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I Spy With My Little Eye “Necessity is the mother of invention”, so the proverb goes. OK, so this little project isn’t quite an invention. But it was born of necessity. A few weeks ago, I had to install some burglar alarm wiring deep within a brick cavity wall. The architraves and door jambs were not yet fitted, so I had quite good access to the cavity. But the view inside the cavity was well and truly hidden by a bunch of power cables. I tried all the usual tricks of “fishing” for the alarm cable – yellow tongue, thin dowel, a telescopic wand, straightened-out coathanger – but nothing worked. Not only were the power cables completely blocking my view, I was at least a little wary of a power outlet one of them connected to (especially when poking around with the coathanger!). “If only I could see inside the wall…” It was about this time that I remembered seeing not one but many advertisements for small, relatively cheap TV cameras. Could I use one of these to be my eyes inside the cavity? If so, how? I wanted to know more about these cameras. They are available from many SILICON CHIP advertisers, with a range of prices as wide as the range of models and types. You can get colour or black By Ross Tester & white, various shapes and sizes, with various lenses and various resolutions, or quality. Most of the cameras, though, would be too big for this application. The majority are built into relatively small metal cases, usually around 32 x 32 x 20mm. Given that the average wall cavity is only about 25-35mm wide, these would either be a very tight fit – or no fit. Then there are the “micro bullet” cameras – longer but certainly thinner – mostly around 22mm diameter and about 60mm or so long. Now these were starting to look interesting! Of course, we’d need to come up with some type of mounting arrangement so as to get the camera right into the thick of the action, where it was needed. We were just about to order one of these bullet cameras when we spotted what appeared to be an even better choice. Along with the rest of their range of cased video cameras, Oatley Electronics were advertising a 380 TV line “Super Micro” CCD camera module – no case, just the module. The camera we selected is a “Super Micro B/W” from Oatley Electronics and it is micro – just 17mm wide, 16.5mm deep and 60mm long! At right is a front-on view of the same camera. We take advantage of the two bosses (on each side of the camera) to not only hold the unit in place in the slots cut in the conduit but also to mount the two infrared LEDs. 38  Silicon Chip Pic to come While not waterproof or apparently as robust as the micro bullets, they were smaller – 17mm wide and about 22mm across. And there was another advantage – their power supply was a lot less demanding – they’d work from about 9.5V to 14.5V where most of the other cameras needed a regulated 12V supply. The price was attractive, too: less than $100. While not available in colour, we reasoned that colour would be a luxury we could do without. Besides, we planned some form of infrared illumination so colour would be meaningless. So that was the camera we decided to go with. Now we could turn our attention to the “probe”. Initially, we planned to put the camera inside a length of PVC electrical conduit. The conduit would give rigidity but also (importantly, we believed) give very good insulation just in case the end came in contact with live wiring inside the wall cavity. An example: the back of power outlets and light switches are not covered and they usually have at least some live “bits” (screws, etc) which might be contacted. Admittedly, contacting them was fairly remote but we believed even a remote possibility should be eliminated. Out first prototype was made using a length of UPVC conduit. And while it worked most of the time, we found a problem in operation. If we struck an obstacle within the cavity (eg, those damn power cables!) we could “jiggle” the conduit around but we couldn’t twist it out of the way. What we needed was the ability to create a small bend in the end of the conduit “on demand” – most of the time it should be straight but if Searching inside a pitchblack cavity for an elusive cable is never easy. Our spy camera puts the odds way back in your favour. The very bright spot on the monitor is a timber joist right in front of the camera, illuminated by the two infrared LEDs fitted to it. Looking inside the cavity it was still pitch black – but the camera responds very well to infrared light. obstacles were struck, a bend would allow it to be twisted out of the way. How do you create a tight bend in PVC conduit? You cannot, of course – unless you use flexible conduit. But this normally would not be practical because it is too flexible. It also tends to coil because that’s the way it is supplied. To solve this problem, we used a combination of both standard and flexible PVC conduit, one telescoping inside another two. By trial and error, we ended up with a 0.5m length of 25mm flexible conduit, a 3m length of rigid 