How it works#This is a conceptualisation of the entropy condenser. The graphic is a .pencil format export from our 3D pre-visualisation software. Work is currently on-going, and Paul's busy gluing stuff together.
The operation of this condenser is founded upon noise within a CMOS web cam sensor. This is the same sort of noise we all see when taking dimly lit party photos with our mobile phones. The web cam is at the centre of an integrating sphere. The sphere inside diameter is 260mm. This is the de rigour scientific approach to guaranteeing very uniform lighting for optical instrument testing. The web cam (actually it’s focal plane) is at the centre of the sphere, looking at the inside surface. Directly behind the camera and facing in the opposite direction is a white LED. The LED lights up the inside of the sphere, and as the light reflects in all directions and many times, a uniform illumination develops. The sphere coating is not a perfect Lambertian surface but works remarkably well for domestic emulsion paint. Needless to say, the front automatic infra red illuminator has been disabled as well as the network status and power LEDs on the rear of the camera. As the uniform light enters the web cam, it forms a grey image. The intensity of this image is determined by the level of illumination, and the degree of automatic gain as the camera tries to bring the image up to a reasonable viewing level. The LED orientation has been chosen carefully to facilitate a minimum of two bounces for any light rays before entering the camera lens. This is important for uniformity within an integrating sphere. The current to the LED is controlled by an external series resistor and its value is subject to experimentation. The aim is to reduce the LED level to below the point that can be compensated out by the automatic image gain of the camera’s signal processor. This minimum illumination level will maximise image noise and therefore entropy. A major obstacle is that the web cam automatically cuts out and blanks the image if the image level is too low. The trick is to set the image intensity to just above the cut off point for maximum noise generation. There is also a light dependant resistor (ORP12 type) mounted on the rear of the camera, as well as a digital thermometer. The ORP12 allows the light level inside the integrating sphere to be measured relatively accurately. A specific lux intensity is not required, as long as a resistance can be repetitively measured. The thermometer has been incorporated to monitor the temperature within the integrating sphere. This is important as noise levels vary with temperature, and Paul was concerned that the sphere would catch fire due to the power dissipation from the camera. He has estimated a 7.5o Celsius temperature rise due to the insulating effect of 20mm of polystyrene and a roughly 300mA @ 5V power dissipation. Both temperature and photoresistance can be read externally. There are many forms of noise that contribute to the overall entropy within a dark web cam image, some being:-
- Photon noise
- Noise in dark current
- Reset noise
- Sampling noise
- Thermal noise
- Quantization noise
That’s a whole lota noise that gets output in the form a JPEG image sent over Ethernet.
And it's all based around one of these, which sits at the heart of the integrating sphere (the big round thing with the bolts). The retail boxed version is shown in the attachments.
This is the latest design for the Photonic Instrument. The design was completed using an open source CAD package called QCAD http://www.qcad.org. It's akin to AutoCad, but without the high end facilities. It has enough features for small scale professional use, and is where AutoCad was 10 years ago. In our not so humble opinion, it's the best open source 2D CAD package available.
But wait. We've moved onto DraftSight from Dassault Systemes, http://www.3ds.com. This is even better being a virtual clone of AutoCad. It's not open source, but is effectively free and brilliant.
This is a schematic that be updated as Paul gets on with it ...
We can't take credit for the weird pedestal design. That was blatantly copied from a cast iron table leg photo (in the attachments) we found on the internet. Thanks who ever you are.