Is it possible to modify a digital alarm clock as a timer power switch?

Discussion in 'The Projects Forum' started by Garrettmarvel, Dec 28, 2014.

  1. Garrettmarvel

    Thread Starter New Member

    Dec 28, 2014
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    i have an automatic pet feeder prototype that i’m trying to develop where I’d like to use an off the shelf digital alarm clock to act as the timer to start the power flow to a DC motor?

    in my ME mind, the chip that is given the instruction to make alarm speaker beep should be able to somehow be modified to initiate power to the motor.

    is this possible? or does a custom board or chip have to be designed?

    my hope was to hand modify a few digital alarm clocks and integrate them into the prototype to save money on EE custom design costs for a small run of prototype builds, since a simple alarm clock function and LCD screen, buttons, etc. is what i need to just turn on the motor when the scheduled alarm time occurs.

    any thoughts?

    thanks!

    garrett
     
  2. tcmtech

    Well-Known Member

    Nov 4, 2013
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    You could just buy an off the shelf programable timer and use that.

    The local home building supply center here sells the cheap ones for around $7 and they can be programmed for up to 20 on/off events per day.
     
  3. Garrettmarvel

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    Dec 28, 2014
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  4. ebeowulf17

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    Aug 12, 2014
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    Two rough ideas come to mind as possibilities. In both cases, I'm imagining a simple 555 timer circuit activating a power transistor for the motor control:

    1) Replace the alarm clock speaker with a suitable, low coil voltage, ac relay. When the relay closes, it would start the timer circuit. You'd have to measure the voltage being fed to the speaker and measure the current through the speaker to figure out if there's a relay that the speaker's amplifier circuit can activate. Also the frequency content of the speaker signal could be bad for driving a relay. This could be a truly awful idea - I don't know, but I do like the elegant simplicity of just replacing one magnetic coil in the alarm clock circuit with another. Hopefully people way better at this than me will weigh in on why not to do this.

    2) The other idea would be to run the speaker leads through a rectifier to convert ac to dc, use voltage dividers and/or clamping diodes to limit the voltage to an appropriate range, and then use the resulting low voltage dc signal to trigger the 555, either directly or by activating a transistor switching the proper trigger voltage. This too may be a terrible idea, but this thread is quiet so far, so I thought I'd give it a shot!

    Seriously, I occasionally have a good idea, but mostly I'm really new at this, so don't act on any of my advice unless some of the experts chime in!
     
    Last edited: Dec 30, 2014
  5. ScottWang

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    Aug 23, 2012
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    I also have the same idea, because the timer is cheap and easy to get, there are two ways to do, the one is more complicated, you need to modify inside of the timer, the other one is to buy or design a sound control relay switch on/off circuit, or control relay on and using the key to reset the relay.
     
  6. blocco a spirale

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    Jun 18, 2008
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  7. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    You could certainly use a digital alarm clock, but a custom board would still be required for the interface circuit between the clock and the motor :(.
     
  8. Garrettmarvel

    Thread Starter New Member

    Dec 28, 2014
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    thanks everyone for the help here!!! as an ME, i'm admittedly EE handicapped, but i do understand the suggested directions in basic terms...

    that said, can anyone tell me an estimate of time, cost, and degree of difficulty to accomplish the circuit and modifications needed?

    here are two digital clocks i'm favoring, and a photo attached of the Dynex clock speaker connection points next to the driver chip...

    http://www.amazon.com/Dynex-DX-CLTR01-Clock-Radio/dp/B006OO7DRY/
    http://www.amazon.com/gp/product/B00NG6GIAG/
     
  9. Brownout

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    Jan 10, 2012
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    Time: Couple of hours
    Cost: Couple of bucks
    Difficulty: Couple of degrees

    I wouldn't try to use the speaker outputs. If I could find a digital signal that turns on a buzzer of some external actuator, I'd use that. You might be better off finding a digital clock module kit rather than a finished product. You'd get better documentation.

    Or just use something like this, remove the buzzer and attach wires in it's place.

    https://www.sparkfun.com/products/10930
     
    Last edited: Dec 30, 2014
  10. elec_mech

    Senior Member

    Nov 12, 2008
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    Welcome to AAC.

    The problem with trying to hack an alarm clock is the output signal to the buzzer. It is going either be an AC signal or a pulsing DC signal which will require an additional circuit or two to do what you want. You have to receive the first pulse of the alarm signal, ignore the rest, turn off the alarm, and have a timer to shut off the motor afterwards.

    I like Brownout's suggestion, but the same problem is still present, although it use a piezo buzzer, so you could put a transistor between the output and your motor and it may be enough to drive the motor (via PWM).

