Index
Home
Next: Synchronization Circuit Board
3 Cameras
The board cameras that are candidates for this project must meet certain requirements: it should use a single-chip sensor, generate NTSC video, provide three signals needed for synchronization, and operate at power levels that allow battery operation.
Single-chip sensor The very first requirement is that the camera should be based on a single-chip video sensor. Mulit-chip cameras would require access to documentation for the various chips to identify pin functions and timing. Since a lot of this documentation may be no longer available (remember, we're talking about obsolete cameras no longer in production), qualifying a single-chip camera is a more manageable challenge. Just probe the pins for a signal that looks like a positive-going vertical sync pulse, with a period of either 16.6ms (field sync) or 33.2ms (frame sync). If that's available, look for another signal nearby that looks like a square wave with a 33.2ms period (odd/even field). If these two are available, then another pin nearby will be the field sync input. Identify pins near the FSO and FODD outputs that are at or near ground level. Then turn off the camera and check those pins for ground. The one that's not connected to ground (hopefully there's only one in the area) should be the field sync input pin. Section 4 contains timing diagrams for these signals.
The camera must generate video compatible with American television receivers and the VGA converters described earlier. While this book is limited in scope to NTSC video, cameras do exist that provide PAL video output, and VGA converters are available that can use the PAL format for input.
Three signals are needed to synchronize two cameras: FSI (Field Sync Input), FSO (Field Sync Output), and FODD (Field Odd/Even). The input signal, FSI, is absolutely required. You can't get away from it. If the camera does not have this signal input, then it can not receive any synchronization pulse from the other camera.
FSO is a vertical sync pulse that occurs during the vertical refresh period of the video signal. Figures 6 and 7 show FSO timing, and relationship to the video signal.
The third signal, FODD, indicates whether the current field in an interlaced frame is the first (odd) or second (even) field. The reason this signal is needed is to establish a predictable start to each frame. The first field is taken from the left camera. Since the right camera is reset on each incoming sync pulse, all fields generated by the right camera are the first (odd) field in the frame. It is important that the odd/even signal be used, in other words, that the video timing of each field fits the requirements of the television receiver. In order to display the field-sequential stereo video on a television set, two adjacent fields must add up to a frame, otherwise the displayed picture will tear and be distorted.
The odd/even flag is used by the sync circuit board to gate the left camera's odd field, and the right camera's even field, to the output video stream.
If the odd/even signal is not present it can be created using the LM1881 Sync Separator chip. See the VGA Adapter in section 5 for an implementation of the chip.
The camera should be able to be powered by a battery. Single-chip video cameras are able to operate with an input supply of 7-12V, and consume 35mA or less. The camera used in this project consumes about 28mA at 12V. Some cameras require regulated 5VDC rather than the range of 7 to 12V. In those instances, an external regulator will be needed.
Figure 6 Frame Sync Out Signal Timing
Figure 7 Relationship between FSO and Video Out
3.2 The camera used in this project
Smart Vision Products manufactures various types of CMOS sensor chips, including single-chip CMOS color cameras, and also board cameras using these devices. The camera module used in this project uses a board camera, which contains one of their chips, the SVP-OV7500. Today, this board camera can be found on the surplus market. The URLs and addresses of two sources are listed at the end of this chapter.
There are at least two varieties of this board camera on the market using this chip. These are the V-X0095 and the V-XA095. The difference between them is the connector on the back of the board: the V-X0095 has a 6-pin connector, and the V-XA095 has a 4-pin connector. Table 1 shows the pinout of the connectors, and figure 9 shows connector placement. It is also important to know which way is up, since the camera is commonly shown in the literature lying on its side.
It's also important to note that I have never seen the V-X0095; Table 1 and Figure 9 use information taken from the vendors' website, and only assumes the camera is oriented the same way as the V-XA095. The V-X0095 has not been available from the two vendors I am aware of that advertise it, and both vendors will ship you the V-XA095 in its place.
The three signals needed for synchronizing two cameras are FSI Pin (36), FSO (pin 33) and FODD (pin 34). These signals are also referred to as Frame Sync In, Frame Sync Out, and Odd/Even, respectively. See figure 10.