16mm PVC conduit and a 1m length of rigid 20mm PVC conduit. The third length of conduit was used to allow the slack in the cable to be taken up – but more on this shortly. Most of the time the rigid conduit slides almost all the way up the inside of the flexible conduit, effectively There’s not much required in the way of circuitry – most of what you need is already in the camera module. The camera can be run from a 12V battery for “away from power” operation (assuming you had a battery monitor) and the regulator circuit eliminated but we would still retain reverse-polarity protection diode D1 – just in case. October 2000  39 straightening it out. But if a bend is needed, some of the rigid conduit is withdrawn from the flexible, which can then curl. Originally we used a pin through both conduits to stop the flexible length sliding right off (it would be nasty to lose it – and the camera – inside the cavity!). We drilled holes for this pin every 100mm (up to the 500mm length of the flexible conduit) so that the amount of bend could be set as required. With the two conduits separated most of the way, the conduit bent more than 90°. With the two telescoped all the way in, the bend was minimal – no more than a degree or two. Having made the prototype this way, we now have an even easier method of controlling the bend and also preventing the flexible conduit sliding off. This involves the third length of conduit, the “handle” we mentioned before. By fastening the flexible conduit and the “handle” together with a suitable length of cord (eg, venetian blind cord) the two conduits would slide along the inner conduit as one, not only setting the amount of bend but ensuring the flexible conduit remained captive. is required, or even better, a small 1W type (if you can find one). We’ll show how we arranged the LEDs shortly. Illumination Power We mentioned before our plans to provide illumination. Because we are interested in the immediate area of the camera, only a small amount of illumination is required. We used two infrared LEDs in series which were powered from the same 12V supply as the camera, via a suitable resistor. These are run pretty hard to get the most light output. The current is limited by the 180Ω resistor to about 50mA, the maximum forward current of the infrared LEDs. With this, the level of illumination was more than adequate. In fact, it was great for the purpose! The only minor dilemma is the dissipation of the resistor – at 50mA, it’s about 0.35W so a 1/4-watt resistor (which are pretty standard these days) simply isn’t enough. A 1/2W resistor One of the features that attracted us to this particular camera (apart from size) was that it is quite forgiving when it comes to the power supply. It could handle from 9V to 14.5V DC. Most of these small cameras, especially the colour ones, demand a regulated 12V supply (in fact, you’ll void the warranty on some if you don’t use a regulated supply). So theoretically, we could run the camera from, say, a 9V plugpack. Why not a 12V plugpack? Off load, most 12V plugpacks deliver more than 12V – often alarmingly more. You may recall an article we presented in SILICON CHIP in December 1998 on how to regulate a 12V plugpack for this very reason. In that article, we pointed out that a typical 12V 1A plugpack delivers from 15-18V on light loads. It’s only when you start to draw near the rated current that the voltage becomes close to the rated output. So that would rule out a 12V plugpack because the maximum camera supply is 14.5V. Or would it? Why not do what we did in that previous article and add a 12V regulator. For the sake of a couple of dollars, we could ensure a 12V supply regardless of what ills the plugpack tried to hit the camera with. Into the bargain, we would remove (or at least minimise) the hum and noise which is typical of most plug-packs – resulting in a much clea-ner picture. This photo shows how we connected the two infrared diodes to the camera PC board (via a 180Ω resistor), at the point where + and – power comes in via a 3-pin plug on the other side. They were held in place with a dab of super glue. 40  Silicon Chip The drawing above and the photographs alongside show how the cavity camera was assembled. Of course there are other ways to do the same job – you may come up with even better ideas! One real “tricky” bit in this assembly was lining up the Veroboard to get the bolt through the hole. Perserverance pays off... So that is exactly what we did: made up a small regulator using a 7812 3-terminal regulator and an electrolytic capacitor. The value of the capacitor isn’t important – just as large as you can get into the conduit. 