How to Keep LED On for 1 Hour with Switch Activation—Simple Timer Circuit Ideas

423 14

#1 21680128 27 Jun 2018 02:59

Jason Lukacsko Jason Lukacsko

Anonymous

Post #1
21680128 27 Jun 2018 02:59

Not an EE but an Industrial Designer. I need a LED to be turned on via a switch and remain on for 1 hour. What would be the best approach to accomplish this? Thanks in advance
ADVERTISEMENT
#2 21680129 27 Jun 2018 07:26

David Ashton David Ashton

Anonymous

Post #2
21680129 27 Jun 2018 07:26

Jason, sorry, not enough information here. What power do you have available? When you say an hour, do you want precisely one hour or would something that does within a few minutes be OK?There's an integrated circuit called a 555 that would do this for you, but not very precisely, even if you put in an adjustment.If you have mains power available, you could time it more precisely by counting the cycles of the mains 50/60 Hz power.Which approach you would take depends on your requirements and resources....
#3 21680130 27 Jun 2018 18:15

Rick Curl Rick Curl

Anonymous

Post #3
21680130 27 Jun 2018 18:15

Hi Jason-I'd start by taking a look at TI's TPL5111 system timer. It can generate delays between 100 milliseconds and 7200 seconds, and it's pretty easy to use. It operates on 1.8 to 5 volts, so you'll need a source of voltage to run the chip and if the LED needs to be very bright you'll need to add an interface circuit (probably a single transistor) to increase the chip's output capability.If you want to provide more information about what you want to do we can offer more help.Edit: You might also take a look at the 74HCT555 chip.
-Rick
#4 21680131 27 Jun 2018 20:05

Jason Lukacsko Jason Lukacsko

Anonymous

Post #4
21680131 27 Jun 2018 20:05

Here is more info. The space this needs to occupy is small, imagine an area 2.5" diameter and hopefully no more than 0.5" tall. It will need to be battery operated and the LED will be the source for a light pipe that will illuminate the outer edge of a 2.5" acrylic disc.
Exactly an hour would be nice in order to make that claim on the product (don't want to run into the whole Subway foot long sub not being actually 12" lawsuit) but if its easier to get within a few minutes that should be acceptable
ADVERTISEMENT
#5 21680132 27 Jun 2018 20:40

Jason Lukacsko Jason Lukacsko

Anonymous

Post #5
21680132 27 Jun 2018 20:40

I created this circuit to show a proof of concept. The LED will fade away after about 2 minutes . Could this approach be used to stay on for an hour? Parts list include BC 547 Transistor, 2200uF Capacitor and 47 and 150k Ohm resistors
#6 21680133 27 Jun 2018 21:12

Aubrey Kagan Aubrey Kagan

Anonymous

Post #6
21680133 27 Jun 2018 21:12

Jason
There are quite a few details omitted from your question. How accurate do you want the time period? Do you want it to be retriggerable? What is the operating voltage? Is it a freestanding LED and is it configured with a resistor etc. Where do you want to use it? Do you want to make it yourself, and have you got the experience.I am going to take a different tack to my colleagues above, and assume that you want it for a process outside of a hobby interest and that you are not interested in producing a simple prototype. You can get timer relays which can solve your problem without too much concern about the internal workings. There are many such devices and suppliers- you might want to start at Digikey, which is where many designers do- see this page
#7 21680134 27 Jun 2018 21:20

Max Maxfield Max Maxfield

Anonymous

Post #7
21680134 27 Jun 2018 21:20

Hi Jason -- I agree with the earlier answers -- we need a bit more information -- you say "I need a LED to be turned on via a switch and remain on for 1 hour. What would be the best approach to accomplish this?"When you say "switch," do you mean a toggle switch -- something like a light switch in a house -- or do you mean a momentary push-button switch?Assuming a toggle switch, starting from an OFF condition, does flicking the switch ON cause the LED to come ON? When does the 1 hour delay start? I mean, does it start when the toggle switch is turned ON, or when it's turned OFF again.Suppose someone turns the toggle switch on and leaves it on for 2 hours -- does the LED also stay on for 2 hours, or does it turn off after 1 hour, or does it stay in for 1 hour after the switch has turned off?Suppose someone turns the toggle switch On and Off again and the LED turns On -- now suppose that after 30 minutes the switch is again turned On and Off -- does the LED still go off in 30 minutes time, or does the 1 hour count restart from the second toggle of the switch?How accurate do you need the 1 hour delay? Would +/- 10 seconds be OK, or +/- 1 second, or does it have to be accurate to a millionth of a second?
Sorry -- I R an Engineer LOL
ADVERTISEMENT
#8 21680135 28 Jun 2018 17:42

