# Super Simple Circuit questions

Discussion in 'Circuit Help' started by Jacob Johnson, Jan 4, 2017.

1. ### Jacob Johnson

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Yes, I'm a noob. I just need a couple answers that I can't seem to find otherwise.
I'm trying to make a really simple and cheap (focus on quantity) circuit to turn on LEDs for a set period of time at the press of a momentary switch (push button, lights light up for 3 minutes or so, then turn themselves off).
So I need to know what I need to purchase, and how to put it together.

Jacob Johnson, Jan 4, 2017

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You need a retriggerable monostable, these can be easily made using standard logic gates and some timing components such as resistors and capacitors, you should be able to find lots of circuits on Google.
Thanks

Arouse1973, Jan 4, 2017

3. ### Herschel Peeler

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Retriggerable? Why?
LM555 is okay and cheap.
Battery powered?
What LED did you have in mind?
Here's a starting point. With a 390K timing resistor I get about 2 1/2 minutes. With a 430K I get about 3 1/2 minutes. Specifics depend mostly on how close your 470 uF cap is.
Total cost for parts shown comes to less than \$1.00.

(P.S. After playing with the circuit, the diode is not needed. Replace it with a wire.)

Last edited: Jan 5, 2017
Herschel Peeler, Jan 5, 2017
Jacob Johnson, davenn and Harald Kapp like this.
4. ### Jacob Johnson

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Hey, thanks. At the very least, I can use your diagram.
So, I'm afraid I might not have been clear enough when I said I'm a "noob". I have minimal knowledge, at best, of electronics. I recognize a couple symbols in the diagram (resistors, capacitors, diodes, switch, and ground), but overall, it's really over my head (mostly your numbers). :/
I'm looking for a very simple and small circuit for about five or six small LEDs. With enough battery power to light them at full capacity for a good amount of time (many many cycles of approx. 3 mins)
It's possible I might be able to figure out what to do with your diagram (with help from my brother), so that's a great start. I appreciate the help.
Any further clarification would also be appreciated.

just which parts I need (exactly what to search for) and in what quantities. Aside from that, I'll figure it out.

Thanks, again,
Jacob Johnson

PS: Also thank you to Arouse for trying to help, but unfortunately, half your reply went directly over my head, and the rest was meaningless without the part I didn't understand. :/

Jacob Johnson, Jan 5, 2017
5. ### Jacob Johnson

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Oh, I should probably add that the circuit should be very compact and self-contained (ie: portable and completely encased)

Jacob Johnson, Jan 5, 2017
6. ### Harald KappModeratorModerator

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Get a kit like this or like that?
Build it into a case of your own design.

Harald Kapp, Jan 5, 2017
7. ### Jacob Johnson

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Idk, that seems a bit pricey for my propose. :/
Herschel's option seems more reasonable at a mere buck a pop. While those kits would greatly simplify the project (rather make it easier for me to do), I'm afraid it would turn out far too expensive, and tbh, those circuits seem a little excessive (I'm certainly no expert, but I don't think my circuit should require that many components (or maybe it just looks like more because of the green boards)).
Thank you, tho.

Last edited: Jan 5, 2017
Jacob Johnson, Jan 5, 2017
8. ### Jacob Johnson

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I apologize if, by being so naive as I am, I am misusing the forums.
I would be asking a person like at an electronics store, but there aren't any out where I live. :/

Jacob Johnson, Jan 5, 2017
9. ### Harald KappModeratorModerator

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If a kit is too expensive, you'll have to put up the circuit by yourself. See this example for example.

You don't that's what we're here for. Only it's a bit difficult if on the one hand you don't want to spend the money for a kit but don't understand Herschel's schematic on the other hand.

For more than one LED the schematic needs to be modified. You may have to add a driver to power the many LEDs.
What battery voltage are you goinf to use? This makes a difference. With a low battery voltage, you will have to put the LEDs in parallel, each with its own current limiting resistor, bu the total current will be comparatively high.
With a high battery voltage you may be able to put the LEDs (or at least some of them) in series with only one current limiting resistor. The total current will be less.
Power will be the same in both cases.