Figure 8 Project Camera Modified with Connector and Base Mounting
| Pin # | V-X0095 | V-XA0095 |
| 1 | Video | Video |
| 2 | Ground | Ground |
| 3 | Power 7-12V | Power 7-12V |
| 4 | Frame Sync Out | Ground |
| 5 | Frame Sync In | - - - - - - - |
| 6 | Pxel Clock Out | - - - - - - - |
Figure 9 Rear View of SVP Cameras
Figure 10 OV7500 Pinouts for Sync Signals
In order to get to the signals needed for synchronization the V-XA095 must be opened up and wires soldered to three pins.
Things you will need:
- low-power soldering iron
- soldering tip with a narrow enough point to solder fine-pitch components
- low temperature solder
- magnifying glass
- holder for the magnifying glass and the board
- three short lengths (around 4") of 30 gauge solid wire, preferably of different colors
Remove the lens housings of both cameras by unscrewing the two screws located in the protruding notches. Once the housing has been removed, be very careful not to touch the transparent lid of the sensor element. Not only will you leave smudges, but also you could damage the device through the lid by electrostatic discharge, if not through the initial handling, then through rubbing the lid to clean off the skin oil.
It is not necessary to solder all three wires to both cameras. One camera will be dedicated to the left side, and the other to the right side. The left camera only needs the frame sync and odd/even wires added and the right camera only needs to the frame sync input wire added, cutting the number of wires to solder by half. On the left camera, the wire colors should be different so you can determine which signal is which. So for the rest of this section there will be a "left" camera and a "right" camera.
3.3.1 Modifying the left camera
The two lengths of wire should be differentiated by either color, or some sort of attached label, so that if you solder both wires to each camera, you can tell in from out. The length of wire needed to go from any pin around the chip, out the exit hole and down to the PCB shouldn't need to be more than about four inches.
Figure 11 shows a drawing of the front of the camera with the lens removed. The three wires shown, one blue, one red and one black, show connections for both cameras. The red and blue wires are soldered to the left camera, and the black wire is soldered to the right camera. Figure 12 shows a photo of the left camera wiring.
Figure 11 View of front of the camera with lens removed
For orientation, an outline of the connector and the oscillator crystal are shown in Figure 11.
Figure 12 Photo of the modified left camera chip
Solder a 30 gauge solid wire on pin 33. On the right camera, solder another 30 gauge wire to pin 34. Route the wires around the chip to the small hole right next to the lens mounting hole. Re-install the lens housing. Be sure the wires are kept as close as possible to the chip to avoid getting them caught under the housing.
Figure 13 Photo of the modified right camera chip
Anchor the wires at the rear of the camera to prevent them breaking through metal fatigue. Create a small harness by tying the power and video pigtails together the two wires added with a piece of string.
3.3.2 Modifying the right camera
The right camera is modified in the same way, with this exception. Don't solder any wire to pins 33 or 34 (unless you really want to do all that soldering) and solder a wire to pin 36 (frame sync in) instead. See figures 11 and 13.
3.4 Preparing the camera mount
Since the V-XA095 camera does not lend itself to easy mounting, a mount must be built for each camera. Figure 15 shows pieces of Lexan added to the bottom of the camera, which can then be attached to the base.
Figure 14 Camera mounting detail
Figure 15 Photo of camera mount
The base and parts A and B in figure 14 are composed of approximately 3/32" thick clear Lexan. Part B is about 11/2" long and 3/16" wide. The two pieces labeled A are about 5/8" long and 3/16" wide. The two A pieces are glued on top of the B, keeping a gap between them of about 1/8" for the bottom camera PCB mounting screw. After giving the glue time to set, two holes are drilled on each end of the mount for 4-40 screws.
The camera lens housing is then glued on top of this assembly, taking care the glue doesn't touch the PCB.
Now the cameras can be mounted onto the base using 4-40 screws, nuts and washers.
There is one last step to finish the mounting. Later, while checking out the video on a TV or VGA screen, you may discover that the vertical height of objects in one view may be different from the other view. This is caused by the two cameras not being exactly parallel. If one view appears to be lower than the other, remove that camera, and lay down two to four layers of cellophane tape along the front edge of the area where the camera is mounted. Then install the camera and check again. Continue until the same point in both views is in the same horizontal plane.
Figure 16 Camera to PCB connections
The cameras that are used will have several wires that need to be attached to the printed circuit board. The V-XA0095, for example, has a connector and harness with four 24-gauge stranded wires - input power, output video, and a ground return for each. Then there are the solid 30-gauge wires that were soldered to the video chip.
