Light sensor for backlight module

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Light sensor for backlight module

Postby Tranworld » Wed Jun 29, 2011 3:09 pm

I have the backlight installed in my 9x which is great but it does consume about 60mA to 90mA, quite a lot for nothing when our TX is mostly in the sun, building a manual switch is simple but it requires you to remember and you may not notice that the backlight is on out in the sunlight anyway.
The custom firmware such as ER9x has a software switch for the light and a timer too still there is nothing as appropriate as a sensor that switch the backlight on when dark and off when in the sun
This can be done via few components only, namely a FET, a CDS sensor and a couple of resistors, can someone guide my hand as to how to design such a system?
Tranworld
 
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Re: Light sensor for backlight module

Postby Tranworld » Fri Jul 01, 2011 12:45 am

Anybody? I intend to make it very simple:

1 - I add a single FET transistor to pin PB7 as described in the th9x guide, this will allow the firmware to switch the display ON and OFF
2 - Then I insert a CDS to the GATE circuit in such a way that when it is bright the sensor will effectively turn off the FET (even though the firmware still turn it on via PB7).

That way I can leave the firmware to turn on the backlight all the time and have the sensor turning the light off and on as the conditions allows, but I can turn it off ultimately via the menu in the firmware as necessary.

It is in 2 that I need some help, how to I design a very simple circuit to affect the Gate of the FET using the CDS sensor?
Tranworld
 
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Re: Light sensor for backlight module

Postby Tranworld » Fri Jul 01, 2011 5:18 am

In the end it seems a lot of work for what it is so I just soldered a tiny little switch and fitted it on the front panel and turn on the back light as and when necessary
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Re: Light sensor for backlight module

Postby Tranworld » Sat Jul 02, 2011 1:28 am

And....since having the ability to turn it off, I find that I turn it ON more often than OFF :P
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Re: Light sensor for backlight module

Postby disco stu » Mon Jul 04, 2011 4:21 am

I am following, I just don't have the skill to contribute
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Re: Light sensor for backlight module

Postby Tranworld » Mon Jul 04, 2011 6:46 am

What I am saying is that whilst I have built a switch, it is more ON than OFF, I guess when I am out in the field in blazing sunshine it may be OFF more than ON, thus the complication of a sensor, albeit very nice, may be a little too complicated to do than just a simple switch, in my case I was able to find a tiny one that is almost invisible, you can see it here in the last picture
http://www.rcgroups.com/forums/showthre ... 2&page=496
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