I have a piezo buzzer that causes noise on the bus. I'm using a 100uF 16V electrolytic capacitor and that works fine to dampen the noise, but it holds more charge than needed and when the circuit powers down it keeps the piezo going for a couple of seconds until the cap drains.

My question is, what capacitor can I use that won't store as much power, and will drain more quickly and still work? Should I be looking at lower uF values like 50uF?

 

Hello,

Have a look at the following thread:
Decoupling or Bypass Capacitors, Why?

Bertus

 

Hello,

Have a look at the following thread:
Decoupling or Bypass Capacitors, Why?

Bertus

Thank you! I will.

 

You could also try a resistor in parallel to the capacitor. Let the cap be at 100uF value.

 

You could also try a resistor in parallel to the capacitor. Let the cap be at 100uF value.

It's a 12V piezo buzzer. What value resistor would you recommend?

 

Thank you! I will.

I think my piezo is 4KHz. What would be a good capacitor value and/or how could I calculate it?

 

Hello,

Post the complete schematic of the set-up.
This way we can see what needs to be changed.

Bertus

 

Hello,

Post the complete schematic of the set-up.
This way we can see what needs to be changed.

Bertus

Thanks you! Here is a small/partial schematic I've been working on. The piezo buzzer is remote, approx 100', from the main circuit. The dashed lines are the run out to the sounder/sensor combo. Also, the optoisolator is a PS2505 bi-directional, not a PS2504 as pictured. As you can see, this is a two line system. I can't run more lines. I have this entire circuit on a breadboard and it works fine except for the 100uf electrolytic cap on the piezo side. If I remove the cap then the noise in the system causes lots of havoc.

 

Hello,

What kind of wires do you use for the piezo?
It can be there is a pickup of signals.
Can you use a coax or other shielded cable for the piezo?

Bertus

 

Hello,

What kind of wires do you use for the piezo?
It can be there is a pickup of signals.
Can you use a coax or other shielded cable for the piezo?

Bertus

No. The wires are old security system wiring. Approx 32 of them. 18 gauge stranded. About 30 years old. I can't replace them. :-( I'm only having the problem on the wiring with the piezo, so it is the piezo causing it. I would like to replace the 100uf electrolytic with a smaller cap or a ceramic if possible.

 

Hello,

What kind of signal is going to the piezo?
Is it DC or a switched/pulsed signal?

Bertus

 

Hello,

What kind of signal is going to the piezo?
Is it DC or a switched/pulsed signal?

Bertus

Bi-directional DC. The piezo is activated by reversing the polarity. The switch in the schematic is a reed relay. This way I can constantly monitor the door switch in both polarities and simply turn on the piezo buzzer by reversing the polarity.

 

I wonder if I could use a choke?

 

You didn't say some more about this -- causes lots of havoc?

Using Toroidal Coil and capacitor LC Filter for the surge and interference of uC 5V and GND.

 

You didn't say some more about this -- causes lots of havoc?

Using Toroidal Coil and capacitor LC Filter for the surge and interference of uC 5V and GND.

Very interesting. Thank you!