16mm conduit has an internal diameter of about 12mm and then we had to get the cable past. We found a 470µF, 25V capacitor which just fitted nicely. You might have to have a good search of your junkbox or do the rounds of the lolly shops to find a suitable electro. Of course, the whole power supply/ regulator could be eliminated if you wanted to run the camera from a 12V battery (and you also had a 12V monitor). Cable At one stage, we were planning to use thin 75Ω coax cable to run the camera to the monitor. Then we were going to run the 12V supply up the same coax, suitably isolated at both ends, of course. (This technique is used in just about every masthead amplifier installation, so we weren’t re-inventing any wheels). But then we discovered some very thin, very flexible shielded twin cable. Intended for audio applications, it has two individual insulated conductors surrounded by shield braid. It had two big advantages: each of the inner con- ductors were multi-strand, meaning it could be flexed a lot without damage. And it was significantly thinner than even the thinnest coax cable commonly available. (Yes, you can get ultra-thin 75Ω coax, around 1mm in diameter. Trouble is, you can only get it at specialist suppliers and then only in 400m rolls. And it ain’t cheap!) So instead of having to provide extra comAnd finally it’s finished with the addition ponents (RF chokes and of our proprietary “cotanger” hook. capacitors) to isolate the wasn’t even intended for video use. supply on the coax, we That means there would almost cercould run video in one of the conductainly be an impedance mismatch tors and power in the other. Simple, with both signal loss and unwanted convenient! The cable, by the way, reflections. But what the heck, we came from Jaycar Electronics and sells were only looking at a couple of mefor only 77c per metre (Cat. WB-1504). tres or so . . . and just about every video Of course, the shielded cable we cassette recorder user knows that you were considering wasn’t 75Ω; it October 2000  41 Parts List 1 AR-717R “Super Micro B/W” Camera Module (Oatley Electronics) 1 3m length 16mm UPVC electrical conduit 1 1m length 20mm UPVC electrical conduit 1 500mm length 25mm UPVC flexible electrical conduit 1 20mm PVC conduit end cap 1 20mm length 20mm UPVC electrical conduit 1 piece of Veroboard or similar, approx 12mm x 20mm 1 30mm heatshrink tube, approx 50-100mm long 1 RCA socket, chassis-mounting type (ie nut fastened) 1 2.1mm DC socket, chassis mounting (Jaycar Cat PS-0518 or similar) 1 small cable tie 3m twin shielded thin mulitstrand cable (Jaycar Cat WB-1504 or similar) 3m thin cord (eg, Venetian Blind cord) 1 wire hook, fashioned from heavy wire 1 30mm x 3/16in (approx) bolt, nut and washer(s) Semiconductors 1 7812 12V positive regulator 1 1A silicon diode (1N4001 or similar) 2 infrared 5mm LEDs Capacitors 1 470µF (or 1000µF) 25VW electrolytic capacitor 1 0.1µF capacitor, small (type unimportant) Resistors 1 180Ω resistor, 0.5W or small 1W (brown-grey-brown-x) can use ordinary figure-8 shielded for short distances. So why not? We gave it a go and voila! It worked perfectly. If there was signal loss or degradation, we couldn’t see it and, considering what we were going to use the system for, it didn’t really matter if there was. The monitor Here’s where many people might think they are going to come unstuck. But fear not! The output of the camera is standard composite video, 1V peak-peak. You’re going to need a monitor (mono or colour) which accepts this composite video. It cannot be fed into the antenna input because it’s not RF, á lá an off-air signal. Before you think “stymied” the vast majority of modern TV sets have video inputs. It’s often called an “AV” input. Yes, it is a bit inconvenient to lug around a 34cm TV set but it’s a price you might have to pay if you don’t want to invest in something smaller. As a matter of interest, we used a 14-inch Commodore computer video monitor which we rescued from a recent council cleanup. These monitors, originally used on Amiga computers, have a composite video input. Total cost? $0.00! What other options are there? If you want the smallest and lightest monitor possible, have a look at the range of tiny tellies at your local electronics or specialist video store. For example, Dick Smith Electronics has a couple of 10cm and 25cm colour TVs with A/V inputs which would be ideal. And when you’re not using it with the camera, you can watch TV! Another alternative would be a B&W security monitor. Jaycar Electronics have available two b&w monitors under $200 which would also be perfect. One is a 6" model and sells for only $123.54 while the larger 10" model is $190.58. Obviously, we haven’t tried these out but cannot think of any reason why they – or any other monitor which takes a standard composite video input – wouldn’t work perfectly. If you really needed to use a TV set without video input, you could always add a VHF or UHF modulator and then you could go in via the aerial socket on any TV set. Oatley Electronics have available a high quality linear modulator which suits this camera perfectly and gives an excellent picture on even el-cheapo TV sets (not always easy!). As a special favour to SILICON CHIP readers, Oatley Electronics will give you one of these modulators (yes give you one, totally free) when you purchase the video camera, just as long as you ask for it at the time of purchase. Some suitable monitors from Jaycar and Dick Smith Electronics These monitors and TVs have not been tried but should work perfectly with this camera. 