Automatic Lighting Box With a Timer on Battery




Introduction: Automatic Lighting Box With a Timer on Battery

I propose a simple lighting scheme of the kitchen drawer to turn off the timer. The backlight is switched on for 15 seconds. (that's enough for me)

Step 1: You See a Box With Light and Without


I propose a simple lighting scheme of the kitchen drawer to turn off the timer. The backlight is switched on for 15 seconds. (that's enough for me)

Step 2: We Need:

  • Magnetic contact 3 pins
  • Magnet D15H4
  • Transistor IRF840 (It can be any n-MOS transistor)
  • Resistor 500 Ohm
  • Resistor 300 Ohm (you can not put)
  • Resistor 20 Ohm (to reduce current LED strip - you can not put)
  • The capacitor 16c 22mkf
  • 25cm LED strip
  • 8pcs AA batteries (rechargeable batteries can not be used - high self-discharge)
  • 1 m double wire.

Step 3: The Scheme Is Very Simple

Step 4: How Does the Magnetic Contact

As I approached a magnet contact switches

Step 5: Solder the Resistor to the Transistor

Step 6: Solder the Remaining Parts of the Scheme

Step 7: Solder the Wires to the LED Strip and Connect to the Timer

Step 8: Assemble Battery Pack

Step 9: Test Duration and Current

Step 10: Set in Place and Glue LED Strip

Step 11: And Put a Magnet in Front of the Magnetic Contacts

Step 12: You Can See the Result.

With and without illumination.

More details you can see on the video.

Thank you for attention.



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    44 Discussions

    I think, reed with 2 normally open contacts will be simpler. There is no need to disconnect 500k resistor when 300 ohm is connected. So it's enough to connect capacitor and R1 constantly and only to connect R2 via just simple normally open reed.

    Ilya, most of reed contacts are able to switch more than 0.5A. You don't need all that stuff, the reed and the magnet is enough !

    13 replies

    The reed switch isn't being used to control the leds current, it's being used as a sensor. When the draw is closed the magnet makes the reed switch connect the capacitor to the resistor, which charges the capacitor up. VT1 is switched off so the leds do not light. When the drawer is opened, the magnet goes off the reed switch which then changes over and the capacitor is then connected to VT1. This causes VT1 to switch on until R1 discharges the capacitor and VT1 switches off again, so the leds then go out. The values of C1 and R1 control the time, the bigger C1 or the bigger R1 the longer the time and vice versa.

    The design is good and simple, but I think it's a little bit of overkill on the leds. I would just use a couple of high efficiency leds and a current limiting resistor in parallel. This would be bright enough and would need a smaller voltage and therefore less batteries. You could then get away with 3 batteries and less leds. You could possibly even get away with one led using a diffuser.

    wobbler... If Ilyanov's chosen C1 & R1 combo for this circuit yields a 15sec. 'on'-cycle... how would one calculate the necessary values of C1 & R1 (in a similar circuit / application) to yield an "on" time of, say, 1-min., for example? Or, 2-minutes... etc.? Is it as simple as raising the "values" by a factor of 4, or 8... to achieve those time-lengths? I'm a complete novice... but, very interested in these sorts of timing circuits.

    Oh sure. You think correctly.

    Increase Capacity Capacitors proportionally - time is proportional to the increase.

    Reduce the resistor is also proportionally increase the time

    The time is propionate to the size of the capacitor and the resistor. If you double the resistor it will double the time. If you double the capacitor it will double the time. You can also change both and it will be the multiple so e.g. if you double the capacitor and triple the resistor it will take 2x3=6 times as long. Similarly if you wanted a shorter time you would use a smaller capacitor or resistor and they would be proportional as well, so half the resistor, half the time.

    What about introducing a 'pot', so one could vary/regulate the 'on-time', at will? I'm not thinking of this particular application, but rather, a "blinking' circuit. How would you determine the 'limits' (min. & max. range of pot); since, I'm assuming that not all LEDs are equal regarding how much applied power they can accept... before they 'fail' or become non-functional. I wish someone would contribute a schematic, with full explanation of how to make it 'blink' randomly, as well as, at consistent intervals. Also, how about having it run on a 9v battery? I'd buy them 'lunch'.

    A long, long time ago I made some Christmas tree led lights which blinked randomly. The way I did it was with TTL circuitry using a gated oscillator. The basic way it worked was I had an oscillator which was continuously running really fast (about 1Mhz) and I had a timer circuit which lasted a longer time. The two weren't synchronised, so the timer triggered a D type flip flop which recorded the state of the oscillator at that time. As a result, whenever the timer triggered the D type flip flop it ended up as either a 0 or a 1 so the leds were then either on or off. So, it was random in terms of on or off and the state even though the state changed at fixed intervals defined by the timer.

    Hope this makes sense, contact me directly if you want a rough schematic. It's also probably possible by using a dual 555 timer chip or going hi-tec and using an Arduino.

    Reducing the resistor will decrease the time as it will cause the capacitor to discharge quicker.

    Oh yes of course.

    I made a mistake. Of course you're right

    again Wobbler,

    Thank you. In a few words everybody understands,

    Go on with your good job.

    I know. I'm only telling that the switch could easily drive the LEDs and nothing else is needed.

    Yes you are right.

    I chose a strip that's why.

    It is flat and thin, has an adhesive layer. (LEDs Diffusers will stick out and I can break off them)

    The light from the strip is much more diffused. I like it more.

    For individual LEDs need damping resistor (which is extra cables and connections that can break)

    And on the strip everything is already there. It is only necessary to connect the two wires.

    For low-voltage transistor logics needed (this will not work)

    I agree with you


    This unit is where inconvenient to connect the power.

    If you do not put off the timer if someone forgets to close the battery drawer quickly discharged from the always-on strips.

    I have a similar setup in my bedroom closet except i use only a micro switch.

    The RC time constant is the time constant (in seconds) of an RCcircuit, is equal to the product of the circuit resistance (in ohms) and the circuit capacitance (in farads),

    So .000022 Farads times 500000 Ohms = 11 seconds roughly. The special transistor drains little.

    If the magnet is not placed correctly the light may come on when closing it too cutting battery longevity in half.

    forgive my noob comment since im not that great at circuits, but what would happen if R1 wasn't there? wouldn't the capacitor discharge either way?

    2 replies

    Sorry, I confused myself
    I am not answered (there were a few questions from different people, and I'm confused)
    R1 - MANDATORY resistor
    Sets the backlight time

    R2 - not necessarily from the reed switch contact arcing protection

    R3 - resistor is not necessarily - to save battery power (the strip is very bright)

    R1 is needed to eliminate spawned reed contacts.
    You can not put.
    I put it on just in case.
    It seems to me as more correct.