clock/timer

[j2k]

hey guys
i need to build a timer that beep evry 15 seconds. i dont think i can use a 555 timer as i need a very low consumption timer. im working with a power supply of 3V.
please help..
cheers,
jean

 

[FRIED]

https://www.electro-tech-online.com/custompdfs/2005/03/LMC555.pdf

 

[audioguru]

Hi Jean,
If you use LMC555 you will need two of them plus a gate.
A CD74HC4060 is guaranteed to work with a supply voltage down to 2V and is also very low current. It has an oscillator that can be at a reasonably high frequency thus use a small cap and has a digital divider to provide long timing periods.
**broken link removed**

Make a power-up reset circuit for its reset pin 12 with a resistor to ground and a capacitor to +3V.
Make its oscillator about 540 Hz and its buffered output at pin 9 is your beeper frequency.
Its pin 3 output will have a signal that goes high for 15 seconds and low for the next 15 seconds.
Make a transistor beeper driver and a NOT-AND gate with three PNP transistors like my attached sketch. Use pin 5, 6 or 7 for "beeper duration".
Select transistors and resistors to match the current of your transducer.

 

[Phasor]

Ummm.. audioguru.... in your circuit, after you drop a volt or so across each transistor, how many volts do you have left for your beeper? Not very many, I suspect. :roll:

 

[j2k]

audioguru,
is the circuit u gave me applicable?
i am actually doing a device tt captures a squence of light from a target then, translating that light signal to time the clock for the device to ring at the desired time.
we will be using an atmel 2313 micon. do i still need a 555 as a timer? or can i jz attached a clock to the micon and let the micon time it.
will it be accurate??
please help.
thanks.

 

[Nigel Goodwin]

audioguru,
is the circuit u gave me applicable?
i am actually doing a device tt captures a squence of light from a target then, translating that light signal to time the clock for the device to ring at the desired time.
we will be using an atmel 2313 micon. do i still need a 555 as a timer? or can i jz attached a clock to the micon and let the micon time it.
will it be accurate??
please help.
thanks.

That's the first time you've mentioned a microcontroller, so how was anyone supposed to know?.

You should easily be able to do your entire project with the Atmel, no other chips required.

 

[audioguru]

If he is going to use a crystal controlled microcontroller, why are we talking about oscillators and counters?

Why would saturated transistors have a volt or so across them unless they were conducting 20A? My Plants Watering Watcher project has two 2N3906 transistors in series and with a 35mA load, when saturated have about 0.06V across each one. The key to good saturation is a high base current. I feed the bases a whopping 3.4mA, and their current gain is about 300.

 

[Phasor]

Why would saturated transistors have a volt or so across them unless they were conducting 20A?

Oops. Yes, yes, after checking a few graphs on datasheets, I conclude that you are correct on this one. (although your 0.06V is still pretty low)

 

[audioguru]

Hi Phasor,
I chose Fairchild 2N3906 transistors beacause they saturate better than other makes. Mine are a little better than this typical: