Timed Light Switch

There are timers used to control lights when on vacation that would probably do what you want...

https://www.amazon.com/electrical-timers/b?node=495340

I would like to make my own.

It's not worth the effort when commercial versions are so readily available.

Why dual throw?

Why not: single pole, single throw, NO (1 FORM A)

(You could go for dual pole if you want to switch live and neutral.)

Go to Digikey or mouser and search for relay then filter your results 'til you get what you want:

SPST-NO

SPDT

$2 or $40 (doing dual throw with a mechanical switch is easy: you just have a central rest position, but, with a relay it gets a lot more complicated).

Oh I actually meant DPST sorry. Throw connected in parallel, one pole for the hot leg of the heat lamp and one pole for the hot leg of the UV lamp.

Why DPST. Why not tie both the UV lamp and heat lamp to the load side of an SPST switch?

I have a $5 timer from Home Depot for controlling my turtles light cycle.

I would like to make my own.

You may find it difficult to find a (5V) TTL level relay coil with enough mechanical force to close a 10-15A relay armature. There is also the back-EMF to consider as the coil is deenergized, a reverse polarity diode across the coil to protect your computer output. The drive capability of your computer output may require you have two relays, one small enough to not overload your computer output, to drive one heavy enough to switch your power circuit.

If you gang a day timer, it measures the passing of each day, with 12 hour stoppers, and wire a photocell to extend the daylight, if it gets dark before 12 hour light cycle expires. Run the timer continuously for consecutive 12 hour cycles. Turning the lights on at dusk and run them until the 12 hour stopper comes by, would that do it?

Cloudy day, the lights would run 12 hours at a time, one stopper turns them on, the other stopper turns them off. If there is plenty of light, no lamps needed, just like in the prehistoric times...

If its a 45W and 60W bulb, theres not a lot of current going thru this. The 60W itelf doesnt even go above 1 amp. I already have a flyback diode for back emf in my schematic I drew up earlier. Your last 2 paragraphs made no sense to me.

So you don’t need two relays, both loads can be fed from 1 source, without fear of overload.

Not sure why you would need computer control for this, except to perfect your personal skills. Maybe I’m making it more complex, not understanding how a simple 24 hour time switch as used for water heaters, would not be the easiest solution. I don’t understand how the lights could be on for 16 hours as you said, under those conditions, except if outside & natural light were considered. On days where there is less daylight than 12 hours, your outdoor light control would turn on, and give you light for the 12 hour balance. That’s the design of the 12 hour clock and photocell.

Maybe there is no outside light, then the 12 hour timer will work, I don’t then understand how you could get 16 hours of light, then?

The birds are keeping me up all night, I need sleep....

Look my beard is turning blue....I'm a blue beard now...

Time to go shoppin' boss....

Oh wow, that's amazing! I'm guessing that's yours?

If you are capable of designing the circuit I would think you are capable of picking a good relay?

It seems very redundant but why not attach a relay to a vacation timer and use it like a contactor switch. Bam circuit designed.

My turtles are wintering outside in a pond I dug last spring.

Actually I had one big turtle but when the pond showed up so did another turtle.

The 70+ gallon aquarium was getting a little tight for the old girl.

Fingers crossed.. it will be very exciting to see them in the spring.

the pond has mostly frozen over but one day it hit 50 and my big turtle climbed out onto her rock for some quick sun.

At the bottom of the pond there is a circulator pump a bubble stone and a 250 watt submersible heater.

The tank is now more fishy than ever.

Not a joke... Pehaps place a proximity or micro-switch in one area of the cage with the idea of enabling the critters to chose their own On/Off times. Of course a human operaed manual and/or auto timer switch could be wired in parallel...(learning curve may vary.)

I’m not sure if the dragon would be able to learn how to do that. He’ll probably end up having some existential crisis seeing he can control his world haha.

do a search for something like an Arduino and a plug in shield (board) with relays or if you are designing your own use a driver transistor to fire the larger relays...

I’m not a big fan of the arduino. It takes away the beauty of having to design the pcb from scratch and figuring out the correct components. And yeah good idea, I’ll probably end up using some MOSFET for the switching.

The processor used in Arduino is available $2< use "dead bug" construction or build your own PCB...

Right again

Ahhhh. Reminds me of my days doing automatic gates.