Laser trip wire

I am thinking about building some more sensors for my high speed photography unit. there going to be some requirements that I haven't quite figured out as yet to do with using multiple sensor and alike.
The first task was to get an idea about what I need, and the best way to go about it. the idea at the moment stands at using a 14m2 to handle any of the future comms (maybe single wire serial, to controller and the same again to other sensors) that I am going to need and to produce a 38khz pwm to control the a laser (yes I know lasers are dangerous). from there I thought about a narrow pass filter would do the job, however using the attached PDF I found that things got tricky quickly with resistor sizes. As a result I am now left wondering if LED020 will be able to handle a few milliwatt (1-3mW would be enough) laser as it already has the appropriate filter built in? Will it handle having the laser on continuously?

The laser will need to be able to be switched off when the system fires. normally I would think that running the PWM through the base of a transistor would be enough, should I use 2 transistor, the first producing the PWM, and the a second being an "on/off" switch? or something else altogether?

any suggestion about transistors and lasers are welcome, I only BC548 Transistors here at the moment so will need to order more. most basic lasers out there seem to be around the 40mA mark so the picaxe wont be able to supply the juice it needs.

this is primarily going to be for capturing insect to flower or some sort of "bait" so will need to function during the day and a normal wide angle IR beam most likely wont work.

A few quick stream of consciousness thoughts.


http://www.picaxeforum.co.uk/showthread.php?13033-Flash-Camera-Trigger-Thing&highlight=Laser



http://www.picaxeforum.co.uk/showthread.php?12786-Lasers-and-sticky-tape&highlight=lasers



And cheap LASER pointers as the source,
using the highest value resistor possible,
then adding BPW34 detectors.



Plenty more info on the Forum.
e

Red laser~630-680nm
IR receiver module ~940 nm peak sensitivity

Might work at close range from sheer intensity, but far from an ideal match.

Have you played with Hamamatsu's S6986 sensor, as Philo used with a red laser & reflector? I had very good results.

http://www.philohome.com/sensors/lasersensor.htm

your lazer tripwire reminded me of this example

http://afrotechmods.com/tutorials/2011/11/28/photoresistor-tutorial-laser-tripwire-circuit/


tony

laser pointer could be source of lasers, however I was thinking of http://www.ebay.co.uk/itm/650nm-6mm-5V-3V-5mW-Red-Laser-Dot-Diode-Module-Copper-Head-/111686641465?var=&hash=item1a010ae739:m:mcdbXKwlve-mfYFFsUO0QMw

the BPW34 looks good, I could be easily combined with a 640nm optical filter to only allow the laser wave length through
the S6986 will need a closer look, as I would ideally be able to use it with or without a mirror the TX and RX unit need to in separate units. I will also need to look into if the while unit will need to be switched off, or just the laser section (Don't suppose its going to make a big difference).

I need to have a look and see if I will need any optics inform of the receiver as well
I have found some thing similar on the market to give you a better idea of the sort of system that I am looking at trying to build.
http://gizmodo.com/5995394/this-laser-shutter-photography-rig-freezes-insects-in-flight
https://www.cognisys-inc.com/how-to/stopshot/xbs.php

Edit: S6986 seems tricky to get hold of. seems that its only available in bulk

oracacle said:

laser pointer could be source of lasers, however I was thinking of http://www.ebay.co.uk/itm/650nm-6mm-5V-3V-5mW-Red-Laser-Dot-Diode-Module-Copper-Head-/111686641465?var=&hash=item1a010ae739:m:mcdbXKwlve-mfYFFsUO0QMw

the BPW34 looks good, I could be easily combined with a 640nm optical filter to only allow the laser wave length through
the S6986 will need a closer look, as I would ideally be able to use it with or without a mirror the TX and RX unit need to in separate units. I will also need to look into if the while unit will need to be switched off, or just the laser section (Don't suppose its going to make a big difference).

