Staircase Light Timer
There are many off the shelf solutions that will automatically turn a staircase light off after a period of time. However, all the ones I've found involve adding new wiring and switches, which just isn't practical in our house.
This project is the result of many years of experimentation.
I wanted something that had very low power consumption (I was already thinking
'green' many years ago...) and could connect to standard light switches.
In addition, it had to be reasonably fail safe - there is nothing worse than
adding some fancy electronics to a family house which then leaves them in darkness at
the first sign of failure.
This project meets all these requirements, in fact, unlike many commercial
timers, the idle power consumption is zero - can't get much better than that!
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Disclaimer: Whilst information on this page is given in good faith in order to help others, no responsibility for this information is assumed and all liability in respect of such information is disclaimed. |
The first part is the mains wiring itself:
This is a standard "chain" of two way switches, ending with a step relay which acts as a latching changeover switch, changing state every time the coil is pulsed. With the step relay in either state, and no other connections, the circuit will operate as a standard two way light switching circuit in that each switch can be used to turn the light on or off. All but the first switch in the chain need to be "intermediate" or X switches.
The second part of this is the timer electronics:
When the main light is on, the 47uF capacitor slowly charges via the 2M2 resistor. After about two minutes, this capacitor is charged to around 150V and the two neon lamps conduct and fire the thyristor. This discharges the 47uF capacitor through the coil of the step relay, changing it to the other state. The main light now turns off and the timer circuit is disconnected. The other neon is really just there as a safety device to remind me that there is high voltage present on the circuit.
Construction
The key component is the step relay; I used a Finder 20238230
device http://www.findernet.com/en/products/profiles.php?serie=20
This can switch up to 16A, which is more than enough for domestic
applications. I bought mine from Farnell
- they also sell the thyristor (ST) and the neon lamps.
As the relay is a DIN rail mounting device, I constructed the timer in a
small DIN
rail component case, and mounted them both in a small DIN rail box.
I suppose I should include the usual safety warning; if you are not experienced
working with several hundred volts of electricity, please don't attempt this
project, and certainly don't send me your medical bill if you fry yourself!
The total cost of the parts for this is under £30, including the case.
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Disclaimer: Whilst information on this page is given in good faith in order to help others, no responsibility for this information is assumed and all liability in respect of such information is disclaimed. |