LIGHT sensor

[garym999]

The gregorian clock function will be handy but when you are talking lighting control, it does not map to local weather (light) conditions. So a Lux level sensor would still be handy.

Nigel, The implied 75K on page 4 is the approximate resistance at 10 Lux... (ref datasheet). The resistance range just shows how inaccurate these sensors are.

The effect of the sensor wiring (100R) is going to be minimal.

In practice I would suspect external interference or induced voltages in the cable. Is the sensor cable running along side mains cables etc. If the cable is screened this should be less of a problem.

To mitigate this I would remote mount the whole PCB assy in a IP rated clear case and ensure that it is sealed around the cable entry correctly.

Alternatilvely use a mains based dusk/dawn relay. It might need to be modified to produce a set of volt free contacts but I have found them easy to implement and have suitable hysterisis built in (30secs +) so you do not need any special coding to ensure reliable operation. Oh and it is in a weather proof housing with proper conformal coatings to protect the PCB and sensor.

[garym999]

I have the Velleman MK125 kit here on the bench.

It has built in hysterisis but it is implemented rather crudely. It takes about 5 seconds for a switch over but once this has been reached the hysterisis time drops as there are no lockout timming circuits involved. So the implication is that you will still have to program in the reliabilty aspect.

However I do not have any real life experience of it.

[Guest]

I built my own, specifically because I needed two outputs, one for switching indoor lighting and one for switching outdoor lighting. The unit uses only one photocell, but has two separately adjustable outputs. Maybe something worth thinking about if a new light sensor is designed.

[garym999]

Actually a common problem. So a properly designed LSM that outputs an stable analogue value in to Comfort. Then you can use this to trigger different events based on differning light levels.

[slychiu]

There are a number of wireless light and other sensors using Enocean technology which shall be a good option to use with Comfort when the UCM/Enocean is ready

[blowoutbedding]

The ambient light sensor on the newer Unibody MacBook Pro (all models: 13″, 15″, 17″) is available on macbooks. it located directly next to the iSight camera at the top of the display.