Aubrey Kagan Aubrey Kagan

Anonymous

Post #8
21680135 28 Jun 2018 17:42

I would suggest using one of those 8 pin super cheap micros, Microchip comes to mind. Depending on you battery voltage and capacity you could get away with just the 8 pin IC. One decoupling capacitor is the only extra component (plus of course the LED and resistor). Time is then set up via software based on the internal oscillator so there is no issue with getting to 1 hour.
Thinking about it you may need a voltage regulator to keep the intensity of the LED constant.
#9 21680136 28 Jun 2018 21:10

Justin Spencer Mamaradlo Justin Spencer Mama...

Anonymous

Post #9
21680136 28 Jun 2018 21:10

You can use a mechanical switch (like a relay) - the one that springs back to its original position after an hour. Quite inaccurate, but it's the simplest implementation for inexact purposes. Hehehe...
#10 21680137 29 Jun 2018 00:51

Elizabeth Simon Elizabeth Simon

Anonymous

Post #10
21680137 29 Jun 2018 00:51

I don't think this approach will work for an hour. At least not without a much bigger capacitor that won't fir in your size constraint.Your circuit works by having the switch charge the capacitor then the capacitor is discharged by the LED.
It looks like you have 3V to work with. If you have an LED that requires 2.5V (check the data sheet), the LED will go out when the capacitor voltage drops 0.5V (actually less due to the resistor). If the current through the LED (set by the resistor) is 10mA, we can get a rough estimate of the capacitor size needed by C = 10mA * (3600 sec) / (0.5V) which gives me 72 Farads if I did that right.I think a timer relay or small 8-pin super cheap micro as Aubrey suggested is probably the best bet.
#11 21680138 29 Jun 2018 03:26

David Ashton David Ashton

Anonymous

Post #11
21680138 29 Jun 2018 03:26

I was thinking about this after my post above and while a 555 is quick and easy and does not involve any programming, getting a reliable 1 hour delay would need a very high resistor (22Meg) and capacitor (up to 1000 uF) and any leakage in the capacitor would render the results erratic or unusable.So I came to the same conclusion as Aubrey above (he is a smart guy and beat me to it!). The only thing I would add is that if you can't program in C or assembler you could consider the PICAXE chips. They are programmed in BASIC which you may already know, are cheap and easy to use. Their smallest chip, the 8-pin 08M2, would easily do what you need. I've played with these chips and they are really easy to use.You can get a kit with a PICAXE 08m2, PCB, LEDs and switches, battery box, that would get you started for a proof-of-concept, and you could then fit the result into your case using a smaller PCB or even veroboard. The only other thing you'd need is a programming lead.I wrote some articles some time ago on my journey with the PICAXE chips:Part 1 , Part 2 , Part 3 , Part 4 .
ADVERTISEMENT
#12 21680139 29 Jun 2018 15:15

Sean Ellis Sean Ellis

Anonymous

Post #12
21680139 29 Jun 2018 15:15

Having to program a PIC seems like overkill. Here's a circuit I found by putting "counter timer IC 1 hour" into Google:
http://www.electronicecircuits.com/electronic...uits/cd4060-timer-circuit-1-minute-to-2-hours
#13 21680140 29 Jun 2018 16:48

David Ashton David Ashton

Anonymous

Post #13
21680140 29 Jun 2018 16:48

Nice call Sean...the circuit as shown would need some mods to act as a monostable I think, but should be doable.
#14 21680141 29 Jun 2018 19:42

Jason Lukacsko Jason Lukacsko

Anonymous

Post #14
21680141 29 Jun 2018 19:42

Thanks everyone, your help has been much appreciated.
#15 21680142 30 Jun 2018 09:54

Richard Gabric Richard Gabric

Anonymous

Post #15
21680142 30 Jun 2018 09:54

CD4541 can be used as well, cheers,Richard
Create an account, log in here. You will receive points by participating in discussions.
Join this discussion.

