dimming illuminator- for bedside clocks etc.

Step 4 Testing

Your assembly should now be ready for power up and testing.
Connect the power source to the board (15-to-18 Volts DC or AC) and expose the photo resistor to a normal bright light, the output LEDS should light up full power (Don't look directly at them, it can hurt your eyes). Next shadow the photo diode with your hand or better still with a piece of black tubing, and the output light should reduce to a very low light. If this test proves OK then you have succeeded, otherwise you need to go back to the previous section and go through the fault seeking order again.
OK your unit works, now its up to you how you use it, for my application, I mounted the board some 1 metre away from the Bedroom clock so that the clock face was evenly illuminated, and it functions very well. If you have other applications you can of course move the Photo diode away from the board via a wired connection and mount it a position better suited for your application.

Comments

[halitus87]

Just a quick question when you first power it on shouldnt the LEDS be off? and only turn on when you shield it? the first paragraph made it sound the other way around Great project though I like it

[brianpxbd]

no sorry, that's the opposite of the desired effect. The idea is that the illumination is just enough to see the clock in the dark and as the light increases, so does the illumination. In other words the light shining on the clock is always a little brighter than the ambient light. I know that sounds crazy, because normally one does the opposite!

[halitus87]

No i agree. I wasnt sure which you were using in the first step you said it was inversely proportional to the ambient light . I think having light proportonal to the ambient light is a better idea. How ever can you incorporate limits into it? so that unless turned off in complete darkness there will still be some illumination , and if the ambient light becomes great enough (ie a sunlit bedroom) the LEDs fade to off as well as they wont be needed. sort of maximum and minimums

[brianpxbd]

OK, Good point about my inverse proportionality Hi Hi, I should have considered my wording a little more. Your idea of limiting both ends of the lighting range is fine. The lower end (Darkness) is in fact limited, however in my application I saw now reason to limit the top end as in very bright light one can ignore the clock lighting, and also the small power consumed by the unit is hardly a problem. Perhaps if someone has a reason for a battery powered unit I would incorporate the high (Bright light) lighting turn off function.Thanks for your comments, Brian

[halitus87]

No i agree. I wasnt sure which you were using in the first step you said it was inversely proportional to the ambient light . I think having light proportonal to the ambient light is a better idea. How ever can you incorporate limits into it? so that unless turned off in complete darkness there will still be some illumination , and if the ambient light becomes great enough (ie a sunlit bedroom) the LEDs fade to off as well as they wont be needed. sort of maximum and minimums