6-inch b&w switching monitor from Jaycar, Cat QM3402, sells for $123.54 42  Silicon Chip 10-inch b&w security monitor from Jaycar, Cat QM3402, sells for $190.58 25cm 12/240V colour TV with A/V input from DSE, Cat G7230, sells for $460 10cm AC/DC colour LCD TV with A/V input from DSE, Cat G7240, sells for $368 Now that’s not a bad deal at all! So the options for monitors are much wider than you might imagine. It all depends on what you want, what you may currently have (or scrounge) or whether you need to buy something new. Construction The first step is to fit the two infrared LEDs to the camera. We soldered the LEDs together in series then secured them to the camera body with a couple of drops of super glue. The 180Ω resistor was soldered direct to the back of the camera PC board, immediately under the 3-pin connector. The other end was soldered to the anode of one of the series LEDs. The negative connection was made with a short length of flexible hookup wire, again soldered to the back of the PC board at the negative power connector and to the cathode of the other LED. The pads to which you solder the resistor and wire are pretty small, so you’re going to need a fine-pointed iron and a steady hand. It helps if you work under a magnifying lamp. To connect the camera to the outside world, a tiny three-lead plug connects to a socket on the PC board (the same socket we just soldered to on the other side of the board). The blue lead is a common ground for both power and video. The red lead is the positive power lead and the yellow the video output. We were a bit concerned about the fragility of this plug and socket system so made up a small connection board from a scrap of Veroboard. The whole point was to minimise any stresses on the leads to the camera, or the socket. The shielded cable was anchored to the Veroboard with a tiny cable clamp – the smallest we could find. As we said before, we housed the camera inside a short (500mm) length of 25mm flexible electrical conduit, into which telescoped a 2m length of 16mm PVC electrical conduit. The camera mounted just a little back from the end of the conduit, mainly to avoid damage to the lens. The way we mounted it was a little different: all we did was cut 30mm long slots in both sides of the end of the flexible conduit with a small angle grinder and slid the camera assembly inside, LEDs and all. The LEDs ended up sitting in the slots immediately in front of the camera bosses (see photo). The position of the LEDs was chosen carefully to be just behind the lens, thereby avoiding any light scatter. When we were satisfied with the position, the whole lot was sealed in place with some heatshrink tubing which locked it up tight. Of course, the heat applied was just enough to shrink the tubing: we didn’t want to risk damaging the camera. By the way, we obtained the length of flexible conduit from a local sparkie – in fact, it was on the rubbish pile on a building site. If this source isn’t available, you can buy flexible conduit by the metre at most electrical wholesalers. Likewise, the 16mm and 20mm conduit can be obtained from the same source (or, in fact, virtually any hardware store). When the inner conduit is tele­scop­ ed in as far as it can go, the flexible conduit is almost straightened out, so the camera points straight ahead. But if it is slid out by, say, 200-300mm, the natural curl of the flexible conduit takes over and the camera points in that direction. Rotating the conduit points the assembly, camera included, in a different direction. Naturally, when you rotate the conduit and the camera rotates, the picture also rotates. This can be a little disconcerting at first – by far the easiest way to “get your bearings” is to rotate the monitor by the same amount. Here’s where having a small monitor is a real blessing! We were concerned that the inner conduit might be jammed up against the camera board, causing damage, if it was telescoped too far into the flexible conduit. So we made a “stop” out of a short length of 20mm conduit (again, a scrap from a sparkie) which we secured inside the flexible conduit with a nut and bolt through the whole thing. This bolt also provided a mounting point for our wire hook which we fixed to the end of the conduit to help capture the wayward cables inside the wall (which, after all, is the whole purpose of the exercise). The diagrams explain how we put all this together; naturally you may choose to do it differently. Our hook was made with a piece of extremely difficult-to-obtain proprietary wire called “cotanger” (we may not have spelt that quite right), bent to an appropriate shape. (We used to see October 2000  43 old Valiants driving around with this wire used as a radio antenna but even this has gone out of fashion now...) By the way, the 20mm “stop” doesn’t really want to fit inside the flexible conduit. We overcame this by heating the flexible conduit with a heat gun (very carefully) so that we softened the PVC just enough to force