Circuit Design - Button activated timer with small "chirper"?

Hello all. I have a personal need for a small circuit. I have a good understanding of components, how they are connected, and actually building them, but an electrical engineer I am not. I was wondering if someone could lend me a hand. It's probably very simple in design. Attached are my requirements:

  • Needs to be as small and light as possible.
  • Attachable with Velcro. I'm imagining a PCB where the back has a stick on Velcro pad.
  • Small momentary button that when pressed, activates a 15 second timer (approximately and no display needed). When the 15 seconds expires, a small speaker should emit an audible chirping sound (audible from within approximately 50-100 feet outdoors in a relatively quiet setting) at 5 second intervals. This chirping will continue until the button is pressed again.
  • There may be two buttons if size/weight/complexity is smaller/lighter/simpler than required circuitry with single button.
  • Replaceable battery (I'm imagining a watch size battery).
  • Should be able to take a bit of bumping around. It is for a child's use and will be attached to something that will undoubtedly be thrown or dropped.
  • Did I mention as light as possible??? :-)

I've bought from Allied et all in the past, so buying the speaker, buttons, battery holder, etc. shouldn't be a problem. The physical layout and PCB building should be something I can do. This is just a little project for my son and me so I can just etch a board (hopefully one layer is enough). I just have no idea what components to use.

Thanks very much for any assistance!


Reply to
Loading thread data ...

..Just translating the logic.

1) If state change on button then start 15 sec delay and process next. 2) Start chirp procedure (An FM modulated square wave further modulated by 5 sec blanks) 3) Exit procedure until state change on button 4) Wait for another state change to start (1)

Now the above might need some editing but it's a start and other posters may make use of this for design ideas..

To me this is a microcontroller project

D from BC

Reply to
D from BC

You should look into the beeping softballs and stuff the they use for blind pepole to play sports.

Good Luck! Rich

Reply to
Rich Grise

Ooopss...Correction to step 3

3) Exit procedure if state change on button..

D from BC

Reply to
D from BC

Unless I'm very confused, sound level from a watch-sized battery powered audio transducer is going to be very faint at 100' outdoors, even if it's quiet. I think you're going to have to look at something a bit more powerful. As another poster said, seems a natural for a uP project, except for the audio part.

Dave M
MasonDG44 at comcast dot net  (Just substitute the appropriate characters in the 
 Click to see the full signature
Reply to

The light weight requirement and 50-100' range is gonna kill your battery life. I think the first thing you need to do is find a sounder thatmeets your requirement for audibility at the range you want, and then design from there. The louder it needs to be, the more power it will take from the battery. I think a Sonalert may give you the best audibility vs power.

I'll ignore battery life for the following conceptual level circuit. (You can Google for 555 circuits) It requires 2 555's and a 4017, 2 mosfets and an SCR, plus support components:

----- / | 555 | Gnd ---o o---2| 15 |---A Switch | secs| -----

The 555 is configuired as a monostable. Each press of the switch creates a + pulse at point A for 15 seconds.

+----------+ | d|_ | | | P channel Mosfet | || +-->|-------+-----+___| |-|s D1 | | | | | | | [1K] [Sounder] | | | Gnd ----+-----+-------------+

The 15 second pulse at point a is connected to the gate of an SCR, which turns the SCR on, as long as Q1 conducts. Q1 conducts while B is negative (more on this later). That allows the 5 second 555 astable to run.

So, up to this point: 1 press of the button triggers the 15 second time to run for 1 cycle, then stop. That timer turns on an SCR, which will stay on as long as current is drawn through it. Current is drawn by the 5 second timer through Q1, so the SCR stays on and the 5 second stable will keep running until Q1 is turned off.

The output of the 555 astable feeds the sounder through Q2. Q2 is held off during the 15 seconds that point A is plus. Therefore, the circuit will not start sounding during the 15 second cycle. After that, it will sound every 5 seconds.

Now, all we need to do is control point B to be negative until the second press of the switch. You can use a flip flop or a counter to do that. I'll discuss using a 4017 counter: ----- A----|14 | | 2|---B | | | 4|--+ | | | | 15|--+ ----- 4017

The clock signal comes in on pin 14, which is connected to the output (point A) on the 15 second timer. Each press of the switch triggers the 15 second timer. Each clock pulse advances the

4017 count by 1, until the 4017 is reset, at which time the count returns to 0. As configured, count 2 (pin 4) is connected to the reset pin on the counter (pin 15). Therefore the counter can only count 0,1,0,1,0,1 etc. That means that each press of the switch changes the polarity on pin 2 (point B) from + to - or - to +


Reply to

That was an awesome reply. Electronics has always intrigued me (that's why I'm trying to expose my son to it). I've just never had the ability to "get it" at the level making even simple circuits like this one. I'm sure it took you longer to describe it and it did for your to craft it.

Everyone's point about the volume and battery life was already in the back of my mind. But I'll start by shooting for the stars and I'm sure be more than happy with a middle ground. I'm sure that 50', if attainable, would be sufficient.

Thanks very much. I'll reply back if I have any follow-up questions. But your response was excellent. I greatly appreciate you taking the time to write it.

J>> Hello all. I have a personal need for a small circuit. I have a good

Reply to

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.