I need to have a look and see if I will need any optics inform of the receiver as well
I have found some thing similar on the market to give you a better idea of the sort of system that I am looking at trying to build.
http://gizmodo.com/5995394/this-laser-shutter-photography-rig-freezes-insects-in-flight
https://www.cognisys-inc.com/how-to/stopshot/xbs.php

Click to expand...

looking at the commercial product it looks awfully like a load of plumbing, it's not much help but it did occur to me that 20mm (ish) PVC plumbers pipe has load's of TEE's and elbows as standard that would be quite good for a prototype I expect changing ambient light levels could be problematic therefore a pulsed light beam may be the easiest to reliable detect, a phase lock loop type tone detector chip could be used. The focus of the IR/laser receiver will need to be quite narrow if small insects are to be detected the simplest solution without getting into using lenses is a long narrow black tube, I have used old felt tip pen tubes in the past just to narrow the viewing angle, it reduces sensitivity but from what I saw of the commercial product the distances are quite small and the main issue may actually reducing the amount of light detected because there may be some scatter that the receiver may detect when the beam is broken. There are plenty of cheap laser pointer type diodes on the likes of e-bay many have a handy lens mounted in the front to focus the beam even if you do not use them in the detection system they are very handy for aligning the system and pointing out where the target area is. Not much help from the programming angle I'm afraid but it's my three penny's worth.

its the hardware I am working on the moment, the problem with the pulsed laser which is normally termed as a carrier frequency is what I causing the issue. if you have 650nm laser with a 38khz carrier you than need to have a band pass filter (for 38khz) on the receiver side so that only signals of the frequency are allow to the circuitry beyond. this is why the S6986 is ideal due to the fact that it both produces the carrier and filters for it and a single package.

I may order some optical filters and some standard photo diodes (the ones from rev ed maybe) and see if I can get good enough detection without a carrier signal.
the reason for choosing laser over normal IR is for the small size of the detection area, a standard LED020 mentioned earlier would be fine for a detector if a standard IR LED with the same 920nm wave length was being use.
if I could find laser with a 920nm wave length then that the plan I would use.

oracacle said:

S6986 seems tricky to get hold of. seems that its only available in bulk

Click to expand...

Very true, I bought a bunch direct from Hamamatsu, still have some, $7.50 each plus shipping. I used to get them at http://www.junun.org/MarkIII/Store.jsp but it says backordered. If you buy some from me, I'll become an international distributor.

Also have tons of those Ebay laser diodes and plenty of nice reflective material, which I used in this Picaxe laser tracker:


and also in my Terminator robot: https://www.youtube.com/watch?v=dZTfIyrRne0

that's a nice offer erco, I will keep that in my option folder.
however I have just been going over the sums again, turns out I made a great a error.
I did
1/(2*pi*c1*freq)
should have been
1/2*pi*c1*freq)

as a result the resistor values now look a little more possible, with a C1 of 0.01uf I get r1 of 596.9, r3 11341.1 and r2 31.4
as these resistor values don't seem to exist I will have to find some that are close and re-arrange the formula (I am going to get help this, my maths is quite poor) to make sure that any filter that I make will work, or so I know what frequency to produce.
any ideas on which op-amp to use if I go this route?
it may be cheaper going this route than getting some S6986 from you erco

Not to try to pull you in a different direction, but are you considering how difficult it will be to get a tiny insect to put his hand in that laser beam?

yes I am considering that, a lure of some type - it will take some experimenting when time comes (I know summer is a little way off which will be when insect are about).
This will be able to be used for more than just insect, other larger animals, projectiles, vehicles maybe even water drops.
Part of the reason for at 2 sensors is that they can be set in a cross pattern so the camera will only fire when that are in the exact spot. the 2 sensor could also be used for timing (when connected to my recently completed timer) and then calculation of speed.
this I going to be part of a larger development idea I have for the high speed unit. the new unit will include a timer, maybe an FPU for running more complex mathematics of EV, time laps and HDR. the original unit is going to be the test bed for new sensors and programme ideas with new hardware being designed when I am happy with the sensors.

I have all winter to get most of the hardware and software sorted. so the when insect and bird start appearing things will be ready

Well I have done a little work before bed, I think I have rearranged the formula correctly on all counts. I haven't looked at which exact resistors are available but with a few assumptions on size its looking like I will be able to get between 38.19khz and 38.7khz through the filter.

any thoughts on which op amp to use. the PDF suggests I need 40dp of head room and gives the q= gain = r3+r4/2*r1 = 189486.305. I have no idea what this means in terms of a filter being used for this purpose, but I guess its more for audio application.

oracacle said:

that's a nice offer erco, I will keep that in my option folder.

it may be cheaper going this route than getting some S6986 from you erco

Click to expand...

