What's New



Camera Stuff
Tilt-Pan Camera Mount



Email Jim

Tilt/Pan Camera Mount
September 14, 2005
Getting Started
(I can't believe that I have been working on this project for a year.   Besides the normal interruptions, I have had a couple of surgeries on my sinuses that slowed me down a bit.)
This project started back in August of 2004 when I got the urge to buy a video camera.  I think I had seen some security cameras at Costco for about $1000 and thought that "I could do that."  As I began researching cameras, I started thinking about my requirements and what I would like to do with the camera.  Since our son, Michael, is about to start his third year of college, Susie and I have the opportunity to do more traveling.  The idea of being able to keep track of our house and property with a video camera on the web is something that I've thought about for a long time. 

Flash back to me being about age 10 and my folks were looking at new homes.  I was thoroughly amazed by the "then new" intercoms that were cropping up on the model homes of the 1960's era.  Pretty neat stuff for the time.  With the intercom, you could talk to whomever was at the door, or talk to dad in the basement, or the kids in their rooms.  You could even pipe music throughout the house.  Forget the fact that these houses were only about 2000 square feet and you could probably talk loudly and be heard as easily.  I was impressed at the technology none the less.   From that time on, my interest in home automation grew.  Over the years I have done a few intercoms, but nothing too exciting.  Now I had gotten the home automation bug again and it was time to see where this would lead me. 

Looking for a camera was quite a task.  The number of cameras on the market is staggering.  You can spend as low as $25 and top $2000 quite easily without even venturing into the professional end of the market.  As this was my first security camera and I had little idea of where I wanted to take this project, I limited my spending on my first camera to under $300 with the thoughts that if this was something that I wanted to get serious about, I could easily replace the camera.  So far, twelve months into the project, I have not felt a need to jump to the next level of camera - though I may be getting close.

My original camera requirements were just that the camera be able to watch the front of my home - from the street to the front door.  This meant getting a security camera with a tilt/pan/zoom (PTZ) assembly.  PTZ can be performed from a dedicated controller or through the computer.  The computer was the obvious choice for me.  Having the camera and PTZ computer interface would allow me to be able to view and control the camera's view from the Internet.  This would be nice for checking out the house while on trips.  As I continued to research suitable cameras, I found that the ability to "see at night" was well within my price range, but that a weatherproof tilt/pan/zoom was going to be the costly part of the equation.

After finding a camera that allowed viewing color by day and black and white with infrared assist at night, (the 104 LED color camera), I decided that rather than buy a tilt and pan device, I would try my hand at building one.  We'll get back to this a little later.  The camera I purchased is a pretty fair quality unit with a 25 mm fixed lens.  To put this lens in perspective, a 6 mm lens is supposed to be about what your eyes would see, so 25 mm is a close-up or telephoto lens.  (They have a pretty good example of different lens options and the field of view from each here.)  Since this is a fixed lens, the zoom "requirement" was something I wouldn't have to deal with on this camera, but at some point, I would like to either buy or make one.  

Image Sensors
parts of ccd chip (ccd.jpg)The cameras I looked at used either a CCD (Charge-Coupled Device) or CMOS (Complimentary Metal Oxide Semiconductor) image sensors.  There was a time in the not to distant past when the CCD image sensor was the sensor of choice.  Now, both the CCD and the CMOS chips are found in quality cameras, with the CMOS chip being used in cameras such as the $5000 Nikon D2X. In the security camera market, there seems to be more of the CCD chipped cameras in the mid to high quality range, though the CMOS cameras are getting better and are less costly to produce.  This is mainly due to the fact that the CMOS sensors can be manufactured in the same "fabs" (chip fabricating facilities) as for other integrated circuits, like memory.  The CCD sensors use a totally different manufacturing process not shared by ICs. 

The Sony Super HAD (Hole-Accumulation Diode) CCD that comes with the camera I purchased is an improvement on previous on-chip microlens designs found in many security type cameras.  The on-chip microlens has one lens for each of the diodes (also called photosites) that change light into electrons. Sony has been able to reduce the  amount of "wasted" light by changing the lens shape and reducing the distance between the lenses.  More information on the Super HAD CCD may be found here.  Sony now offers what they call the EXview series of HAD CCD chip with enhanced infrared (IR) capabilities. 

IR and the ability to see in darkness has always been fascinating to me.  The ability to see when it is dark is definitely an advantage when thinking about home security.  The image sensors start by converting light into electrons at the photosites on the sensor. With the addition of red, green, and blue filters (additive color system) or cyan, magenta, and yellow filters (subtractive color) for each of the photosites, they are able to produce color images.  However, being able to produce color images has it's cost.  The filters cut down on the available light that hits the photosite so that a color camera has less sensitivity than a black and white camera using the same image sensor.   In addition, because a color camera must dedicate photosites for each of the three colors used to produce a single pixel in the image, the resolution of a color camera is less than that of a black and white camera  using the same image sensor.