Install Elektroda application

Didn't find an answer? Ask Artificial Intelligence

*I agree to send the question to OpenAI, Anthropic PBC, Perplexity AI, Inc., Kagi Inc., Google LLC - owners of language models in order to prepare the best response. The companies may monitor and log information entered into the form.

*I agree to publicly display my question and answer. The question and answer will be publicly available to everyone. The process may take a few minutes. Upon completion, you will be redirected to the page with the answer.

Wait...(2min)

Topic summary

✨ The discussion addresses how to keep an LED illuminated for one hour after activation by a switch, focusing on a compact, battery-operated design with a 2.5" diameter and 0.5" height constraint. Various timing approaches are considered, including analog and digital solutions. The 555 timer IC is suggested for simple timing but lacks precision and requires large resistor and capacitor values for hour-long delays, which may be impractical due to size and leakage issues. Counting mains power cycles is mentioned but not applicable for battery operation. Digital microcontrollers, such as low-pin-count Microchip PIC or PICAXE microcontrollers, offer precise timing with minimal components and programmability, suitable for the size and power constraints. Timer ICs like the Texas Instruments TPL5111 system timer and CMOS counters such as CD4060 and CD4541 are proposed as alternatives for adjustable delays without complex programming. Mechanical relay timers are noted as simple but inaccurate. The importance of clarifying switch type (toggle or momentary), retriggerability, and timing accuracy is emphasized. Battery voltage and LED current requirements influence component selection, with suggestions to use transistor interfaces for higher LED brightness and voltage regulators for consistent illumination. Overall, microcontroller-based timing is favored for accuracy and compactness, while analog and relay solutions are less practical for a precise one-hour LED activation in a small, battery-powered device.
Generated by the language model.

FAQ

TL;DR: For a one‑hour LED timer in a small, battery‑powered build, use TI’s TPL5111 ("generate delays between 100 milliseconds and 7200 seconds") or a tiny 8‑pin micro; 555 RC is imprecise for 1 hour. [Elektroda, Rick, post #21680130]

Why it matters: This FAQ helps makers pick a reliable, compact 60‑minute LED‑on solution without trial‑and‑error.

Quick Facts

Space target: Approx. 2.5 in diameter, ≤0.5 in tall; battery‑powered light‑pipe LED use case. [Elektroda, Anonymous, post #21680131]
TPL5111 delay range: 0.1–7200 s on 1.8–5 V; add a transistor for higher LED current. [Elektroda, Rick, post #21680130]
Pure RC approach estimate: ~72 F for 10 mA over ~0.5 V droop to reach 1 hour. [Elektroda, Anonymous, post #21680137]
555 for 1 hour needs ~22 MΩ and up to 1000 µF; leakage makes timing erratic. [Elektroda, Anonymous, post #21680138]
Alternative counter timers to explore: CD4060 and CD4541 for long delays. [Elektroda, Anonymous, post #21680139]

What’s the simplest way to keep an LED on for about 1 hour?

Use a low‑power timer IC or an 8‑pin microcontroller. TPL5111 covers up to 7200 s on 1.8–5 V. Add a small NPN transistor if the LED needs more current than the timer pin can source. This approach fits tight spaces and keeps time well enough for a product claim. A pure RC fade is not practical for 60 minutes in your size. [Elektroda, Rick, post #21680130]

Will a single big capacitor keep an LED on for an hour?

Not realistically here. At 3 V supply and ~10 mA LED current, a rough calculation shows about 72 farads for a 0.5 V drop. That’s a supercapacitor class part and won’t fit a 0.5‑inch‑tall puck with other electronics. It also won’t hold constant brightness. [Elektroda, Anonymous, post #21680137]

Can a 555 timer do a precise 1‑hour delay?

