You will need some sensors to get the most out of the controller so I will give a quick rundown on how to make a couple.

The first is a laser trip wire, this is a laser module which sends out a beam which bounces off a reflector back to the laser and is picked up by a photo transistor. The reflector is a retro reflector which basically means it bounces the light back in the opposite direction to which it arrives, this means you don’t have to spend the best part of a day trying to get the dam thing lined up – you just stick the reflector somewhere and aim the laser at it.

Another advantage of this approach is that the detector and laser are in one box, so there is only one cable to worry about, although its perfectly feasible to separate the detector and laser if you wish to point one directly at the other.

I have been messing about trying to get maximum range out of this for a few days and I came to the conclusion it was a waste of time because you are very unlikely to need a laser trip line longer than a couple of meters anyway, and this one will work up to at least 4 or 5 meters in bright daylight & considerably more in low light conditions.

If you only need a few meters distance (and you probably will) then you can just use retro reflective tape, the stuff you get from cycle shops that lights up really bright in car head lights and is often sewn on clothes etc. If that doesn’t give you enough distance then you can get a front cycle reflector, these white retro reflectors bounce a lot more light back and will extend the range quite significantly.

If you are still hungry for more, and you have the patience of a saint, you could always use a standard mirror to bounce the beam back. That would I guess give you well over 100m range if you ever manage to line up the mirror LOL

So what is the laser trip wire good for? Surprisingly enough its absolutely no use for tripping people up but it is very good for detecting moving objects. You could for instance set up the beam and drop objects through it and capture them in mid air, you could set it across a path where animals pass and get some wildlife pics without having to sit in the cold dark garden, aim it across a road and take photos of traffic :-S Well, I would guess there are plenty of uses for it if you put your mind to work..

It is fast as well, the reaction time of a photo transistor is way faster than a light dependent resistor which my first version used, this sensor will pick up my hand passing through the beam as fast as I possibly can without my hand departing company from my arm!

OK, enough babble I think, on with the making of..

There are only 3 components to it, the laser module, an SFH300-3 photo transistor , and a 120kΩ resistor (brown/red/yellow bands) Don’t come much easier than that! You will also need a box of some description to mount it in, a bit of 3 core cable, a 3.5mm stereo jack plug and a small piece of veroboard to mount the photo transistor & resistor on.

The box needs to be  about 150mm long but does not need to be much above 40 or 50mm wide & high, it also needs to be light tight – totally opaque. The reason being the laser module will be at one end pointing out, and the light bouncing back will go through a small hole next to the laser and hit the photo transistor at the other end of the box. This will eliminate most of the ambient light and make the sensor work in daylight.

A picture being worth a thousand words I could have just shown you the following picture instead of all that drivel

Controller Prototype

Wow check that out full size and imagine what I could come up with if I had at least one artistic bone in my body!

If you are wondering where you can get a box like that, maplin have one, or rather they have on the website but not in stock grrrr. It doesn’t have to be square though, so you could make one out of a piece of black waste pipe. Oh yeah, I forgot to mention its better to have a black box or at least line it with black gaffer tape or something to stop any stray light bouncing round inside it.

Any road up, the hole for the reflected light to go through needs to be right next to the laser module, in fact touching it is even better because the light is reflected straight back at the laser itself and is therefore brightest right next to it.

To find the position for the photo transistor first mount (glue) the laser into the end of the box so the beam comes out parallel to the box, then cut the little hole next to it about 5 or 6mm diameter. The box I used had slots for mounting circuit boards in so I cut a piece of veroboard to fit, you could just sticky pad it to the end of the box but first you will need a rough position for the photo transistor.

Power up the laser module, the ones I use are 5v so I just plugged it into +5v & ground on the arduino, and aim the laser at a retro reflector as detailed above positioned 2 or 3m away. If you dim the lights (turn them off) you will see a spot on the back of the box where the reflected laser light hits, that is where the photo transistor wants to be. If you intend to sticky pad the veroboard in place, first just hold it in position and mark the point where the light hits it, once you have mounted the components on the board you can repeat this procedure when sticking the board in place so the light hits the transistor.

Now you need to mount the components on the veroboard and solder them in place. When soldering the transistor to the board it is a good idea to hold the legs in a pair of long nose pliers between the board and the plastic head of the transistor to prevent the heat getting to the delicate part of it. Once soldered in place you can cut off the excess wire leg with wire cutters or nail clippers.

The transistor has to be connected the right way round with the short lead going to the +5v, if you have cut the leads and forgot which is which there is a flattened bit on the +5v leg near the plastic head. Likewise the laser module has to be connected the correct way round, the red wire being +5v and the black one ground.

They will be positioned on the veroboard as shown in the following picture.

Controller Prototype

The position for the components can be adjusted to suit where the light hits the board, but move them all together so the connections are all the same as the above picture.