    As an ME myself, allow me to suggest making your own circuit. In this way, you can have it do whatever you want from the very beginning. You could use a PICAXE which is a very simple microcontroller that is programmed in BASIC. Ultimately, you wouldn't use it for production, but for prototyping it very inexpensive to get started with. I'd use a PICAXE 08M2 with a DS1307 clock IC and an Adafruit display like this or this. You could put this all onto a breadboard or a cheap strip board. I can put something together and even get you started on the code if you'd like.

    Another possibility is using the microcontroller itself as the interface between an alarm clock and your motor. I haven't tried this before myself, but it's doable in theory.

    We'll need to know more about the motor such as the voltage and current required to drive it and how long you need it to run for. If it requires something special like PWM (speed control), we'll need to know that too.

    Good luck in whatever path you choose.
     
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  11. ScottWang

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    Aug 23, 2012
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    The below was the circuit that I designed for a applause control about 6 years ago, the cd4013 can be modify to works for 3 ways, the one is to turn relay on/off repeatly when it was triggered, the second is to control relay only turn on once and using the key to reset the filp flop and turn off the relay, the third is when the cd4013 flip flop was triggered then it can be a timer, it means that the relay only turn on for a period of time.

    The timer I bought was alarming about 60 seconds, so it will be a long alarm, and it can be triggering many times, so you have to decide which way you want to use.

    SoundCtrl-1-20061028n-eng_ScottWang.gif
     
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  12. Brownout

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    Jan 10, 2012
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    Damn, you're right. In that case, I'd add a transistor and filter to convert and rectify the voltage. Or else, cut and jump the trace to a digital output and make a simple edit to the source code.
     
    Last edited: Dec 30, 2014
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  13. Garrettmarvel

    Thread Starter New Member

    Dec 28, 2014
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    so it sounds like it would be a small job ultimately, as i had hoped. the circuit ScottWang posted is cool but may as well be Mayan Heiroglyphs to me for how it works... i see the grounds, resistors, power sources, and maybe some amps - but i have no clue what its doing or how it works and what it does. LOL.

    the motor my prototype currently uses is this though w/o the gearing: http://www.jameco.com/1/1/4863-rs003a-75-1-metal-gearmotor-6vdc-133rpm.html

    two reasons i prefer the digital alarm clock hack is the LCD appearance for an end user, the cost is cheap at approx. $10, and they are dual alarm clicks with 2 scheduled alarm settings which is key for the product. see short promo video for product reference and purpose.


     
  14. elec_mech

    Senior Member

    Nov 12, 2008
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    If you program your own microcontroller you can have as many scheduled settings as you wish. If you prefer an LCD, would something like this work? There are several color options from other suppliers as well. You can get grey text on a blue background or blue text on a black background to name a couple. You can have it provide clear instructions to the user when programming and even add a countdown to the next feeding time as well as the current time. In the long run, you'll probably work with an LCD manufacturer to make a custom display, but this would give you a proof of concept.
     
  15. Garrettmarvel

    Thread Starter New Member

    Dec 28, 2014
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    it might work, but at size and cost of $25 plus other required components it becomes more cost prohibitive than anything else when compared to $10 for the off the shelf clock, i think....
     
  16. ScottWang

    Moderator

    Aug 23, 2012
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    Mic → Amplifier → RC High frequency filter and isolation → Schmitt Waveform converter → Diode Cap rectifier → filp flop → Bjt → Relay.

    If you like then you can using logical level Vgs mosfet to replace the bjt and no needs to use relay.
     
  17. elec_mech

    Senior Member

    Nov 12, 2008
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    We can find less expensive LCD's, I just linked to one I knew off the top of my head - assuming so, is the size okay for your prototype? How many prototypes are you shooting for?

    Alternately, we could use a microcontroller to interface with an alarm clock to handle all the items I mentioned earlier. About $10 for a programmer and $4 for the microcontroller itself and maybe a $1-3 for additional parts (resistors, PCB, transistor, etc.).

    Scott's solution is certainly an option too. You'll have to ask him about assembly if you want to give that a shot.
     
  18. Brownout

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    Jan 10, 2012
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    Look at page 60 here: http://www.atmel.com/images/atmel-2486-8-bit-avr-microcontroller-atmega8_l_datasheet.pdf The pins connected to the buzzer can be reconfigured to simple digital outputs, so no hacking of the board would be necessary. This is just one kit I looked at. You might find a cheaper one doing more research.

    If you use a kit like this one, we could help making the program hack to reconfigure the pin.
     
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