Ken Hough's Website
Astronomy

Projects: Modification Of Webcam for Long Exposures

Practical Implementation

My first attempt at modifying a webcam was not successful. I had decided to do a full SC2 mod. I don't like to do things by halves. Even on an SPC900NC, this required the lifting of pins on the 16510 chip.

I have build and modified electronic circuitry for more years than I care to remember and so felt confident that what others have done, I would be able to do. Big mistake!

Before attempting this kind of mod, it's important to understand that surface mount components such as the 16510 chip are very small and delicate. A good magnifying glass, sharpened soldering iron bit, patience, and A VERY STEADY HAND are essential for success.

This image gives some idea of the size of components relative to a UK 5 pence coin and also my efforts to connect to already lifted pins on a 16510 chip.

Despite my initial confidence, I damaged the pads below the pins when I tried to lift the pins

Not very pretty!

It seems that my eyesight and hand are no longer up to this kind of job.


I bought a second SPC900NC, and decided to do an SC1.5 mod. I then followed the excellent directions given by Mattheus Meijer. This did not involve the lifting of any pins, or working on any surface mount components, and turned out to be very easy to do.

I deviated from the Meijer directions in that I built the extra components onto a piece of Veroboard which also carried components for 'amp-off' according to the Beeke method.

Most of the mods reported in the Internet have been made using 'wire-wrap' wire. This is quite thin and appropriate for connecting to very small lifted pins, etc.

I was planning to add a Peltier cooling system to my webcam. This will include a small fan inside the new webcam enclosure which might cause thin connecting wires to vibrate and to fracture. For this reason, and also because of the nature of the mods that I did, I used thicker connecting wires, stripped from multi-wire ribbon cable.

The new enclosure for my webcam was obtained from Maplin (Part No: LH21 -- ABS Box MB2). Holes were made in this box as follows:

-- in the base of the box to accommodate the plastic surround/protector of the webcam sensor chip, so that the shoulder on this surround butted firmly up to the base of the box, allowing the webcam to 'look out' from the base.

-- in the base of the box to accept bolts to hold the front mounting plate and spacer plate to the base of the box.

-- in the side of the box to accept a 9 pin 'D' type connector to carry LX and amp-off control lines to a computer.
-- below the 9 pin connector, a 15 pin 'D' type connector to carry power for an internal fan, Peltier cooling device, and    connections to an internal temperature sensor.

-- in one end of the box to accept bolts which retain a thick plate (a short length of 1 1/2" x 3/8" aluminium strip) for mounting the webcam on a normal tripod head or similar. The plate was drilled and tapped to 1/4" BSW to accept standard tripod mounting bolts.

Webcam mounted inside box with additional components mounted below on strip board.

'D' type connectors are shown at the right hand side.

LX and amp-off controls are connected via 9 pin 'D' to 25 pin 'D' parallel port via the ribbon cable.

The original USB cable of the webcam is used to connect the video stream to a computer.

An aluminium mounting block has been fitted to the bottom of the enclosure. A tripod quick release clip is shown fastened to the block.

Note: The multiturn 100K pot used in the original Beeke amp-off mod has been replaced with a single turn 10K pot plus fixed resistors selected to give an amp-off voltage covering the range of approx 10v to 13v or so.

Exploded view of front mounting plate, spacer and webcam enclosure showing webcam carrying original lens and 'looking out' from the base of the enclosure. The lens is in place only for testing.
Note:
1. The front plate carries a mounting ring for camera lens/extension tube.
2. The spacer plate has a filter mounting ring glued into it. The mounting ring was made from the body of an unwanted 1¼" eyepiece filter.

Mounting plate/extension tube, spacer and webcam assembled.

Original webcam lens removed, and IR/UV filter fitted.

Complete assembly with 50mm lens and additional extension tube so as to give correct focusing.
The extension tubes are standard Pentax PK mount 35mm camera extension tubes. The rear plate of a 13mm extension tube was removed and the tube was bolted directly onto the front mounting plate. The addition of a 21mm extention tube then provided the correct total distance for focusing of Pentax PK type cemera lenses.This arrangement allows for connecting the webcam to either a camera lens, as shown above, or to a T2 adaptor and hence to a telescope.

Dimensions/thicknesses of parts are:
    Extension tubes -- 21mm + 11.4mm (ie 13mm - thickness of removed rear plate) = 32.4mm
    Front mounting plate -- 16SWG aluminium
    Spacer -- 6mm PVC
    Base of enclosure -- 2mm

The top surface of the sensor chip is lies approximately 2mm inside the inner surface of the base of the enclosure.

Pentax PK mount extension tubes have been used. For other types of mount, it might be neccessary to use different lengths of extension tube and/or different thickness of spacer.

In order to make space to attach filters, the internal baffles and auto apperture parts were cut out from the extension tubes. This allows at least two filters to be stacked inside the combined extension tubes (eg an IR/UV filter and LPR filter).

Tests done with this camera using wxAstroCapture have shown that long exposure and amp-off controls operate as expected.

The tests suggested that this webcam would benefit greatly from cooling of the sensor chip. Unless the sensor chip is moved, the only option for cooling is to cool the whole assembly via an internal fan and a Peltier device. I intended to do this as an 'add-on', fitting this into the lid of the webcam eclosure.

Return To Webcam Long Exposure Index Page

01/12/12