Possible to insert capacitor between voltage source and output to delay the output? [closed]

I'm a newbie at this stuff but basically I have a 3.5v coin battery connected to a tiny switch that turns on a tiny buzzer.

What I want to do is delay the power going to the buzzer by about 30 seconds.

Would simply putting a micro capacitor between the voltage and buzzer be a way to do this? I need to keep the weight of this contraption as low as possible so that it doesn't weigh much more than the battery itself.

I tried messing around with various circuit designers but all I came up with was artistic doodles...

• No, this would not work. The easiest and lightest way to do this would probably be a tiny circuit board with an attiny or something on it in conjunction with some sort of switch, probably a single FET or BJT, but I can't be bothered to work out all the details right now. Commented Sep 27, 2019 at 20:35
• What happens after that? Do you want the buzzer to keep running until the battery dies? This sounds somewhat like a practical joke I put in a friends car once: it used a 555 timer to trigger a buzzer for 500ms every 5 minutes. Commented Sep 27, 2019 at 20:59
• If you did add a cap to delay power up, it would be very large, it would also make it so the device would not power down Commented Sep 27, 2019 at 21:06
• What’s so hard about a 33Meg R to FET gate and 1~2uF plastic cap? Commented Sep 28, 2019 at 3:22
• the question looks like a doodle with no specs on V,I,Z,t for the load Commented Sep 28, 2019 at 12:40

For approximately 30 seconds soft start duration, there are two approaches: analog timing or digital timing.

The analog approach is to charge a capacitor through a current source (so that the capacitor terminal voltage increases linearly), and use a comparator to detect when the capacitor reaches a threshold.

A cheaper analog approach would be to charge a capacitor from a voltage source, through a resistor, then use a comparator. That’s not as good because the voltage rise is exponential instead of linear, and that makes it harder to control the timing. (Note: the buzzer should not be powered through the resistor.)

Either way, the capacitor is the biggest source of error. Capacitance will change over temperature and even change with applied voltage. Typical variation may be on the order of 80%, which is isn’t great.

The digital approach is what @Hearth is suggesting, use a microcontroller to handle the timing. If this were 1980 I’d suggest using a 555 timer or one of the related intercil timer/counter chips, but in 2019 it’s cheaper and simpler to use a microcontroller. That will still require a timing source, but a cheap tuning fork watch crystal or even the microcontroller’s internal RC oscillator should be good enough.

When you’re selecting a microcontroller for this application, some features to look for are internal oscillator, internal LDO regulator, cost of development tools and licenses (free is often possible), and how easy is it to find a community that uses and supports that chip. ARM such as STM32 are often a good choice, as are PIC / AVR.

• An AVR (such as the ATtiny10) may not even need regulation, since it can operate from 1.8 to 5.5V (assuming that the PoR doesn't kick in). Also, I would not entirely discount using a CMOS 555 (such as the MIC1555) in this case. Tantalum capacitors tend to be reasonably stable across the specified temperature range, and a 10MΩ resistor + 3.3μF cap tied to the THRES pin would provide a ~33s delay. Commented Sep 27, 2019 at 21:31

A simple capacitor will not do what you want without some huge values that will also have other negative effects.

Realistically, for 30 seconds, even a 555 is not a great solution, as it will require some unusually large values, and as mentioned, isn't particularly cheap anymore.

The AVR or PIC microcontroller solution is the best case for a beginner to get up to speed quickly and have a workable product.

As you didn't specify timing tolerance, I'll ignore it. Specs you will need to look for when choosing your microcontroller:

• Internal oscillator
• Operating voltage in the 2.5-3.6v range (larger is okay too)
• Output current supplied by pins greater than the current required by the buzzer

That last requirement is a soft requirement - You can get away with tying two outputs together, although this is not good engineering practice if you choose to go into production.

Since the application requires it to be super light weight, not much more weight than the 3.5v coin battery itself, I used an analog approach.

The application in mind includes a fast and sudden spin force so I was able to create a small wire switch that would close some magnetic points as soon as the spin started up, turning on the buzzer. Manually turning off the buzzer was required so this solutions works perfectly.

Thanks for all the input because it helped me cross electronic timers off the list of possibilities.

• Clever solution, though the mechanical approach may lead to long-term reliability issues. Commented Sep 30, 2019 at 21:20