Astronomy

Webcam Modification

Steve Chambers invented and made available (see copyright notice) a method of re-wiring a CCD based webcam so that the normal minimum exposure of 25fps could be overridden to give long exposures suitable for astronomy. The cheap astro imaging device was born and the modification named in his honour "SC". My main motive for doing the SC1 mod was that I needed an autoguider for my 14” scope which is driven by Mel Bartel’s Scope Drive system and usually images via a cooled CCD camera. I had played around with various methods of PEC control with some success but not enough to achieve my aim of 2-5 minute 'unguided' CCD exposures. 

The Camera> I didn’t want to risk my precious ToUcam so I posted to the QCUIAG group regarding a cheaper alternative and Arthur Edwards quickly replied that he had discovered and modded the D-Link Netqam Pro. This is a CCD based camera with the ubiquitous 16510 control chip and was available from Scan computers for just over £23 inc. P&P. My order soon went in and I searched around for the other components, again with the help of the many excellent webpages of QCUIAG members.

Before modding the cam I tested it out of the box on my Windows XP Home system. The Scan website gives a download link for XP drivers which I used. XP didn’t like the unsigned drivers but I continued anyway. After a re-boot the camera was still not visible as a USB device in windows explorer but when the DIVPCAM.exe camera software was launched it detected the camera and gave an image on the screen. The cam is cheap and cheerful and so doesn’t give as good an image as my ToUcam in low light. Typically, there appeared to be some 50Hz interference from the PC monitor which can be improved by checking the 50Hz option in the software setup.

Time to bite the bullet. The NetQam guts came out of the case easily once two small screws were removed. The circuit board easily separates into two halves via a 20-pin connector. I decided to try and leave the CCD housing in place to protect the CCD during the work as most of the action would be on the rear side of the PCB. I followed John Taylor's instructions for making a cut across the PCB tracks instead of the pin lifting method.

 The Control Board > I started out by building the simple control circuit with the 4066 IC. I’m not an electronics buff but can follow a simple diagram and translate this to stripboard. The diagram provided by Arthur was the easiest to follow for me, I have added the serial output to the diagram here. I just took things slowly and carefully and inspected each solder joint with an old eyepiece to check for ‘dry’ joints and bridges. I also numbered the pins on the board so as not to get confused! John Taylor pointed out that pin 10  should be pulled to +5V by the switch to enter the long exposure (LX) mode and not as in this diagram. I tried reversing the connections and the cam does not work properly - so for whatever reason use this diagram.

Tools> Once the control board was made I waited until the next evening to do the brain surgery  on the NetQam PCB. Use of Maplin’s 'helping hands' device was a must  as well as a strong magnifier and preferably a low power microscope. I was fortunate enough to acquire a nice 30X binocular microscope some years ago which proved invaluable. You could do the job with a magnifying glass but the microscope gave that extra security to know a solder joint was OK.


Brain Surgery> I made the cut across the three tracks with the tiniest jewellers screwdriver inspecting for any bridges from broken copper track along the way. I then began the soldering. In retrospect I should have used a much smaller point on my soldering iron as the areas to solder are extremely small – make no doubt about it! Even tinier gauge wires would have also helped. The pins on the connector block were relatively easy to solder being raised above the board, the most difficult were the pads. These tended to cover over with the melted green solder mask of the PCB and thus make them impossible to tin with solder. After an hour or so I tried a different technique  by cutting a minute piece of solder and placing this over the pad then applying the iron – this worked very nicely. All this time my enthusiasm was sinking as I thought I had probably damaged the 16510 with heat. 

With all six wires attached, I carefully applied some silicone bathroom sealant to fix the wires in place. I used this, as I didn’t have any hot melt glue. Although the silicone releases a little acetic acid on curing, I didn’t feel this would be troublesome to the board and components and it worked ok. I also used the silicone to lightly fix the finished board in place in the case. The next evening I wanted to move on to connect the control board but as soon as I started work a couple of the wires fell off! Too little silicone! If you are sure of your connections put masses of glue or silicone on to hold the wires in place. With the experience under my belt I quickly soldered them back on and proceeded to attach the wires to the control board. This was the easy part and my enthusiasm started to rise again as the finished article was not far away.

Parallel to Serial>  The parallel port of my PC is occupied with the output from my CCD camera, an old Starlight Xpress SX camera. I thus needed to control the webcam from the serial port and sure enough there were two very similar circuits available to do this. One from Steve Chambers and the other from Peter Katreniak. I built Peter's circuit and put the board in the same plastic box. 

The conversion just did not work. My 'problem' was that I only had 2 wires out to parallel port pins 2 & 21 and both circuits showed more connections...what should I do? John Taylor very kindly exchanged e-mail's with me which proved a great help and nearly got me there. An e-mail to Steve Chambers revealed that serial pin 9 needed grounding in my case, not pin 5. The result worked! In the end this simple circuit proved to be much more of a headache than the SC1 mod.
The next step will be to try out the camera on the guidescope and some real starlight!