Throwing "night vision" into the mix is easy.  Unfiltered photosites (black and white image sensors) are not only sensitive to the range of visible light, but are also sensitive to the near infrared range.  Some chips are better than others for this and the day night camera I purchased is happy to produce images using light in the 940 nanometer range.  In case you've forgotten your electromagnetic wavelengths, they are (approximately): below 400 nm = ultraviolet, 470 nm = blue,  570 nm = yellow,  670 nm = red, above 700 nm = infrared.  The low 700s range of infrared is still somewhat visible as a dull red glow, but 940 is completely invisible to the human eye.  With the 104 LEDs producing infrared energy, the camera has a night time range up to about 60 feet (~20 m) with pretty good brightness and tails off from there.  While testing how well the camera picks up IR light, I purchased a couple of high intensity, infrared LEDs from Radio Shack and wired them into a 2 cell flashlight.  It produces a nice little beam that can be seen by the camera, but not by me or passers-by.  I'm sure the neighbors think I'm nuts when I'm out in the street, in the camera's view, playing with what looks like a non-working flashlight.  Maybe this just confirms my "nuts" status.

Anyway, I am having fun playing with IR.  I have recently purchased 500 IR LEDs and have some ideas for wiring these up beside some low voltage outdoor garden lamps.  If this project works as expected, I will be able to run the visible light if guests are coming over or we will be returning home late.  Once it's time to secure up the house, I'll be able to shut off the visible light and crank up the IR and let the camera watch the property as I sleep.  This sounds like a good plan, but I'm getting ahead of myself and need to get the tilt and pan built first.

There are two accepted ways to approach moving the camera on a tilt/pan assembly.  The first is using servo motors.  Servo motors work by placing an encoder in line with the motor output shaft.  This way, there is a known encoder position for every location the motor can turn to. It is possible to accurately move the motor to the same location time after time.  Servos are common in the radio control modeling world and because of this, there are many moderate cost controllers and servos available.  A standard servo, similar to the Futaba S3003  can be had for about $US10.  The down-side as far as my application was concerned was I *knew* them and wanted to learn about stepper motors.  So, even though I am much more familiar with servo motors, I ended up using stepper motors.  As it turned out, I did learn quite a bit about steppers and found out first-hand the positive and negative aspects of using stepper motor systems..

Stepper motors are permanent magnetic motors that "step" or move one increment each time the controller gives the motor one pulse. They don't require position feedback if run within their limits. When stopped, they inherently hold their position.  This "holding their position without power" mode is usually called the "detent hold" or detent holding ability.  The magnetic field of the permanent magnets hold the motor in position when the power is removed from the coils.  The force that is needed to overcome the magnetic field can be surprisingly strong.  This detent torque will be quite useful in the holding the view angle when using the tilt function of the setup.

Once you power up the controller, each pulse of the controller sends current to the individual coils of the motor.  By turning on and off the individual magnetic fields in a sequential pattern, the motor turns.  There is a good explanation of the different stepping sequences here.  There are many ways of controlling stepper motors through a computer.  You can use a software program to apply power through the parallel port to move bipolar and unipolar steppers.  You may also program the stepping sequences into an electronic logic circuit and use switches, or the serial or USB ports to control the stepper(s).

To start my learning about stepper motors, I dug through the "old parts" boxes in the basement workshop and came up with a couple of 5 1/4" floppy drives.  I salvaged the steppers from these and played around with parallel programming for a couple weeks until I came to the conclusion that this wasn't the interface I was looking for.  While I was researching different ways to control the steppers, I ran across a program that would focus my expectations of this project.  The program is called Motion.  It is an open source project designed to detect motion from cameras.  If you are interested, you can read all about Motion on the Motion Twiki.  I will be revisiting Motion once the hardware is built, but for now, Motion has some support for a serial and USB tilt and pan interface. In fact, they have a schematic for a one axis pan controller. After some thoughts of building my own circuit for a serial interface, I decided on a pre-built controller board from Stepperboard.com.  Stepperboard's BiStepA06 was the board that suited my project the best. 

