Blinking Nightlight (by request)

Instructables user Pagemaker provided a link to a generic blinking circuit using a 555 timer, and requested info on how to incorporate a photoresistor to enable the circuit to turn off in daylight. In addition, Pagemaker wanted to use more that one LED. His original posting is HERE. This instructable will show you how to do just that.

Step 1 Looking at the initial 555 circuit

The first step in creating the blinking nightlight was to analyze the original circuit, which can be found here.

There are a number of websites that will teach you everything you need to know about 555 timers, so I'll leave that to others. Here are a two of my personal favorite sites on 555 timers that will get you started:

http://www.uoguelph.ca/~antoon/gadgets/555/555.html

http://home.maine.rr.com/randylinscott/learn.htm

Basically, depending on what external components (resistors and capacitors) we use, we can change the rate of blinking.

Comments

[nodoubtman]

What transistor??

[mhkabir]

can I use it with a 12v power supply and 30 - 40 LEDS?

[stuuf]

You seem to have the LEDs in your schematic wrong. I was wondering how they would light up reverse biased like that; the circuit you linked to has the cathode connected to the discharge pin. How much current can the discharge pin sink? I know that the 555 usually can only handle a small amount of current on its output pin, so an external transistor is needed for driving a lot of LEDs, but how many can it drive in this configuration?

[inventorjack]

Thanks again for the correction. It's been fixed.

[skantu]

Mate Jack, I loved your circuit but , and i just have a small doubt, i think it will be easy far you to answer, im using what you done, but im trying to make it blink once a second (like turn lights on a car), you wrote.. “Basically, depending on what external components (resistors and capacitors) we use, we can change the rate of blinking.“ So could you please help me to decide which (capacitor or resistor) to change to make it blink faster? .. i will really appreciate it. Thanks mate.

[inventorjack]

Thanks for the catch on the LEDs. I've got to go to work today, but when I get back home, I'll fix the schematic. Not sure how I managed to screw up the orientation there :( Regarding the source/sink of the TLC555, the nominal parameters for this chip are 10mA Source and 100mA Sink, but it can operate up to 100mA Source. A better choice for the 555 timer would be the SA555, which can both source and sink up to 200mA, allowing a bit more flexibility in our design. I stuck with the TLC555 in the writeup, because that was the one originally used, and it provide enough current for the 4 LEDs, but not much more than that.

[hominid]

Thank you Inventor Jack for this. It gives good information and a useful "apatite wetter" for u C's.

[hominid]

I forgot to mention I want to make a flasher for my cat "Gerald" so I can see where he is lurking in the shadows at night. We keep him inside at night to help protect the wild life. We live in inner Melbourne city, but you still get those deadly brown snakes in the street lanes. Never far from the wild in Australia!

[sentinel0]

what would the resistor values be if I used a 9v battery instead?

[twenglish1]

this would be a ton easier with a small microcontroller

[inventorjack]

Don't get me wrong, uC's are awesome. I play with them all the time. But sometimes it can be much more satisfying to work through a problem without resorting to the microcontroller. Also, many people don't have a programmer or the experience to use one. There's also the argument that using a micro to blink a few LEDs is like using a slegehammer to pound a tack. Why throw so much unneeded power at a simple problem? Hope none of this sounds offensive. I just don't understand why many people choose the micro as their first choice in most everything electornics-related. Use the right tool for the right job/situation.

[twenglish1]

its not offensive but i have done alot with other electronic devices and im learning how to use microcontrollers. if you want to get started with microcontrollers read this instructibleit tells you how to build a programmer and use it for pretty much free the only thing thats not free is the microcontroller but you might be able to find a free sample somewhere and it shows you how to make a LED blink

[Pagemaker]

I really appreciate you doing this. I'm going to order some parts and try to get it going. Couple of questions... what resistor value would you use to make it blink twice per second? and does this circuit draw power when its light? Also, how hard would it be to make the same circuit that would make use of rechargeable batteries and a solar panel to charge in the daytime? Thanks again...

[rappa]

Thanks for the write up. I have been interested in a doing something like an led throwie, but turns on at night and blinks to conserve power. It would be helpful to see the entire circuit (with photoresistor and npn).

[inventorjack]

I added an image in the last step which labels each component for easier identification. Hope that helps. Also, in step 4, the second image shows the entire schematic.