Experimental Brightness Attenuator / Scan fail

[mixedgas]

OK, a while back one William R. Benner wanted to see whom could get the closest to a 69 cent scan fail. His requirement was one opamp, low cost parts, and easy to adjust.

Here is my latest entry.


Note, this is not a absolute scan fail, it is a simple design, and attenuates the laser instead of 100% switchoff. It will pull a 5V analog input to six tenths of a volt, in other words most lasers will not go 100% off. This could be improved by replacing Q2 with a N channel Fet.

Operation, it looks for large voltage swings in the galvo feedback signals, yet tends to ignore small, noisy, signals.

I'm still toying with it in the simulator, but some of you may find the input block "interesting" for conditioning analog signals.

The circuit is not "calibrated" for any given situation, that is up to the builder.
for example, the diode used to set the threshold may be switched to a potentiometer, and altering the resistor (R5) in front of the two coupling caps changes the input frequency response somewhat. You may of course replace the back to back caps with a "NPO" non polarized electrolytic.


One of these days I may try turning Q1 and Q2 into a monostable, but for now, its a nice toy in the simulation software.

Note, corrected attached drawing.

Steve

[dar303]

Nice, good job!
I don't have the time to try it for real but I hope someone else does it and reports back!

[mccarrot]

The schematic looks very clean, nice job.

Is it possible to add a horizon control with a potentiometer so you can have the scan fail on below the horizon and still can use static beams above the horizon.

[mixedgas]

The schematic looks very clean, nice job.

Is it possible to add a horizon control with a potentiometer so you can have the scan fail on below the horizon and still can use static beams above the horizon.

As that sort of defeats the purpose of "Bills challenge" I'm going to give that to you in a different format.

LT Spice is a free download and a breeze to use, although it has some limitations. You can even convert one axis of a ILDA file to a wav file using Laserboy, and import it as a waveform. Have not tried it that yet, I test things with 2 sine or square waves, plus noise, beat together in a mixer circuit and input into the DUT circuit. If the waves are audio and say 1.00 Khz and 1.020 Khz, you can get nice simulations for test.

LT SPICE DOWNLOAD:
http://www.linear.com/designtools/software/ltspice.jsp

While I could of just added a HC series logic gate, I kept with the M^2L spirit.
Note M^2L is "mickey mouse logic", logic done with crude yet effective, cheap, parts.
Use TL084 for the opamps and LM741 for the compare circuit.

Paste the following text into a text file called scanfail2.asc and copy it to the LT Spice directory.

