time beeper

[binkabir]

hello all
very unfortunate for  i spent almost i week trying to design the circuit i downloaded from this site call time beeper and it didn't work. can any
help me out  : cos am down

 

[audioguru2]

When you are on the Time Keeper site, right-click your mouse on its address in your browser and left-click Copy. Then during your reply here just right-click your mouse on the page then left-click Paste.
That's how to post a link that works. ;D

 

[MP1]

binkibir,
This area of the forum is for questions about projects which are in the projects section of this site. Where is the time beeper?
I can move this thread to the appropriate area, but you will need to post a link so that members can help you.

MP

 

[prateeksikka]

google search did not help me too!
anyway what was ur project and which problem were u facing?

 

[MP1]

is it the one from our site?

"Timed Beeper"

http://www.electronics-lab.com/projects/oscillators_timers/008/


MP

 

[audioguru2]

Our Timed Beeper project uses ordinary Cmos ICs that are guaranteed to work only when their supply voltage is 3V or more. But the project uses a 3V battery that drops to 2V over its life.
I would use 74HCxx ICs that are guaranteed to work when their supply voltage is 2V or more, or you could use a 4.5V or 6V battery with the ICs in the project.

With a 6V battery and 74HCxx ICs, the beeper would be extra loud. ;D

 

[prateeksikka]

hi audioguru!
i guess it could even burn out at 6V.why do u call it extra loud?
are u sure?

 

[audioguru2]

Hi Prateek,
The piezo oscillating beepers I have produce a low sound level with a 3V supply, much louder with 6V and are very loud with 9V. I didn't want to deafen myself so I didn't try even higher supply voltages.

Digikey have Panasonic oscillating beepers similar to mine. They are rated for supply voltages from 3V to 20V. You can look at their datasheets to see how loud they are at high supply voltages. Since their max supply voltage is 20V, they would probably "burn out" (I think the piezo element would fracture) with 24V.

Hee, hee. ;D  Yes, I'm sure. ;D

 

[prateeksikka]

I guess a piezobuzzer has a diaphragm and it oscillated at a fast pace when supply is connected across it.
i guess the frequency of oscillations would be too high at say 30V thats why it burns out.Generally most electronic devices are rated at max 12 -15 V.I use this mark as the distinction with electrical engineering which deals with high voltages above say 20V.
HEE HEE ;D

 

[MP1]

Our Timed Beeper project uses ordinary Cmos ICs that are guaranteed to work only when their supply voltage is 3V or more. But the project uses a 3V battery that drops to 2V over its life.
I would use 74HCxx ICs that are guaranteed to work when their supply voltage is 2V or more, or you could use a 4.5V or 6V battery with the ICs in the project.

I have seen other similar comments on this forum in the past regarding CMOS voltage. These CMOS devices work fine in the 3 volt range and a little under. I think much of this misconception has come from working with TTL devices and perhaps older battery technology. Also note these devices only use micro amps of current and will last a very long time before battery replacement is needed. This circuit will draw almost nothing from the battery until it is powering the buzzer. It is like having a device that is in sleep mode until needed. Shelf life of the battery will come into play before concern for drain in most cases.
Also note that the spec sheet shows that tripling the battery voltage will quadruple the current usage of the device. Adding more voltage accomplishes nothing.

Use of this device is no different than the 3 volt system used on every electronic device such as palm pilots, data loggers, calculators, etc. that use a 3 volt backup battery to store your preferences into a ram chip. As a worse case scenario, I usually get better than 3 or 4 years from the 3 volt coin cell which is backing up data on my datalogger. How long has it been since anyone has had to replace the backup battery for their palm pilot or calculator?

These 3 volt CMOS projects are safe and reliable. They are also very compatible with interfacing to new computer and micro technology which also uses 3 volts as a standard.


MP

 

[audioguru2]

Thanks Mp, you are correct.
This project would be reliable for a long time if it used an expensive 3.2V Lithium battery like Palm Pilots have.
Look at Energizer's expensive AA lithium cells. Their 1.6V stays high over most of their life unlike "ordinary" AA battery cells. This project could even use smaller 1.6V AAA lithium cells which cost about the same. ;D

View attachment 37990

 

[Alun]

In fact it'd be even better than your graphs illustrate because the voltage drop due to the interanl impedance would be next to nothing at these very low curents.

 

[audioguru2]

Hi Alun,
The internal resistance of the battery cells is also next to nothing.
For a fresh alkaline AA cell it is only 146 milli-ohms, so at 167mA on the graph it has a voltage drop of only 24mV. The lithium cell has such a low internal resistance that it isn't even mentioned.

I've measured close to 1.6V on brand new alkaline cells but it seems to be a capacitance or surface charge because it quickly drops to 1.4V and less.