The bill of materials specifies a Molex PCB housing, connector body and crimp pins to terminate the camera wires on the printed circuit board. The crimping tool used to attach the pins is a Waldom W-HT-1921, which crimps 30 through 18-gauge wire onto .063" and .093" pins. If necessary, the wires can be soldered directly to the printed circuit board.
The V-X0095 was chosen for the project before other cameras were found which also provide the necessary signals. The OV7500 is not the only chip camera that has the signals needed to generate stereo video.
Unfortunately, it is not always easy to tell which cameras do and which do not, but a small investment in cheap board cameras has shown that many do. In fact, many color and monochrome single-chip cameras have Smart Vision Products sensors.
And also, because these cameras are obsolete and surplus items bought in bulk, there is usually very little documentation to accompany them.
Jameco (http://www.jameco.com) has a color board camera (part number 171011, $59.95) which has the same signals on the same pins (FSI on pin 36, FSO on pin 33 and FODD on pin 34) as the OV7500. It is reasonable to assume that this board camera is also based on a Smart Vision Products sensor.
A cable is included with this camera that matches the six-pin connector at the rear of the camera. The cable breaks out to an RCA connector for video and a power connector for 7 - 12V DC input.
Figure 17 Jameco's Camera, front view
Figure 18 Jameco Camera, Video Chip
Figure 19 Jameco Camera with Cable
I purchased two cameras from Jameco using the 171011 part number. What I received was two slightly different cameras. While they had identical lens housings, the printed circuit boards were subtly different. The cameras were only tested for output video, and for presence of the signals needed for synchronization. Building mounts for the two cameras and testing them as a pair are tasks that are still pending, but I suspect there is some chance, though probably small, that the two cameras may not play well together.
There is a chance Jameco considered the two cameras to be adequately similar to be sold under the same part number. It is also possible they are indeed the same camera, though probably a different version (or revision).
Qkits (http://www.qkits.com) sells the QM3086, which is a monochrome, single-chip board camera. The QM3086 has a sync input and output, but these signals are really frame sync, not field sync. This is not a real problem, since the sync circuit board will take field sync from the left camera and convert it to frame sync to send to the right-side camera.
However, the odd/even signal needed to switch the left and right video outputs is not available. Without this signal, extra circuitry will be needed to generate that signal from the video stream of the left camera.
Figure 20 Qkits camera, Front View
Figure 21 Qkits Camera Video Chip
The QM3086 probably does not use a Smart Vision Products sensor, because of the lack of the odd even signal, and because the sync input and output signal pins are not in the same positions seen on other sensors.
The odd/even signal can be generated using a flip-flop that is clocked by the FSO signal. On the camera module circuit board, the FODD signal is needed to differentiate between odd and even fields coming from the left camera, since it generates a vertical sync signal for every field.
For example, the QM3086 generates only one sync signal for each frame. Simply reset the right camera with that sync pulse (through the reset-conditioned analog switch, of course). It doesn't matter which field comes from each camera, as long as the stereo video output stream contains alternating odd and even fields. If the flip-flop enables the left camera for the even field, then the right camera will be enabled for the odd field. The next time the circuit is powered up, it could enable the left camera for the odd field, and then the right camera will be enabled for the even field.
Electronickits (http://www.electronickits.com/spy/finish/video/cm2.htm) offers the CM2. The datasheet at the site reports this camera is based on the OV5016 single-chip sensor. Examination of the camera shows the three signals are present at the expected pins for an OV7500. This camera is entirely enclosed by a two-piece housing. Three long pins protrude through small holes in the rear section for power, ground and video. The camera is oriented with the three pins aligned vertically on the right side, as seen from the rear. (In figure 23, the camera is resting on its left side.)
Figure 22 Front View of CM2
Figure 23 Rear View of CM2
Also note that this camera requires regulated 5VDC, not the usual 7 to 12 volts that other cameras use.
Figure 24 CM2 Video Chip
As you can see, none of these cameras has a way of bringing the 30 gauge wires toward the rear of the camera for attachment to the printed circuit board. In each case the housing will need to have a small hole drilled into the side for access to the wires. Figure 25 shows a CM2 with a 1/16" hole drilled in the side of the front housing.
Figure 25 CM2 with modified housing
And of course there are many other places where board cameras are sold. The challenge will be to find those sites that provide enough information about the products that they sell, in order to determine whether they can be used.
Index
Home
Next: Synchronization Circuit Board