohmR23                   : 4,70 kΩ
Empirical values laser diode
  ohmSerieResistor         : 33,00 Ω
  voltForwardVoltage       : 2,27 V
  ampForwardCurrent        : 22,00 mA
Empirical values 2N3906 Q3
  voltEC                   : 600,00 mV
Datasheet values 2N3906 Q3
  factAmplificationAt30mA  : 30
  voltBESat                : 700,00 mV
Datasheet values 2N7000
  ohmOnResistance          : 6,00 Ω
INTERMEDIATE
  voltR4sInternal          : 2,13 V
  ohmR4sInternal           : 96,64 Ω
  ohmCalcR4                : 63,64 Ω
  ampGndBaseQ3             : 733,33 μA
  ampR23                   : 148,94 μA
  ampR5                    : 882,27 μA
  ohmR5sOnResistance       : 4,87 kΩ
  ohmCalcR5                : 4,87 kΩ
PROVIDES
  ohmR4                    : 68 Ω
  ohmR5                    : 4,7 kΩ

VIRTUAL GROUND TARGET VOLTAGE
NEEDS
  Empirical values TL082
NEEDED BY
  Triangle wave voltages
  Virtual ground en reference voltage dividers
CONSUMES
Empirical values TL082
  voltSwingToGroundNominal : 40,00 mV
  voltSwingToVCCNominal    : 3,70 V
PROVIDES
  voltNominalValue         : 1,87 V

TRIANGLE WAVE VOLTAGES
NEEDS
  Choosen values
  Empirical values TL082
  Virtual ground target voltage
NEEDED BY
  Virtual ground en reference voltage dividers
CONSUMES
Virtual ground target voltage
  voltNominalValue         : 1,87 V
Empirical values TL082
  voltSwingToGroundNominal : 40,00 mV
  voltSwingToVCCNominal    : 3,70 V
Choosen values
  ohmR6                    : 47,00 kΩ
  ohmR3                    : 100,00 kΩ
PROVIDES
  voltLow                  : 1,01 V
  voltHigh                 : 2,73 V

VIRTUAL GROUND EN REFERENCE VOLTAGE DIVIDERS
NEEDS
  Empirical values 1N4004
  Choosen values
  Virtual ground target voltage
  Triangle wave voltages
GOAL
Determine resistance values such that:
  VirtGnd can be set voltVirtualGroundMargin higher or lower than the determined one with RV3
  Voltage difference between RefLow - RefHigh can be set to 25% of the voltage difference between voltTriangleWaveLow and voltTriangleWaveHigh
  Voltage difference between RefLow - RefHigh can be set 10% higher than the voltage difference between voltTriangleWaveLow and voltTriangleWaveHigh
  The maximum settable voltSettableVirtGndLow should go as lease low as voltSettableVirtGndLowMax
  The minimal settable voltSettableVirtGndHigh should go at least as high as voltSettableVirtGndHighMin
  RV1 mid and RV3 mid should be optimized so that voltVirtGndCtrl matches voltVirtGndTarget
  Maximum current should be optimized to ampVirtGndVoltageDividerTarget
CONSUMES
Choosen values
  ampVirtGndVoltageDividerTarget: 7,00 mA
  voltVCC                  : 5,00 V
  ohmRV1                   : 1,00 kΩ
  ohmRV3                   : 500,00 Ω
  voltVirtualGroundMargin  : 250,00 mV
Empirical values 1N4004
  voltForwardVoltage       : 700,00 mV
Virtual ground target voltage
  voltVirtGndTarget        : 1,87 V
Triangle wave voltages
  voltTriangleWaveLow      : 1,01 V
  voltTriangleWaveHigh     : 2,73 V
INTERMEDIATE
  voltVCCMinusD3           : 4,30 V
  voltTriangleWaveDelta    : 1,72 V
  voltSettableReferenceDeltaLowMax: 430,05 mV
  voltSettableReferenceDeltaHighMin: 1,89 V
  voltSettableVirtGndLowMax: 1,62 V
  voltSettableVirtGndHighMin: 2,12 V
  voltSettableVirtGndLow   : 618,36 mV
  voltSettableVirtGndHigh  : 2,25 V
  voltSettableRefDeltaLow  : 408,01 mV
  voltSettableRefDeltaHigh : 1,91 V
  voltVirtGndMidDif        : 371,54 μV
  ampTotMaxDif             : 399,22 μA
  ampMaxAmp                : 7,40 mA
PROVIDES
  ohmR1                    : 56 Ω
  ohmR2                    : 1,8 kΩ
  ohmR12                   : 1,8 kΩ
  ohmR13                   : 56 Ω
  ohmR14                   : 470 Ω

COMPARATOR LATCHES
NEEDS
  Choosen values
  Datasheet values 2N7000
  Datasheet values LM339
GOAL
Determine resistance values such that:
  When BeamBreak signal is high the latch is always low
  When BeamBreak signal is low, a closed switch SW1 can set the latch high
  When the output of U3A is high it stays high unless switch SW1 is pushed and BeamBreak signal is low
  Maximum current should acceptable when switch is closed and Q2 is conducting
  Different voltages should have good spreading
CONSUMES
Choosen values
  voltVCC                  : 5,00 V
Datasheet values 2N7000
  ohmOnResistance          : 6,00 Ω
Datasheet values LM339
  voltLowlevelOutputVoltage: 150,00 mV
  OptimumDelta             : 3,33294702420633
PROVIDES
  ohmR15                   : 12 kΩ
  ohmR16                   : 27 kΩ
  ohmR17                   : 82 kΩ
  ohmR18                   : 33 kΩ
  ohmR20                   : 39 kΩ
  ohmR29                   : 12 kΩ
  ohmR28                   : 27 kΩ
  ohmR30                   : 82 kΩ
  ohmR27                   : 33 kΩ
  ohmR31                   : 39 kΩ


Yansi:
You seem you have had just too much fun building this circuit.

BTW, most IR opto-gates are made using a double modulation. First, there is a carrier frequency (usualy couple tens of kHz), so the light can be easily distinguished from a background noise and DC component of the ambient light completely canceled out at the sensor (just narrowband AC amplifiers/filters present). Then the carrier is OOK modulated at a couple of hundred Hz.

Transmit side can be implement by a pair of oscillators (for example a couple of 555 timers), the receive side is quite simple too, when using an off-the shelf IR receiver with integrated demodulator (those obligatory 36, 38, 56kHz  IR remote control receivers), the evaluating logic can then be made using a missing pulse detector and a pulse stretcher (which, quite funnily could be made also using a couple of 555 timers).  ;)
HendriXML:
Instead of reporting all tasks, it is also possible to zoom in on one and its required tasks.
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