A simple signal when the dryer is done.

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I have a cheap dryer without a signal to let you know when the clothes are dry. So I'm building one that will monitor when the dryer is drawing power, a.k.a. running and when it stops. Yes there are others, no this will not be IoT enabled. Simple, low power.

  I'm using a split core current sense transformer as the sensor fed thru a circuit that will throw away the negative half of the cycle and use the positive half to charge a capacitor.  I'm using an ATTiny85 to read the voltage on the capacitor so I've added a zener diode to cap the voltage at something that the ATTiny85 can handle.  The Resistor is to insure that the capacitor discharges when the dryer stops.

   The ATTiny85 is kept in 'power down' mode for most of the time, using the watchdog timer to wake about once a second to take measurements by using the ADC converter.  When it detects a charge on the capacitor for more than 10 seconds it considers itself "armed".    When the capacitor is detected as discharged for more than 10 seconds an beeping alert tone will be sounded.  To reduce power usage while sounding the alert I've used PWM and timer interrupts so that I can keep that ATTiny85 in 'idle' more as much as possible.

   I'm planning to run this off of 3 AA batteries and these should last at least a couple of years.



Adobe Portable Document Format - 14.62 kB - 10/12/2017 at 18:25


  • Boards Arrived

    liebman11/04/2017 at 12:55 0 comments

      The boards arrived from @oshpark!  I assembled one and its working!  Next step is an enclosure.

  • Boards ordered!

    liebman10/12/2017 at 20:58 0 comments

        Redesigned to drop the voltage regulator and use 3 to 6 volts. Note that you can't 4 AA's as that will exceed ATTiny specs as they each start closer to 1.8v....  so 3 AA's it is!

       I designed and ordered via OshPark will continue when they arrive.

  • Disappointment - 9v battery bust

    liebman10/11/2017 at 02:37 0 comments

      Initially I wanted to power this with a 9v battery, but the LDO voltage regulators I have draw a quiescent current of 50ua and that would make a 9v batter only last less than 170 days - and most of that power would be waisted by the regulator :-(.   Since the ATTiny85 can run from 2.8->6v I'll remove the regulator and power with three AA's.   *sigh*

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