I ordered one and received the BiStepA06  a few days.  I mounted it in a small project box with a circuit to drop the 12+ volts from my power supply down to 9 for the logic circuit of the stepperboard and a couple LEDs.  The
BiStepA06's circuitry then drops it to 5 volts.  The motor circuits run on the full 12+ volts from the power supply.  I also added a small fan to keep the chips from getting too hot.  I spent the next week playing with C programming and serial ports until I had a basic program to allow my Linux box to talk to the stepperboard.  This time was pretty uneventful until the stepperboard stopped working one day.  An email or two later, I packed up the board and shipped it back to the manufacturer.  It turned out that I may have killed it by static discharge (but I don't think so).  However, Peter replaced the bad parts and shipped the repaired board back quickly and for just the cost of quick shipping that I requested.  I was pleased with the treatment I received and would not hesitate to recommend the product.

So with the board back and the basic program for controlling the steppers written, it was time to order the mechanicals that would make up the tilt and pan device.  I went to Jameco for the stepper motors and purchased a pair of 6000 gram-cm holding torque 12 volt steppers.  These are a bit on the "overkill" side, but having more power than I need is preferable to going the other way.  I also hit Stock Drive Components for some timing pulleys, shafts, belts, thrust washers, collars and flanges.  These were quite expensive for what they were and I had some issues with their ordering software while trying to place my order.  Finally, to end my dealings with them, the order was late in arriving and when it arrived, it was packed extremely well in heavy cardboard with wooden ends, with not a bit of damage on the outside of the box, but the 1/4" diameter steel shaft  that I ordered was bent.  This meant it had to be bent when they packed it.  After spending almost $100 in parts, I expected better treatment.  While Stock Drive is one of the largest companys for gears, pulleys, and other miniature drive components, I think I will try to look elsewhere next time I need to order.

The last order I placed was for some ball bearings to ease the friction a bit in the tilt housing.  I ended up getting these at Tower Hobbies and purchased 10 for the price of 2 at Stock Drive.  These 1/4" by 3/8" flanged bearings happen to be the same as used on a couple of radio control cars I own, so I was familiar with the part and knew that Tower would have a fair price for them.
The last item on the list was what to make the assembly out of.  I gave this a lot of thought and finally decided on acrylic plastic for the tilt housing and wood and plumbing supplies for the base and pan housing.  Yes, I admit that it is a strange combination, but that's me.  I had considered making the whole project from aluminum, but it would have made for a lot more work under the drill press.  Aluminum would be nice if I decided to make more of them, as I would have the housings cast and machined.  However casting a one-off piece is expensive if you don't have the equipment to do it yourself.

Prior to ordering my parts, I spent the better part of 2 weeks working on the cad drawings for the tilt assembly and a couple of days on the pan assembly.  I had been designing the tilt and pan device in my head for about a month now and it was time to get the design on paper and work out the bugs.   I encountered
some items that needed consideration while designing the tilt mechanism.  First, the tilt housing with camera attached had to balance with a camera that mounted from the rear rather than the bottom like a normal camera.  This is why I went with a timing belt rather than direct drive.  The timing belt allowed the motor to be placed in the rear with the camera in front.  The gear ratio is still 1:1.

Secondly, the direction of rotation had to be accounted for so that panning to the right and tilting upward were the same direction.  I first drew the plans backward and only through visualizing the assembly in operation did I realize that I had the motor flipped the wrong way to tilt up with a counter-clockwise rotation (when looking at the front of the motor.)  Yes, you can wire it backwards to make it turn the opposite direction, but it's better to have it right to begin with.

 I made templates for all of the acrylic pieces I needed and proceeded to cut, drill, and tap each of the pieces. I have put together a pictorial of the build process here.  I have tried to put it in some kind of logical order for viewing as the order I built it in was often dictated by which one of the sub-projects I was interested in on that particular day.  It wasn't unusual for me to work on a couple of different parts on the same evening.  When I was doing the drilling and tapping, I would have to take a break and work on something that was more fun, then go back to drilling holes and cutting threads.  The holes had to be drilled as accurately as I could get them, given the accuracy of my drill press. If a hole was off by more than a couple hundredths of an inch, the piece would often have to be scrapped.  I ended up scrapping more than I would have liked to.  This usually happened when I got tired of drilling holes, so I started drilling and tapping some holes in the beginning of the evening and then moving on to another piece of the project after an hour or so.

I had an empty 1U rack case that I decided to use to hold the controller.  As I was wiring up the Stepperboard, I started thinking about sound for the camera.  My camera isn't equipped with a microphone, much less stereo mics, but I was thinking that it wouldn't be too hard to implement.  I was wrong.

Tilt/Pan Security Camera - Introduction
Tilt/Pan Security Camera - Adding Sound
Tilt/Pan Security Camera - Tilt Housing Pictures
Tilt/Pan Security Camera - Pan Housing Pictures

© Fager 7-30-05