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Thread: Auto brightness with PIC (PWM) and LDR for Lilliput 701 LED Backlit

  1. #31
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    Quote Originally Posted by rEegLer View Post
    ... everything would be different with a fluorescent model.
    It may not be that different for fluorescent types... you can often still PWM them depending on their PSU. (My first ever 555-PWM was for a 12V fluorescent tube in a mate's car. It merely PWM'd its 12V input - but it was pre-SMPS and was merely a transistor vibrator thru a small transformer. It still worked several years later when he sold the car.)



    Also, earlier I did post a reply to:
    Quote Originally Posted by rEegLer View Post
    Would anybody be interested in a production board?
    ... but it got lost due to full disks....

    I thought the offer was good compared to things like the DigiMotive Dome Light Dimmer (Web Price: $35.00 USD) which fades up and down etc.
    Adding that functionality is merely programming providing the circuit (PCB) has taps/inputs for triggers/switches - and the PIC has program space and copious inputs... (Maybe rEegLer & I should discuss/brainstorm...?)



    I also recently found this electronics-circuits.net Direct Current Dimmer... Its design amused me - doesn't it do the same as the one posted here? (Oh dear, that's the post where I keep replying to myself....
    ...how strange! )
    Anyhow, isn't it funny how some get so lost in the detailed design or fixated on their original approach that they miss the (IMO obvious) simplifications?
    But that is a time-experience thing... (and maybe after a rest or out-of-body experience). Watch how the aforelisted programs improve with time to smaller or more efficient coding as we get more familiar with the chip/PIC and its instructions. (That assumes (1) that the coding can be improved or (2) that there is a need to improve/reduce it.)


    Now, if you guys inspire ME so much as to pull me off my Arduino etc and back into PICs, I'll be very pssed off - and probably extremely thankful.


    And yes - keep up the brainstorming and imagination. LDRs and pots - same thing aren't they? (Ah ha! Establish a preferred PCB layout or resistance range to accommodate both? Should I find & post my "using a LED as an LDR" info & circuit (yellow or red LEDs - not green??? )

  2. #32
    Variable Bitrate rEegLer's Avatar
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    Quote Originally Posted by OldSpark View Post
    It may not be that different for fluorescent types... you can often still PWM them depending on their PSU. (My first ever 555-PWM was for a 12V fluorescent tube in a mate's car. It merely PWM'd its 12V input - but it was pre-SMPS and was merely a transistor vibrator thru a small transformer. It still worked several years later when he sold the car.)
    You're right. They are basically the same. I remember reading that some of the fluorescent inverters actually just use a 5v (0-5v) analog signal to control the brightness which would negate having the darlington transistor unless it required more than 20mA.


    Quote Originally Posted by OldSpark View Post
    Also, earlier I did post a reply to: ... but it got lost due to full disks....

    I thought the offer was good compared to things like the DigiMotive Dome Light Dimmer (Web Price: $35.00 USD) which fades up and down etc.
    Adding that functionality is merely programming providing the circuit (PCB) has taps/inputs for triggers/switches - and the PIC has program space and copious inputs... (Maybe rEegLer & I should discuss/brainstorm...?)
    The PICAXE-14M is somewhat limited in program space (currently 256 bytes) but the PICAXE-14M2 which is set to come out sometime this year has 2048 bytes of available space. The program I'm currently using is taking up the entire 256 bytes but it can definitely be tightened as DavidK showed us with his code above We should brainstorm more. I did quickly whip something up in ExpressPCB and I did allow for future development (placed pads down the I/O's not in use). I might just make my own PCB and see how it works.


    Now, if you guys inspire ME so much as to pull me off my Arduino etc and back into PICs, I'll be very pssed off - and probably extremely thankful.
    You're welcome...