the short length in. We did notice some degradation of the plastic at this point; perhaps you might like to make a smaller stop (say from a piece of dowel) and drill a hole through it for the wires to pass through. At the “user” end, we slid another 1m length of 20mm PVC conduit over the top of the 16mm conduit. The reason for this is threefold: (a) it gives a more rigid “handle” with which to control the camera; (b) it allows us to place power and video connectors inside; and (c) perhaps most importantly, this controls where the flexible conduit at the other end sits on the inner conduit. Sliding the handle all the way on allows the flexible conduit to slide nearly all the way off, thus bending. Sliding the handle back, almost all the way off, pulls the flexible conduit back on to the inner conduit, thus straightening it up. As we mentioned before, something we didn’t do (and now regret) was connecting both sliding conduits together with a length of thin cord. This would stop either coming right off the inner conduit; it would also prevent the connecting cable being stressed or broken. We would recommend fitting such a cable, as shown in the diagram. You might find the 16mm conduit a very tight fit inside the 20mm conduit – it depends a lot on brand. We had this problem but easily overcame it by giving the end of 16mm conduit a good rubdown with some gritty glass paper (about a grade 60 or so works well). Power and video connection A 2.5m length of the twin shielded cable connects the “camera end” to the “user end” of the conduit. At the “user end”, we terminated the cables in two ways. The positive (red) wire went to the output of the regulator. Its input was wired to a 2.1mm DC socket which fitted – just – inside the 20mm conduit “handle” we mentioned previously. The other wire (white) was 44  Silicon Chip soldered to a standard RCA socket for the video connections. This socket didn’t fit inside the conduit so we placed an end cap over the 20mm conduit and fitted the socket in that. Naturally, the common earth (braid) was wired to both the DC socket and the video socket. The braid was in fact looped through the hole in the regulator tab, then soldered to the tab itself (which is also a “common” or ground connection). Our old Commodore monitor cost us nothing but is This means that the still great for use with this camera. The photo doesn’t majority of the stress do the image on the screen justice but it was of a on the cable is on the virtually pitch black cavity illuminated adequately by braid, which is the the two infrared LEDs. strongest part of it. We marked its position on the end Even so, with rough handling the thin of the coax and drilled holes before cable can break – so take it easy. The regulator (and its capacitors) assembly, then slid the 20mm conwere wired point-to-point with the duit length onto the 16mm conduit, minimum practical lead lengths (to made all our solder connections, then avoid shorts) and pushed inside the pulled the 20mm length back out a conduit before the DC socket was bit, pushed all the bits inside, lined up the DC socket with its mounting screwed in. holes and fixed it in place with the The larger electrolytic was chosen screws. not so much by value but by size – as The end cap was then slid hard onto large as we could easily slide into the conduit, while still leaving some the 20mm conduit and the assembly clearance for both the wires and cord. was finished. We didn’t use any PVC jointing compound in case we needed A minimum 25V rating is required; we found a 470µF about the right size to disassemble it (which, by the way, we did to fix a broken cable!). (also ‘cos we had one!). A 1000µF, 25VW would also be a good choice if In use physically small enough. The photo of our video monitor Follow our diagram when wiring the supply and you shouldn’t have any shows just how effective our spy camproblems – but one thing to make sure era is. Inserted into a virtually black cavity, it had no problem finding the of is the connections to your plugpack. Usually, the centre pin is positive but cable of interest – a cable which we had been unsuccessfully trying to there are many exceptions! retrieve for days. If there is any danger of plugging in As we said before, using the camera the wrong plugpack, a series protection diode wouldn’t go astray. In fact, with the image on an angle or upside having said that, there is always dan- down can be a bit tricky – until you get ger of plugging in the wrong plugpack used to it, turn the monitor to match the vertical! especially in many month’s time – so we’ve now fitted (and shown) a 1A When not in use diode in series with the supply. Always store the assembled unit The 2.1mm DC socket may cause you some problems. Most available either on a shelf or supported in at least 6 places. The 16mm conduit these days are too big to fit inside especially is very flexible and will the conduit – we used a PS-0518 DC sag significantly, taking on that shape socket from Jaycar which, with a bit semi-permanently after a while. SC of convincing, fits in!