Please note, this picture is viewing the coper strip side, the components and wires will be mounted on the other side with the legs poking through the holes and soldered to the copper strips. Pay particular attention to the short leg of the photo transistor which will come through the hole marked +5v above.

The resistor is shown in pink, the photo transistor in green.

When you solder the connections on the veroboard make sure you do not bridge the gap between the copper tracks with solder, to make sure run a Stanley knife blade up and down a few times between the copper tracks, even the slightest strand of solder between tracks can screw it up – yes, I found out the hard way grrrr.

Now you have everything soldered in place, power up the laser again and stick the board to the end of the box so that the head of the photo transistor is in the spot of reflected light, you need to be spot on with the position because if it is as much as a mm out it will reduce its effectiveness drastically.

The wire to jack plug is the 3 core cable used to connect the sensor to the controller, I just used a piece about 500mm long which passes through a hole in the end of the box after soldering to the board – tie a not in it to stop it pulling out of the box You can extend this lead with cheap headphone extension cables from the bay of E, a 10m extension can be picked up for less than a fiver

The 3 cores need soldering to a jack plug, the red one (+5v) goes to the tip of the jack plug, the blue one or your equivalent colour (signal) goes to the middle band, and the black one (ground) goes to the band next to the jack plug body.

Stick the lid on the box and you now have a cool laser trip wire detector for less than a tenner.

See how easy that was? Just as well really,  now you have finished you can do it all over again because the controller will then operate in directional and cross beam sensor modes – with the directional mode you can take photos only if the object is moving in a specific direction when it breaks the beam and with cross beam mode it will only take a picture when the object is at the exact point the two beams cross

Now for an optical switch or optical interrupter whichever you prefer.

This is a small unit with an infra red emitter and detector in a plastic package, the detector/ emitter are only about 8mm apart so it wont be much good for detecting passing elephants but it is rather good at detecting small things such as water drops.

With this sensor plugged into the controller and positioned under a dripping tap you can capture pictures of water splashes with the greatest of ease.

Now if you thought the laser trip wire was easy you will love this because it only has 2 components! There is an SX4070 optical switch and a 220Ω resistor (red/red/brown bands), this thing will fit into half a matchbox!

The best way to make this into a hardy little sensor is to cut a square hole in a small plastic moulding such as you get small products packed in, the plastic wrap usually fixed to a card backing. If you make the hole just big enough to poke the body of the interrupter through the exposed electronics will be inside the container which you can then fill with epoxy resin. Once set you can remove the plastic container and you are left with the interrupter with all the bits you don’t want to get wet encased in a nice resin block – completely water proof

Here is a pic of the veroboard, again this is viewing the copper track side and components & wires would be on the other side poking through the holes..

Controller Prototype

As you can see, it will fit on a piece of veroboard 3 copper strips wide by 8 holes long. When you come to making this board up you need to cut the 3 tracks where indicated, the easiest way to do this is to use a 6mm drill bit hand held to cut away the coper track – making sure the track is cut all the way across without any thin slivers of copper remaining at the edges.

The first thing you need to do is solder in a short piece of insulated wire as shown in yellow, then solder on the 220Ω resistor as shown in green. Remember the components and wires go on the plain side with the leads poking through the holes into the copper side.

Next solder a short length of 3 core cable to the top row of holes as shown, be careful not to block the next row of holes where the optical switch will be fitted.

The optical switch is then soldered in place OVER the resistor and wire jumper, the leads are long enough to allow you to solder it in place with the components under it. If you have a pair of long nose pliers grip each wire leg where it comes out of the plastic body as you solder it to the board to prevent any heat damage.

Once done cut any excess wire legs off using wire cutters or nail clippers and you should have a very compact sensor ready to encapsulate in epoxy resin.

When you encapsulate the back of it in resin, make sure the outer insulation of the cable is covered in resin so the cores wont get pulled from the cable. Also it may be advisable to add the resin in stages 2 or 3mm at a time, some epoxy resins will generate quite high temperatures when the chemical reaction sets in so to minimise this do it in a few stages allowing it to cool in between.

You could also embed a stiff wire loop in the last layer or two of resin to enable you to  position it in use if it takes your fancy

You should stick a 3.5mm jack plug on the end of the cable using the same connections as the laser sensor

Optical switch sensor, total cost 3 or 4 quid

I intend to include details of a sound activated sensor here as well but unfortunately I am still waiting for some of the components to be delivered so I will update this post when I get them and test the circuit out.

So that concludes this latest episode in the Great Camera Controller book, next up I will explain making up the circuit on a bread board so you can get it all up and running.

Tags: Arduino, DIY, Electronics, Photography

This entry was posted on Wednesday, November 4th, 2009 at 7:04 pm and is filed under Photography Tutorial. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.