BTW there is no shortage of sellers on Alibaba for cheap "S6986 sensors", but they are never the right parts. http://www.aliexpress.com/wholesale?catId=0&initiative_id=SB_20151023141225&SearchText=Hamamatsu+s6986

I have ordered from 3 different sellers and they always send the wrong part. Something clear with 3 leads (should be 4), or something with 4 leads but it's black (should be clear). The Alibaba sellers clearly have no idea what they are selling, which made me to go directly to Hamamatsu.

Erco is sending some sensors and reflective material. laser are on the way too.
I have turned my thoughts to how each of the sensors are controlled before I order any more. currently thinking about using a 08M2 in each unit to control the laser being on or off. The 08m2 will also receive serial instruction for the controller later in the project, but it also need to be able to check for other sensors and report that back to the controller so that a detection sequence can be set.
it would be nice to be able to control a large number of sensors but 2 is the current target.
As you can see there is only one communication wire which will make things interesting on that front.
at the minute the idea is to be able to set the system so it will only fire if all the sensors are activated, or in an order (simplest would be a cascade front to back or back to front if arrange in a linear order) or finally if any sensor detects something.
The last one could actually be done without issue as the controller has 2 sensor input using the comparator. the comparator is used as analogue sensors are used sometimes.

while part of my thinks that the 08m2 should be fine and can be clocked to 32mhz I am not sure how I am going be able to handle the large variance of the sensor activation, specially while keeping things reasonably quick. but these problems will be face not matter what PICAXE I use but some speed issues can be negated with faster clocks available on other parts.

You might get away with a single laser & sensor solution if you can use mirrors to create a grid of appropriate resolution. A sketch of one simple layout is attached, there are many others. Alignment is critical, so you would want to mount your mirrors and laser in a rigid frame. You could defocus the laser a bit to reduce the alignment sensitivity. Again, I was getting good signal detection from Scotchlite reflectors from 10-12 feet away (round trip distance 20-24 feet), so with good mirrors you should be able to bounce a beam around for a while for decent coverage.

On my laser tracker, I used just one sensor but multiplexed its output signal through 4 lasers so I would know which laser(s) were not being received. I don't think that info is necessary in your case. Seems like you have several options.

yes I can use that I certain events, however for small things such as insects the requirements for the lens means that there will be a very small area that the image can be successfully captured. the depth of field in some case can be less than a sheet of paper, although should never be the case in this setup. then there is the fact that the lens only has a certain field of view comes into play. so 2 laser in a cross formation, with the centre of the cross being the ideal location to fire the camera - this would need the "and" of both sensors. running through each could be for priming a camera trap in wildlife photography and "or" function for monitoring a trail where an animal could approach from 2 directions.

as I progress through this project I was intending to return to the chronograph project that I had difficulties with earlier in the year. the laser in you your set up could work quite well as a ballistic screen providing the response to of the sensor is fast enough. the high speed timer I recently completed based on hippys' timer can be used for initial testing. but the primary reason I built that was to be able to check things on the new controller when I start building it, fingers crossed it will have its own timer, not as accurate but hopefully good enough too allow the capture and calculate speed of projectiles and then go on to work out the amount of timer to arrival and when to fire the camera.

the current controller was never intended to be the final project, its a test bed for new sensors and new ideas that will be incorporated into the final thing. nut as it stands its quite a good piece of kit to have.
http://www.picaxeforum.co.uk/showthread.php?26768-High-speed-photography
hardware is unchanged, but there have been some software changes to add in some basic timer functions for shutter delay, long exposure and a couple extra camera functions.

erco, your diagram reminded me of the mirror I got out of my old useless laser scanner. Long, skinny and accurately made. All you would need is the rigid frame.

erco said:

You might get away with a single laser & sensor solution if you can use mirrors to create a grid of appropriate resolution. A sketch of one simple layout is attached, there are many others. Alignment is critical, so you would want to mount your mirrors and laser in a rigid frame.

Click to expand...