For more detailed help we need more parameters:
- operating voltage
- type of LED (diffferent LED types have different operating voltages)
- current per LED (depends on teh type, too)

Harald Kapp, Jan 5, 2017
10. ### Herschel Peeler

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Next step then. Attached is a data sheet for the LM555. It can be configured to create a string of pulses or a single pulse. Shown is the basic single pulse deign. Timing is controlled by the 470 uF capacitor and the 390K resistor. Pin 3 is the output. It goes high when the trigger input is taken low. How long it stays high depends on the R and C mentioned.
The output can drive over 100 mA high or low. So it can drive lots of LEDs.
For lower power there is also an 7555 that is CMOS. Same pin out and function but can't drive as much output current.
You can usually pick up the 555 for \$0.50 or less. It has been around a long time and is really popular.
Battery powered? What voltage? The circuit provided would work fine down to about 4.5 V, up to 15 V.
Three AA or AAA batteries should last a long time, especially if you used the 7555.
How many and what kind of LEDs? I built it using a white LED, maybe 15,000 mcd (pretty bright).
No component values are critical.

#### Attached Files:

• ###### LM555 d.pdf
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Herschel Peeler, Jan 5, 2017
11. ### AnalogKid

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What is the project?
How many units?
How many LEDs?
How Bright?
Battery type, size, etc?
Size limit?
Cost limit?
How accurate must the 3 minute interval be?

Important: Do the LEDs have to turn off crisply, or can they fade away over 5 to 30 seconds?

Depending on the answers, this could reduce the electronics to one resistor, one capacitor, and one transistor. The problem is that 3 minutes is a loooong time for a simple R-C timer circuit of any nature, but your super-ultra-secret project requirements probably preclude a counter-based approach. At least no one has mentioned a PIC yet...

ak

AnalogKid, Jan 5, 2017
12. ### Jacob Johnson

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Okay, so now I have a better idea of what info you need. Thank you.

So I intend to have different units with different color leds (sometimes multiple colors). (idk if there's different info you need on what type, cause I know very little about leds I just need bright leds that shine constant in a specific color)
A maximum of six maybe seven.
Powered by AA batteries. up to 4, but the fewer the better. (2 is ideal, 3 is acceptable, 4 is pushing it, but prolly doable) (if 4 is going to make the circuit easier, I'll just do 4)
The brighter the leds can light the better.
It's approx 3 minutes. Really that's an arbitrary number. it could be 2 or 1.5 if it has to be.

As for the project, I thought it not necessary to say, but I guess there's more to consider than I thought there would be. :/

I'm looking into making light up shape pillows to sell on etsy. The tutorials I've seen use really cheap-a\$\$ methods that look like dollar store quality at best, which is not what I'm going for.
I'm not very well versed in the technical terms in electronics, but I usually have a working understanding. The main thing thats throwing me off is the timer. If I'm told exactly what search criteria to use to find one (or better a link), I could probably figure the rest out by a schematic. (except I don't know what the vcc is oHo)

So as for price, it just needs to be cheap enough to be able to be competitive in my resale price.

Thanks again for all the help.

Last edited: Jan 5, 2017
Jacob Johnson, Jan 5, 2017
13. ### KMoffett

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You will have to play with the R1 and C1 values for 3 minutes.

Ken

Added Note: the MOSFET should have been labeled NDP6020P for a P channel

Last edited: Jan 5, 2017
KMoffett, Jan 5, 2017
14. ### Jacob Johnson

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This looks very simple which is great for me, but a couple questions.
Will this circuit run 6 leds?
and please explain this part: http://imgur.com/yp53N9I
(cause to me, it looks like three capacitors and a diode)

Jacob Johnson, Jan 5, 2017
15. ### Jacob Johnson

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Omg, idky I didn't check that circuit earlier. That seems so simple. I can do that. The only thing is I need to know what sort of adjustments I need for the parameters I mentioned above. (ie: 6 leds, 2-3 minute timer)

PS. Now I think of it, a 9v battery would work great.

Jacob Johnson, Jan 5, 2017
16. ### AnalogKid

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Other than flipping everything over to an N-channel FET (lower Rdson per \$), Ken's circuit is exactly what I had in mind. Also, a 9 V battery significantly increases the number of MOSFETs to choose from.

ak

AnalogKid, Jan 5, 2017
17. ### KMoffett

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Jacob,

Q1 is a P-Channel MOSFET. (label should have been NDP6020P)
With 9 V you could do 6 LEDs.

AK,
That Mosfet was used for a 3V battery circuit. Changing the circuit for a N Logic level Mosfet would improve availability and cost.

Ken

Last edited: Jan 5, 2017
KMoffett, Jan 5, 2017
18. ### Jacob Johnson

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Ok, thank you. I think I've figured it out. This schematic is very helpful.

Thanks everyone for helping out so much.

--Jacob Johnson

Jacob Johnson, Jan 7, 2017
19. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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The switch across the 1uF capacitor may not like the current from the capacitor. I'd put a 100 ohm resistor in series with the switch.

(*steve*), Jan 8, 2017

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