Electromechanical Timer Replacement - 320Volt

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Timer ControllersElectromechanical TimerReplacementAuthor:Bret WaltersInter.tec.Ontario, Canadaemail: bretw@ibm.netSUGGESTED APPLICATIONSEgg TimerThis device could be used in many ways, to solve the“egg timer” example; it could be battery operated andhave one or two buttons. The version shown has onebutton, its functions are stop/clear and start/reset. Tooperate, the button is pressed once for each timer increment.The timer automatically starts counting when thebutton is no longer pressed. Pressing (and perhapsholding) the button again, will stop and reset the timer.Two buttons could easily be used but are unnecessary.For this operation, I suggest an external crystal or RCoscillator to give a slow clock that is then divided. Thisreduces code complexity by not needing as manycounting bits and reduces power consumption. The circuitcould be powered from a lithium 3V cell.Garden Watering ControllerThe device would be powered by the AC outlet in thisexample and drive a opto-isolated triac to produce output,a relay or other device could also be used but atriac is recommended. To drive a DC load a nice powerMOSFET will do fine. Observe the schematic to seehow the PICmicro is powered from the AC line.Since the PICmicro needs little current, the current istaken from a diode which is connected to a simple voltagedivider with a low power 5.1V zener diode and aresistor (5W recommended to prevent overheating dueto power dissipation). The output ripple is removed witha small capacitor, sat 1 µF to produce stable power.Conveniently enough, this now gives a source of 60 Hzaccurate clocking signal that can be counted and usedfor accurate timing. Trimming the clock is no longernecessary! The timer simply debounces and countsthese pulses and compares it to the desired value. Thedesired value is set using the same one-button or twobutton interface as the Egg-timer. The device couldlikely be built small enough to fit in an adapter socket orpower bar.Freezer Life Extender/Motor Life Extender/Power-on Delay CircuitAfter a power failure, the compressor of a freezerbecomes hard to drive due to the settling of the refrigerant.This causes a high load on the AC compressormotor and slowly reduces its life span. Furthermore, theload on the AC line is quite high and if other motors areon the same circuit, breakers can trip.This could be easily averted by building a GardenWatering Controller into the freezer startup and havingno user buttons. The delay would be set to approximately.5 minutes. This delay gives the freezer time toslowly move the refrigerant, greatly reducing load. Plus,the freezer no longer places a load on the AC line at thesame time as all other devices that come back on lineat the end of a power failure.Microchip Technology Incorporated, has been granted a non-exclusive, worldwide license to reproduce, publish and distribute all submitted materials, ineither original or edited form. The author has affirmed that this work is an original, unpublished work and that he/she owns all rights to such work. Allproperty rights, such as patents, copyrights and trademarks remain with author.© 1997 Microchip Technology Inc. DS40160A/1_006-page 1
Electromechanical Timer ReplacementFIGURE 1:SCHEMATIC TIMER CONTROLLER (EGG, LAWN, FREEZER, ETC.)Optional AC Use117VAC In22k5W47kOptional Buttons5.1VVDDVSSOptional AC useGP5GP0GP3GP1NCGP4GP28-Pin PICmicroOptional LEDor Piezo10V1 µF.33k117VAC OutDS40160A/1_006-page 2© 1997 Microchip Technology Inc.
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