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Timed LED Light Circuit

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roadrunnerjohn

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Hello,

I am building a toy wooden truck and would like to build a circuit that would allow my child to press a button and have headlights (LED's) turn on, and then turn off automatically after about 30 seconds. I can't even seem to work out what type of circuit this is called. If someone knows of one or could design one for me I would really appreciate it.

Thanks so much,

John
 
High Beams

John,

Here is a circuit that should do it. You should be able to get all the parts at Radio Shack. Keep in touch if you have any questions.
 

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Thanks guys! RonV, I'm sorry for my ignorance but a question about the triangles in your diagram that come off from the capacitors, push button switch and LED's. Do these just represent joining those parts back to the negitive of the 9V? I see that D1 and D2 are the LED's, so what does the symbol of the rectangle with a triangle end enclosing "LEDS" mean? Where would this join up to?

Once again, thanks so much,

John
 
Thanks AtomSoft, so I did have it right. Do you happen to know what the "LEDS" box in the right hand bottom corner is for? It looks to me as though D1 an D2 are the LED's. So I'm not sure what to do with this.

Thanks,

John
 
Thanks AtomSoft, so I did have it right. Do you happen to know what the "LEDS" box in the right hand bottom corner is for? It looks to me as though D1 an D2 are the LED's. So I'm not sure what to do with this.

Thanks,

John

That is just the way that RonV labeled the electrical node which is connected to pin 3 of the 555 and the Leds. Think of the "dog-house-laying-on-its-side" as an electrical terminal. It has the name "LEDS". It is used to reference an electrical node so that it can be plotted in the plot-pane. Look at the red trace "V(leds)". Note that one end of the switch is named "SW", but without the dog-house. It is also plotted as the green trace, v(sw).
 
That is just the way that RonV labeled the electrical node which is connected to pin 3 of the 555 and the Leds. Think of the "dog-house-laying-on-its-side" as an electrical terminal. It has the name "LEDS". It is used to reference an electrical node so that it can be plotted in the plot-pane. Look at the red trace "V(leds)". Note that one end of the switch is named "SW", but without the dog-house. It is also plotted as the green trace, v(sw).

wow that confused me mike heh

It would be simpler to say:

Thats just a label. Its there to show you the name of the wire and what its for.. for example if you have more than 2 leds in series you connect the rest of them to that line(wire)... (and for simulator purpose)
 
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English is not my native language, heh!

There are two independent things here; one is "naming an electrical node (wire)", the other is adding a "port" (pin, terminal). You can do one without the other.
 
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Here are several tricks: Note the use of a real switch (instead of a voltage source). Note the use of a Page connector (node SW). Note that the traces are much more readable when posted here.

Note that the plot shows "n002" (dark blue). Which node is n002?
 

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Since this is battery powered, I would assume he wants a circuit that draws very little power when the LEDs are not lit. That is not the case for a standard NE555, which would discharge an AA battery in less than a month (or a 9V alkaline in less than a week).

The CMOS version, such as the LMC555 takes significantly less current, so AA cells should last over a year (even with the occasional LED current draw). Since the CMOS version has a lower output drive than the standard 555, it may require an added transistor on the output to drive the LEDs.

Edit: Even better would be the use of a CMOS multivibrator such as the CD4047B, which has a maximum quiescent current of only a microamp or so. Thus the battery life would be essentially determined by how often the LEDs were lit. It may also need an added transistor on the output to drive the LEDs.
 
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Hello,

I am building a toy wooden truck and would like to build a circuit that would allow my child to press a button and have headlights (LED's) turn on, and then turn off automatically after about 30 seconds. I can't even seem to work out what type of circuit this is called. If someone knows of one or could design one for me I would really appreciate it.

Thanks so much,

John

hobbyists do love their antiques! 74HC14 takes 2uA https://www.electro-tech-online.com/custompdfs/2010/08/sn74hc14.pdf a CMOS 555 takes 90uA https://www.st.com/stonline/products/literature/ds/4077/ts555.pdf. on the input a momentary switch charges a capacitor that a resistor discharges. the output drives the LEDs.
 
Hello everyone! Thanks so much for all your input. Yes, AtomSoft, your explanation was definitely easier to understand for a novice like me.

Just to clarify, I'm happy to use either 9v or AA's and seeing as my son is extremely, enthusiastically wanting lights, I imagine they'll get a fair bit of use. Hence me wanting a circuit that turns off automatically. So what every you guys think would work best, I'm up for. I'd really appreciate someone drawing me a circuit which contains either the CMOS or the CMOS Multivibrator, as the idea of my batteries lasting only a week worries me.

Regards,

John (and Roadrunner Junior)
 
Hello everyone! Thanks so much for all your input. Yes, AtomSoft, your explanation was definitely easier to understand for a novice like me.

Just to clarify, I'm happy to use either 9v or AA's and seeing as my son is extremely, enthusiastically wanting lights, I imagine they'll get a fair bit of use. Hence me wanting a circuit that turns off automatically. So what every you guys think would work best, I'm up for. I'd really appreciate someone drawing me a circuit which contains either the CMOS or the CMOS Multivibrator, as the idea of my batteries lasting only a week worries me.

Regards,

John (and Roadrunner Junior)

how much space do you have for batteries and such?
 
I would recommend a PIC micro... a small 16F (cheapest you can find) any PIC will be able to do this. Get a 12F and it will do it... You can then have a sleep timer and have a interrupt wake it up. Batteries will lasts months or a year or so heh... and would only require 2-3AAA or 2-3AA batteries to operate...
 
Much simpler Delayed LED turn off with almost zero power consumption after the LEDs turn off.
If battery size is an issue, you could use one of these
 

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16F683 @ FOSC = 32khz uses 28uA
4 Leds in parallel = 20mA * 4 = 80mA

Now the PIC + Leds = 80.028mA

Batteries 2500mAh

LIGHTS ON ALL THE TIME WOULD DRAIN IN 31 HOURS (1 day 7 hours)
PIC ONLY with lights off would last 89,285 HOURS (at least 10 Years)


Depends on how much it played with heh

If he plays 3 hours a day with it, thats about 240mA a Day...It will last 10 Days.. without needing a new battery...
1 hour a day would be 80mA ... would need new batteries in about 31 days. or 1 time a month
 
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