Littlefoot Elegance Photo User

Astroforum rund um die Astro-Elektronik


Sunday, 26 August 2007

Webcam Modifications 2

I used the prototype for approximately 3 months with some degree of success. In the end I decided that a Peltier cooled camera was a bit over-the-top when used in conjunction with an ETX90. The tracking ability of the ETX drive could really do justice to the long exposure capabilities of the camera. With a 135 mm lens mounted on the camera, piggybacked on the ETX, it was possible to track objects, without trailing, for no more than about 40 seconds. At these exposure times it is debatable whether Peltier cooling is worthwhile. It was also a chore to set up the power supply each time. Also, the weight of the camera was taking its toll on the ETX drive.

Two Tune-Ups later, enough was enough. I decided to take a soldering iron to my trusty Vesta 675, with the intention of building a more practical long exposure webcam.

Vesta 675 SC2, Fan Cooled

I got rid of the egg case and mounted the CCD, still in its metal enclosure, and the circuit boards in a Maplin Project Box. The box is long enough to mount a 12V CPU fan in the base. The fan is mounted to suck hot air out of the box. I drilled holes around the front of the box where the CCD is mounted. In this way the cool air first hits the CCD and is then drawn over the electronics and into the fan. The fan is powered straight off the USB 5V supply. The daughterboard with the 4066 circuit is mounted underneath the main board.

Using an extract fan allows you to control the flow better. Cold air is drawn in by the fan, where you want it to be. In my case the cold air hits the CCD area first. It is then drawn over the circuit boards. In this way I get maximum possible cooling of the CCD, and the hot air rising off the PCBs is drawn away from the CCD, through the fan. This arrangement cools the area around the CCD to within a degree of room temperature. With the fan disconnected the temperature inside the case rises by 8 degrees Celsius.

The CCD enclosure and circuit board are fixed to the box with the threaded body
of the original lens unit. The original lens is removed, through the front of the holder, after breaking off the bezel in front of the IR filter. Keep the IR filter. This can be remounted as shown in the next photo.

The parallel port connector is on the LHS of the box. It is a 5 pin mini-DIN socket. I use a lead from a trashed mouse for the connection to the parallel port. I mounted the tripod socket in the base, insulated with tape, to prevent shorting of the daughterboard circuit tracks. The Box is a Maplin YU53.

The fan is a JAMICON Model JF051SIM. Its rating is 12VDC 0.08A. Diameter is 47mm. I salvaged it from an old 486 PC. You should be able to get a similar model from your local pc dealer. Make sure that the fan turns very easily by hand. Some fans are quite jerky as you turn them. Those ones are unlikely to work off the 5V USB supply (I know, bought one).

Here is an exterior shot of the completed camera.

Note, I've now replaced the original lens mount with the PK bayonet from my 680 prototype. I found that the plastic lens rear protector was not secure enough to hold my 200mm telephoto lens.

With this camera, I have been able to produce my best images to date. It is light weight, provides adequate cooling to allow 40+ second exposures without saturated hot pixels, and it also looks the business, in my opinion.

Even more modifications.

No comments: