LED Power Supply

Thread Starter

james c

Joined Mar 12, 2012
8
I need to run 4 slow flashing LED lights, one on each side of the house, as alarm on indicators. The power supply will be solar. I want 5mm diffused , red led's slow flashing like once every 2 sec. Any suggestions how I should do this? and if so, I need a schematic diagram. The power supply will be in the attic and runs to the leds from the power supply will be (2) at 25' and (2) at 35' .
 

BobTPH

Joined Jun 5, 2013
4,054
Why a separate power supply? Typically, an “alarm on” indicator would be powered by the supply of the alarm.

Bob
 

Dodgydave

Joined Jun 22, 2012
10,095
Use a 555 timer for simplicity, like this, alter R2 for speed control.

you can buffer the output by using an extra transistor, i would use one psu say 9 to 12V and run all the led feeds in parallel with a 1K resistor in series with each led.

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Thread Starter

james c

Joined Mar 12, 2012
8
So I could use a 12 volt solar power supply w/ battery. Do you know what value resister for R2 that would give a flash every 2 sec?
 

Wolframore

Joined Jan 21, 2019
2,410
All very good suggestions, do yourself a favor and use an LMC555 which requires less current and give you longer life between charges.
 

Tonyr1084

Joined Sep 24, 2015
6,465
What type LEDs should I use. Voltage etc?
LED's don't come in voltage they come in amperage. The typical LED you're talking about, a 5mm LED (red for example) typically has a forward voltage drop of about 2 volts and generally runs between 5 and 20 milli amps. They can be run as high as 30mA but then they don't last as long. But flashing once every two seconds isn't going to be much of a drain on the lifespan of an LED. 30mA would be about as bright as you would want to go. However, LED's are current devices. You calculate for that by starting with the supply voltage. Let's assume it's 9 volts. A single red LED will drop 2 volts, so now we are dealing with 7 volts. Assume you want 20mA. 7V ÷ 20mA = 350Ω. That's the size resistor you would want if the supply was 9 volts and you desired 20mA brightness, which is plenty bright.
BobTPH said
Typically, an “alarm on” indicator would be powered by the supply of the alarm.
That's 100% true.
...that is if it is a real alarm.
So I'm going to go along with that idea - that this isn't a real alarm system, just an attempt at a theft deterrent. Why would anyone want an alarm indicator on all four sides of the house unless he wanted someone to THINK there's an active alarm? So what happens if the system fails? A would-be thief would then think the alarm is not active and would invite them to break in.

Gotta look at all the possibilities.

When I installed alarms the only alarm active indicator was typically on the keypad. Signs could be posted in the yard warning of a system, but then some of those signs look like spoof signs and would tell a would-be thief you have something to protect but are not actively protecting it. Only a well known sign such as an ADT, Brinks or Vivint or the likes would LOOK like the real thing. But those companies aren't in business to sell signs. If you WANT their sign you have to buy their system. Otherwise you're inviting trouble.
 

Thread Starter

james c

Joined Mar 12, 2012
8
All very good suggestions, do yourself a favor and use an LMC555 which requires less current and give you longer life between charges.
Wolframore, I have decided to use a small solar panel and 3.7 volt solar charger and battery that way the unit will work when the power goes out. I have looked at the DigiKey LMC555 and am unsure which one is best for my needs. And with the voltage being 3.9 instead of 9v shown in the schematic above, can you assist with a schematic that will work? I thought about using this Solar Lamp Controller 3.7V Solar Lantern Lamp Control Board Photo-Induction Circuit Board with Switch from EBay for 6 bucks.
 

Thread Starter

james c

Joined Mar 12, 2012
8
Can somebody help me with the last part of this circuit. I am ready to build but have a solar powered addition. I have decided to use a small solar panel (5w was smallest unless I use one or two small solar walkway light solar panel) and 3.7 volt solar charger and battery that way the unit will work when the power goes out. I have looked at the DigiKey LMC555 and am unsure which one is best for my needs. And with the voltage being 3.7 instead of 9 shown in the schematic above, can you assist with a schematic that will work? I thought about using this Solar Lamp Controller 3.7V Solar Lantern Lamp Control Board Photo-Induction Circuit Board with Switch from EBay for 6 bucks.
 
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