Steve

Version 4
SHEET 1 1596 880
WIRE 1296 96 1280 96
WIRE 1328 96 1296 96
WIRE -352 112 -368 112
WIRE -256 112 -272 112
WIRE 1296 112 1296 96
WIRE 128 128 48 128
WIRE 288 144 192 144
WIRE 368 144 288 144
WIRE 128 160 96 160
WIRE -368 176 -368 112
WIRE 96 176 96 160
WIRE 608 176 576 176
WIRE 1024 176 1024 160
WIRE 1104 176 1088 176
WIRE 1104 192 1104 176
WIRE 1296 192 1200 192
WIRE -368 224 -368 176
WIRE -352 224 -368 224
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WIRE 1088 224 1024 224
WIRE 1200 224 1200 192
WIRE 1200 224 1184 224
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WIRE -256 240 -288 240
WIRE -160 240 -176 240
WIRE -80 240 -96 240
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WIRE 48 256 -16 256
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WIRE 288 256 288 208
WIRE 288 256 208 256
WIRE 448 256 448 144
WIRE 496 256 496 176
WIRE 496 256 448 256
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WIRE 608 272 608 176
WIRE 608 272 576 272
WIRE 640 272 608 272
WIRE 848 272 784 272
WIRE 960 272 928 272
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WIRE 1120 272 1088 272
WIRE 288 288 288 256
WIRE 512 288 496 288
WIRE -384 304 -384 256
WIRE 496 320 496 288
WIRE 784 320 784 272
WIRE 1200 320 1184 320
WIRE 48 336 48 256
WIRE 128 336 48 336
WIRE 704 336 704 272
WIRE 288 352 192 352
WIRE 368 352 288 352
WIRE 448 352 448 256
WIRE 128 368 80 368
WIRE 1024 400 1024 320
WIRE 784 416 784 384
WIRE 1200 416 1200 320
WIRE 704 448 704 416
WIRE -32 528 -32 512
WIRE 80 528 80 368
WIRE 80 528 -32 528
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WIRE 112 592 64 592
WIRE -32 624 -32 592
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WIRE -112 672 -112 656
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WIRE 64 672 -112 672
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WIRE 112 688 112 672
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WIRE 960 688 960 272
WIRE 960 688 736 688
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WIRE 384 704 320 704
WIRE -112 768 -112 736
WIRE 416 768 416 720
WIRE 512 768 512 688
WIRE 112 800 112 768
WIRE 320 832 320 704
WIRE 512 832 320 832
FLAG 96 176 0
FLAG 496 320 0
FLAG -384 304 0
FLAG -32 624 0
FLAG 1024 400 0
FLAG 704 448 0
FLAG 1200 416 0
FLAG 1104 192 0
FLAG 784 528 0
FLAG 416 768 0
FLAG 112 800 0
FLAG -112 768 0
SYMBOL Opamps\\LT1001 160 80 R0
WINDOW 3 236 -4 Left 0
SYMATTR InstName U1
SYMBOL Opamps\\LT1001 160 288 R0
WINDOW 3 233 -212 Left 0
SYMATTR InstName U2
SYMBOL Opamps\\LT1001 544 336 M180
WINDOW 3 -148 263 Left 0
SYMATTR InstName U3
SYMBOL res 224 240 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R1
SYMATTR Value 10K0
SYMBOL diode 272 144 R0
WINDOW 0 7 -48 Left 0
WINDOW 3 19 -19 Left 0
SYMATTR InstName D1
SYMATTR Value 1N914
SYMBOL diode 272 288 R0
WINDOW 0 33 -27 Left 0
WINDOW 3 20 104 Left 0
SYMATTR InstName D2
SYMATTR Value 1N914
SYMBOL res 464 128 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R2
SYMATTR Value 10K0
SYMBOL res 464 336 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R3
SYMATTR Value 10K0
SYMBOL res 480 160 M90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R4
SYMATTR Value 10K0
SYMBOL polcap -160 224 M90
WINDOW 0 0 32 VBottom 0
WINDOW 3 32 32 VTop 0
SYMATTR InstName C1
SYMATTR Value 22µ
SYMATTR Description Capacitor
SYMATTR Type cap
SYMATTR SpiceLine V=63 Irms=215m Rser=0.52 Lser=0 mfg="Nichicon" pn="UPL1J220MPH" type="Al electrolytic"
SYMBOL polcap -16 224 R90
WINDOW 0 0 32 VBottom 0
WINDOW 3 32 32 VTop 0
SYMATTR InstName C2
SYMATTR Value 22µ
SYMATTR Description Capacitor
SYMATTR Type cap
SYMATTR SpiceLine V=16 Irms=55m Rser=2.4 Lser=0 mfg="Nichicon" pn="UPR1C220MAH" type="Al electrolytic"
SYMBOL Opamps\\LT1001 -320 176 R0
WINDOW 3 766 -109 Left 0
SYMATTR InstName U4
SYMBOL res -160 224 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R5
SYMATTR Value 4k7
SYMBOL res -256 96 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R6
SYMATTR Value 1k
SYMBOL res -48 416 R0
SYMATTR InstName R7
SYMATTR Value 10K0
SYMBOL diode -48 528 R0
WINDOW 0 54 32 Left 0
SYMATTR InstName D3
SYMATTR Value 1N914
SYMBOL res -352 96 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R8
SYMATTR Value 1k
SYMBOL res -352 160 R90
WINDOW 0 -184 -132 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R9
SYMATTR Value 1k
SYMBOL diode 640 288 R270
WINDOW 0 32 32 VTop 0
WINDOW 3 0 32 VBottom 0
SYMATTR InstName D4
SYMATTR Value 1N914
SYMBOL res 800 256 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R10
SYMATTR Value 10K0
SYMBOL cap 768 320 R0
SYMATTR InstName C3
SYMATTR Value 1µ
SYMBOL res 944 256 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R15
SYMATTR Value 470
SYMBOL npn 960 224 R0
SYMATTR InstName Q1
SYMBOL npn 1120 224 R0
SYMATTR InstName Q2
SYMBOL res 1008 64 R0
WINDOW 3 -63 55 Left 0
SYMATTR Value 10K
SYMATTR InstName R11
SYMBOL res 688 320 R0
SYMATTR InstName R12
SYMATTR Value 10K
SYMBOL zener 1088 192 M270
WINDOW 0 36 32 VTop 0
WINDOW 3 -4 32 VBottom 0
SYMATTR InstName D5
SYMBOL res 1184 80 M90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R13
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SYMBOL res 1312 80 M90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R14
SYMATTR Value 100
SYMBOL res 1280 208 M180
WINDOW 0 36 76 Left 0
WINDOW 3 36 40 Left 0
SYMATTR InstName R16
SYMATTR Value 300
SYMBOL res 768 400 R0
SYMATTR InstName R17
SYMATTR Value opt
SYMBOL Opamps\\LT1001 416 624 R0
WINDOW 3 -1 -555 Left 0
SYMATTR InstName U5
SYMBOL diode 544 704 R270
WINDOW 0 32 32 VTop 0
WINDOW 3 0 32 VBottom 0
SYMATTR InstName D6
SYMATTR Value 1N914
SYMBOL res 96 576 R0
SYMATTR InstName R18
SYMATTR Value upper
SYMBOL res 96 672 R0
SYMATTR InstName R19
SYMATTR Value lower
SYMBOL zener -96 736 R180
WINDOW 0 24 72 Left 0
WINDOW 3 24 0 Left 0
SYMATTR InstName D7
SYMBOL res -128 560 R0
SYMATTR InstName R20
SYMATTR Value 1K
SYMBOL cap 496 768 R0
SYMATTR InstName C4
SYMATTR Value 100pf
SYMBOL res 320 512 R0
SYMATTR InstName R21
SYMATTR Value 1K
SYMBOL res 752 672 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R22
SYMATTR Value 470
TEXT -48 400 Left 0 ;Vcc
TEXT -512 112 Left 0 ;X IN
TEXT -520 176 Left 0 ;Y IN
TEXT 1128 24 Left 0 ;COLOR IN
TEXT 1432 72 Left 0 ;COLOR OUT
TEXT 1008 48 Left 0 ;VCC
TEXT 1272 16 Left 0 ;ATTENUATOR
TEXT 976 -16 Left 0 ;INVERTER
TEXT 560 80 Left 0 ;SCHMIDT
TEXT 72 56 Left 0 ;CONDITIONER
TEXT -336 32 Left 0 ;BUFFER
TEXT 88 416 Left 0 ;Threshold Voltage
TEXT 736 136 Left 0 ;TIME
TEXT 712 168 Left 0 ;CONSTANT
TEXT -168 104 Left 0 ;AC COUPLING
TEXT -128 536 Left 0 ;VCC
TEXT 408 576 Left 0 ;VCC
TEXT 248 480 Left 0 ;+Y IN (ZERO LINE)
TEXT 32 848 Left 0 ;Threshold Voltage
TEXT 296 864 Left 0 ;STATIC BEAM OVER RIDE

