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  1. #11

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    Quote Originally Posted by kittyhawk88 View Post
    DIY F Stop Timer.
    The target price should be around $25 -$35.
    I'll definitely go with SMD components onlyto minimise labour..
    What do you guys think..
    I used to be an avid DIYer. I think your estimate is very far off.... Buying just components will cost you about your target price. Add to that, a simple PCB made by a third party will cost $20 or so in small batches. On top of it, switches, case, tooling, and misc hardware will double all that. In small batches, your cost out the door with no profit will approach $100 if not more.

    SMD parts may be cheaper per unit but usually aren't sold in small quantities. Unless you automate the building process, it won't minimize labor but will increase it.

    I think, using traditional leaded components with universal PCB and a simple parts kit without switches or case may be possible near your price.

    I like your idea but economically, I don't know if it's a good idea. (sorry...)
    Develop, stop, fix.... wait.... where's my film?

  2. #12
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    Quote Originally Posted by kittyhawk88 View Post
    DIY F Stop Timer.

    I am toying with the idea of a simple f stop timer. If there are those who are interested. I propose designing a simple DIY f stop timer which is open source around a simple pic chip.

    Some of my thoughts are :


    Simple to use
    Always counts up from 0 to 64 seconds.
    At start switch enlarger on.
    Beep at each major f stop , e.g. 4 seconds 8s, 16 s 32s 64s.
    Provison to beep also at 1/4 or 1/3 stops between major periods.
    e.g. count up to 8 seconds and beep at each quarter stop.
    ability to set range for beeps. - helps with making test strips.
    at end of counting period trigger a rely to switch the enlarger off.

    I can draw a picture of this simple device. But don't know where to post it.

    The target price should be around $25 -$35.

    Shoud use a simple 5V USB plug pack or 12 Volts plug pack.

    1) Make up kits for those who want to solder them up
    2) Make up finished items - small run of 50 units for those who don't wish to bother wiht the above.
    3) Offer schematics and board layout to the APUG members and anyone on the web for that matter.
    5) Wite up the software to control the timer- offer binary and source code to anyone.
    6) Get a repository going for those who want to offer modified code based on the board layout.

    I'll definitely go with SMD components onlyto minimise labour..

    What do you guys think..

    Do you need a simple F stop timer that beeps and lights a red led at each major F stop?

    I'll definitely need one to help me wiht my test strips...

    Please let me know your thoughts.
    I'd love that, and I do kits, but I don't have the stuff to build SMD style. That combination is usually mutually exclusive. I don't think kits really save money these days, unless it's something that requires the boards to be hand-populated and soldered.

    While your feature list appeals to me, you could probably copy an old timer from the 70's 80's and if you had to do a scaled back project. I like some of them, but the switches tend to get corroded or worn out and the caps are probably dried out. It could be redone with modern switching universal voltage power supply, debounced switches, etc..

    Only feature I'd add is a dimmer on the display.

    Another system with potentially less parts and more off-the-shelf would be a USB controlled relay with a computer program to operate the timing functions. The software should be able to be used with a red gel over the display of a netbook/laptop. If it were network controlled and web app based, it could be managed by a ip[hone,ad] or android or other devices as well.

  3. #13

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    Probably the simplest thing we can do is to use something like 2 digit BCD rotary thumb switches for setting up time, one push button for start, pull-up all leads and feed them into input pins of small PIC chip or something. Then take one output pin, use a transistor to drive a relay. The start switch needs to be debounced in software but thumb switch can be read once the start button is pressed.

    This way, there is no display issue to worry about, small parts count, and basically duplicate the function of an old Gralab 300 timer.
    Develop, stop, fix.... wait.... where's my film?

  4. #14
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    Quote Originally Posted by tkamiya View Post
    Probably the simplest thing we can do is to use something like 2 digit BCD rotary thumb switches for setting up time, one push button for start, pull-up all leads and feed them into input pins of small PIC chip or something. Then take one output pin, use a transistor to drive a relay. The start switch needs to be debounced in software but thumb switch can be read once the start button is pressed.

    This way, there is no display issue to worry about, small parts count, and basically duplicate the function of an old Gralab 300 timer.
    I'd want a focus switch as well to turn on/off the enlarger for focusing/composing.

    If you have lots of outputs you could have it control the blower for the big enlargers too. Start the blower up with the bulb, then shut if off 2 minutes or whatever is appropriate after the bulb goes out.

  5. #15
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    I build a 555 based timer from a Popular Electronics project back in 1974. It cost about $25 in parts back then.


    Timer and enlarging exposure meter:
    Last edited by ic-racer; 11-15-2010 at 03:03 PM. Click to view previous post history.

  6. #16

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    Quote Originally Posted by jp498 View Post
    I'd want a focus switch as well to turn on/off the enlarger for focusing/composing.
    Yeah, but you can do that with a simple switch. There is no need to involve cpu or logic with that.
    Develop, stop, fix.... wait.... where's my film?

  7. #17

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    Quote Originally Posted by ic-racer View Post
    I build a 555 based timer....
    Why would you want to mess with that ANALOG crap...
    Develop, stop, fix.... wait.... where's my film?

  8. #18
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    Quote Originally Posted by ic-racer View Post
    I build a 555 based timer from a Popular Electronics project back in 1974. It cost about $25 in parts back then.


    Timer and enlarging exposure meter:
    That's a beauty! I built a NE555 based timer too, but not for photography or darkroom use.

  9. #19
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    My first darkroom timer was a 555 counting seconds into a digital counter which was compared to the input from a couple of BCD thumbwheel switches. When the count and the switch input was equal the circuit would switch off courtesy of a digital comparator.

    I still have it somewhere. I will see if I can find it.


    Steve.
    "People who say things won't work are a dime a dozen. People who figure out how to make things work are worth a fortune" - Dave Rat.

  10. #20

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    Hello !
    You plan to use the timers in a shared darkroom (with possibly child using them).
    I would strongly advise to buy a reputable make/model backed up with compliance to various electrical code and the one relevant to your country.
    A darkroom is a place where electricity and water share a very tight place. And they don't mix.
    So if you make a timer yo MUST ensure no one could be injured by it even by miss use. And you MUST comply with all electrical and safety code ... Quite a job (just to gather the requirements...) !
    Last but not least, when it comes to safety avoid buying second hand. You never know if the unit had been tempered or not (unless you have them checked by the manufacturer...)
    Hope this helps

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