    LDRs and pots - same thing aren't they? (Ah ha! Establish a preferred PCB layout or resistance range to accommodate both?
    They have the same function but act differently. The LDR is a little too sensitive for instantaneous fading (ie If you placed the LDR somewhere by the front windshield, everytime you use your wipers, the screen would dim) but a pot is slightly more stable when it's not being moved (maybe a cap could be used to smooth it out? ).
    Love

  3. #33
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    256B? OMG!!! (Time for tricky assembler code loops.)
    But 2kB - MUCH better. (And I know the other bigger ones... but price...)

    And the code iterations and improvements... What did I write/suggest - addictive; inherent; natural?
    Am I rapt? Blood oath! Impressed? Ditto! (These progressions should be normal stuff in an ideal world, but in the real world... It's so nice conversing with ideal people for a change!)


    And pots & LDRs - I meant "in principle" - ie, both analog; change "top & bottom" resistors to effect range; and allow for a cap anyhow (for noise filtering - typically a small 0.1 or 0.01uF etc).
    I took "instantaneous" LDR change as implicit - but hence with say a 1 second cap filter as opposed to RF etc noise filter for a pot.
    But you knew what I meant...
    Yes - I typically discuss high-level and in-principle for things like this at this stage - the (trivial - yet not!) detail comes at detailed design stage - ie, the PCB (from the "universally adaptable and versatile and expandable circuit for all things conceived and yet to be conceived for all time but still simple and cheap" circuit...).

    Maybe I should hit the sack before my head also starts to hurt. (it's nearly 04:50 here...)

  4. #34
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    Too late my head already hurts

  5. #35
    Variable Bitrate rEegLer's Avatar
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    Yea my head hurts too... Oh well
    Love

  6. #36
    Variable Bitrate rEegLer's Avatar
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    Does anybody have any info on the 669GL-70NP model? Like what the voltage/current rating is for the backlight? The more I know, the better we can change the code/PCB to better suite everyones need.
    Love

  7. #37
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    I don't sorry but I have another monitor that I am looking at that I might like to make it work with..
    http://www.mp3car.com/lcd-display/14...01-36-s-h.html
    No idea how easy it would be etc.. But this is looking like a better option for me than a lilliput.. Just waiting on more information at this stage and to do some planning..

  8. #38
    Variable Bitrate rEegLer's Avatar
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    That's a good price. It is really just a kit which is ideal for most CarPC people. Looking at the pictures, I can't tell exactly how the backlight works but I did notice in the description that the backlight only consumes 15-25mA which is insanely low (but I don't know the operating voltage so who knows).

    ---------- Post added at 11:01 AM ---------- Previous post was at 09:47 AM ----------

    Also I noticed that it doesn't say whether it requires a regulated 12V source and since they don't mention it, I assume it does. With the production board, there is a 12v tap that allows you to power the monitor or other devices.

    Are there any other features people would like to see? If the PICAXE-14M2 comes out soon then there's enough room to do a lot more and more pin configurations. You could control fans based on temperatures, control multiple LED backlights, and so on.
    Love

  9. #39
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    How hard would it be to take two inputs for the brightness? Haven't finished thinking this through at all but you could have a light sensor to do most of the brightness control then if it is too different you could tweak it with a pot.. Might lead to conflicts though for example the screen is too bright still so you turn down the dash and then have no dash lights.. Hmm yeah probably not useful..
    I had a few ideas but can't think of them at the minute...

    Also yes good price although someone mentioned it is only 280 nit which seems a bit low when the high brightness monitors are generally double that.. Waiting to see if it is bright enough anyway..
    Maybe I could transplant a high brightness back light from a lilliput..

  10. #40
    Variable Bitrate rEegLer's Avatar
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    Configured correctly it could measure a couple more inputs. You could simply replace the 10kOhm resistor in the booths divider with a 20k pot and that would allow you to simply change the LDR value.

    Transreflective screens IMO don't need to be as bright since they're using the sunlight to enhance it but I haven't had any experience with them.
    Love

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