It can, but not precisely or reliably in this use. Achieving ~3600 s needs ~22 MΩ and up to 1000 µF. Capacitor leakage and tolerance drift make the result erratic. As one expert notes, the 555 is “not very precisely” suited for long delays. [Elektroda, Anonymous, post #21680138]

What is the TPL5111 system timer and why use it?

TPL5111 is a low‑power system timer IC from TI that generates programmable delays from 100 ms to 7200 s on 1.8–5 V. It’s easy to use and ideal for battery builds. Use a transistor interface if your LED requires higher current or constant brightness. [Elektroda, Rick, post #21680130]

How do I build a 1‑hour LED timer with TPL5111?

Power the TPL5111 from your battery (1.8–5 V) and set its delay for 3600 s.
Drive a small NPN transistor from the TPL5111 output; size the LED resistor for your brightness.
Wire the user switch to start the cycle and route LED power through the transistor. [Elektroda, Rick, post #21680130]

What about using a tiny 8‑pin microcontroller?

An 8‑pin Microchip PIC can time one hour using its internal oscillator and simple code. You add one decoupling cap, the LED, and a resistor. Consider a regulator if you want constant LED brightness as the battery sags. This keeps parts count and size very low. [Elektroda, Anonymous, post #21680135]

What is PICAXE, and can it do this easily?

PICAXE is a beginner‑friendly microcontroller platform programmed in BASIC. The 08M2 8‑pin device can time 1 hour and drive an LED with minimal parts. It’s cheap, easy to program, and suitable for quick proof‑of‑concept builds and small enclosures. [Elektroda, Anonymous, post #21680138]

Are CD4060 or CD4541 better for 1‑hour timing?

Yes, both are long‑delay timer/counter ICs. CD4060 provides an oscillator with divider stages, while CD4541 is a programmable timer. With the right RC and wiring, they can deliver a one‑shot around 1 hour in a compact board. “Nice call… doable.” [Elektroda, Anonymous, post #21680139]

I need battery power and a small enclosure; what should I watch?

Choose low‑power timing and avoid large RC values. The enclosure is about 2.5 inches in diameter and 0.5 inches tall. That rules out supercaps and bulky relays. Favor TPL5111 or an 8‑pin micro, plus a small transistor for LED drive. [Elektroda, Anonymous, post #21680131]

Do I need a transistor to drive a bright LED?

Often yes. Timer outputs source limited current. Use a single NPN transistor to switch the LED current set by a resistor. This keeps the timer happy and maintains brightness over the hour. It also preserves timing accuracy by reducing output loading. [Elektroda, Rick, post #21680130]

Should the timer retrigger if the switch is toggled again?

Decide behavior up front. Define whether a second toggle restarts the 1‑hour count or is ignored. Engineers recommend clarifying switch type, start conditions, and retrigger logic before choosing parts or code. This avoids surprises in user tests. [Elektroda, Anonymous, post #21680134]

Toggle vs. push‑button: when should the hour start?

Specify this in your design. With a toggle, start timing when turned ON, or when turned OFF after arming. With a push‑button, start at press or release. Document these rules so your circuit or code implements the correct user experience. [Elektroda, Anonymous, post #21680134]

Can I use mains frequency to keep one hour very accurate?

Yes, counting 50/60 Hz cycles gives accurate timing. However, this project is battery‑powered and space‑limited, so mains is impractical here. Keep this option in mind for mains‑powered products that demand tighter accuracy without crystals. [Elektroda, Anonymous, post #21680129]

Is a spring‑return mechanical timer switch viable?

It works for rough timing, but it’s bulky and inaccurate for a 0.5‑inch‑tall puck. Mechanical options suit low‑precision tasks. For product‑grade one‑hour timing, prefer IC‑based solutions with defined tolerances and compact footprints. [Elektroda, Anonymous, post #21680136]

Any gotchas that can break a 1‑hour design?

Watch electrolytic leakage and tolerance in large RC networks. They drift and shorten or lengthen the delay. Battery droop also dims LEDs unless you regulate or PWM. As one poster put it, large‑value 555 timing can become “erratic or unusable.” [Elektroda, Anonymous, post #21680138]

Generated by the language model.