[mccarrot]

Thanks for sharing!!!

I never used this program, so I'm a little bit in a learning curve at the moment, learning how to do good simulations.

I'm more used to breadboards and a scope.

[mixedgas]

Thanks for sharing!!!

I never used this program, so I'm a little bit in a learning curve at the moment, learning how to do good simulations.

I'm more used to breadboards and a scope.

Yeah, the sim mode learning curve is steep, and the fact that the default parts are mostly all Linear Tech chips can be a bit of a drag. It has trouble with a few minor things like linear oscillator circuit startup, but its free,has many users, is actually pretty good, and you can reach the guy who writes it if you have issues.

Compared with other spice programs on the market, it is easier to use, in my opinion.

I too do bench models, but when I need to bang out a analog circuit for someone who can already solder, owns a scope, and can decode parts packages and pinouts, it rocks.

So I figured you'd like to do a little learning.

Steve

[flecom]

see I never understood the point of one of these scan fails... if you have a beam stop to prevent your projection from entering the audience it seems like one extra thing that can go wrong in your show...

plus sometimes a slow, sweeping static dot can be a really cool effect for certain songs... although pangolin usually inserts invisible "points" even if your just projecting a dot so maybe it won't be an issue

[norty303]

Guidelines for crowd scanning 10xMPE are that you have a suitable scan fail device in operation

[flecom]

Guidelines for crowd scanning 10xMPE are that you have a suitable scan fail device in operation

ya for you maybe, over here doing audience scanning legally isn't worth the trouble/resulting effect

[mccarrot]

see I never understood the point of one of these scan fails... if you have a beam stop to prevent your projection from entering the audience it seems like one extra thing that can go wrong in your show...

Now what if your galvo PSU breaks down.

Or one of the galvo's gets a melt down and get stuck (sometimes seen with chinese scanners)

Or some idiot drive over your ILDA cable shorting only the X Y wires

Or one of the Galvo drivers dies

Or one of the galvo cable comes loose due to the 10KW PA system next to the laser.

Or one of the galvo bearings gets stuk

or.....

or...

or....


I hope the scanfail will never have to do its job, but if something goes wrong you will be happy you have it.

Also if there is problem where a audiance member gives you a claim its good to proof you have a scanfail in place, this give you a advantage in court...

finaly the guidelines advise you to use a scanfail.



On only time you do not need to use a scanfail is when you mask of the audiance area with a cover, so in case of a problem there is zero chance a beam hits the audiance.