Hi.
How would one make a circuit that has a buzzer that, upon a trigger being tripped, produces a buzz lasting, say 1 second, then stops until reset? Even with the trigger continuously depressed, the buzz can't last more than 1 second.
Try a monostable
555 in astable mode. Or use a microcontroller and generate a pleasing tone as well as timing it.
Best regards, Spehro Pefhany
-- "it's the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
How about:
Consider CD4060. Look up its datasheet to see how to make an RC oscillator out of the first section.
Imagine that you make it produce 1024Hz. You want 1024 cycles and then it stops. If you make it make 512Hz, you want 512 cycles.
Run a diode from the desired Q output to the input of the oscillator so that when that output goes high is jams the oscillator high and stops it.
The trigger can be turned into a narrow pulse with a simple RC. The trigger resets the 4060. The 4060 then counts up to the desired count and stops.
This has the advantage over LM555 circuits in that it can be very low power.
Another way, using relays:
Rly1-1 +-----|o----+ +----+----[Rly1]-----+ | | | | | | |> | | | | __ | | +---o o------------+ | | Reset | | |> | | | | | | | +------+ +--[Buz]--+ | | | | +-----| |
-- Does the buzzer have an internal oscillator? JF
It's a piezo buzzer powered with DC current. (If it uses DC, wouldn't that mean it has the internal oscillator?)
--- Yes, in which case you can use this circuit: (View in Courier)
Vcc>-+---------+-----+-------+--------+----+ |R1 |R2 |R3 8| |R4 | [10k] [10k][910k] +---+---+ [100k] | | C1 | Rt| 2|_ Vcc _|4 | |C3 +-[100nF]-+-----|--O|T R|O---+ [100nF] | | 6| | |C4 | | +---|TH 555| [100nF] | | | 7|_ |3 | | | O +--O|D OUT|O---|----|---+ | O S1 +| | GND | | | | | [1µF] +---+---+ | |[PIEZO] | Ct|C2 1| | | | GND>-+---------------+-------+--------+----+---+
C3 should be connected directly across pins 1 and 8 of the package and as close as possible to the package.
A 555 is a non-retriggerable monostable, so when S1 is made the output will go high for:
T = 1.1 RtCt
regardless of what is done with S1 during that time.
If your piezo doesn't need much current you can drive it with a 7555 and delete C3. Check the piezo specs and the 7555 specs to see if it'll work.
JF
-- A caveat... If S1 is made and held down for longer than it takes the 555 to time out and if there's any switch break bounce in S1, the 555 will be triggered again and generate another 1 second pulse when S1 is released. If that's the case, the switch will need to be debounced. Will you need a circuit for that? JF
Just increase R1 to 270K ?
-- Good one! :-) That'll work well if the bounce lasts for
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