A friend has a 120 volt converter on his truck and asked me to make a warning beeper to indicate when it is turned on.

It should beep roughly 2 seconds off and then one second on.

I have a bunch of small power supplies from PC speakers, Modems, answering machines, etc. in the range from about 3 to 10 volts and 100 to 1000 Ma.


There are a number of websites showing how to computer R1, R2 and C1 to get this timing.


Here are the Piezo buzzer specs
Operating Voltage 3-24V
Rate Voltage 12 V DC
Buzzer Type Piezoelectric
Frequency 3900±500Hz

Termination Lead Wire
Drive Method Drive Circuit Built-in
Sound Pressure Level 87/30dB
Max Current Rating10mA

Please see the attached schematic in pdf format

Can I connect points AA, BB and CC on Fig 2 to the corresponding points on Fig 1 ?

Can I connect points BB and CC on Fig 3 to the corresponding points on Fig 1 ?

Are current limiting resistors needed anywhere. ?

What cautions/suggestions do I need to observe to prevent unwanted side effects. (like maybe blowing up his truck).


Thanks in advance.

 

Can I connect points AA, BB and CC on Fig 2 to the corresponding points on Fig 1 ?

Almost. BB to BB requires a 4.7K resistor.

Can I connect points BB and CC on Fig 3 to the corresponding points on Fig 1 ?

Yes, direct connect.

What cautions/suggestions do I need to observe to prevent unwanted side effects. (like maybe blowing up his truck).

Not much. An inline fuse will make you feel safer, anything between 0.1A and 1 A.

For the on time to be less than the off time, you'll need fig. 2, not 3. You can direct connect fig 3 if the 555 timing components are modified with 1 or 2 small signal diodes. The piezo will be fine either way.

ak

 

Maybe another way is ( Fig 1 & 3 ) connect AA to Buzzer BB & BB to CC; when output is low, buzzer on
If timing Rs are about 100k ea. C = 10 uF, then pin 3 high for about 2 sec., buzzer off, C charges to 8 V, 555 resets in about 1 sec., pin 3 low, buzzer on. Buzzer might be at a low level when pin 3 high as pin 3 does not completely reach Vcc, 12V.

 

Maybe another way is ( Fig 1 & 3 ) connect AA to Buzzer BB & BB to CC; when output is low, buzzer on
.

DUH!!! (feel like a dummy).

ak

 

Maybe another way is ( Fig 1 & 3 ) connect AA to Buzzer BB & BB to CC; when output is low, buzzer on


I am not sure I undestand this. Doesn't this connect Vcc to Ground ?

 

This would be easier if each lead had its own letter. Vcc thru buzzer to ground via 555, pin 3.
Connect buzzer + to Vcc, buzzer - to 555, pin 3.

 

This would be easier if each lead had its own letter. Vcc thru buzzer to ground via 555, pin 3.
Connect buzzer + to Vcc, buzzer - to 555, pin 3.

OK, I understand.

Thank you

 

Thank you all.
I connected the buzzer from pin 3 on the 555 timer to ground and it worked perfect.