I have a question on an older project that Bill M. and others helped me with now on a PCB (much easier)http://forum.allaboutcircuits.com/showpost.php?p=281440&postcount=27 I am now placing (5) five timers on a single board but I would like to use only on piezo buzzer for all five timers! ( I think Bill M. mentioned it could be done quite easily) but we never got it into the schematic. Can any one help with this I'm not sure if I have to use a diode or not. Thank You, Jim
( still a newbie kinda) lol

 

Simple diodes are likely all you need. Just merge the diodes on the piezo speaker, and you are there.

 

Also called a "diode OR" circuit, in logic terms.

 

Enough help?

 

Any type? and polarity correct? thanks

 

If the piezo speaker is connected to ground then the cathodes (the end with the stripe) point to the speaker. Exact type is extremely non-critical, you can even mix types and never notice the difference. Just make sure they aren't really different, like zener diodes.

 

tx bill,
the - side of piezo is connected to pin#3 on the 555 and + to + side of PCB.similar to attch.

 

I was wondering if I can use a 1 amp. IN4001 Shack # 276-1101 diode and do I hook it up with the cathode facing pin #3 on the 555?
TY jim

 

Yes, and cathode goes to the 555. So yes again.

 

I'm back now I ordered a bunch of 500K trimmers from BG and would like to put in line with Rt ( as on schematic on post #7) to make my time more variable but i'm not sure where to attach the wiper can anyone help with this??
Thanks Jim

 

can anyone help with my last post please??? not sure where to tie in the wiper on a 500K trimmer cat. # RES1425 from BG Micro. TY

 

The wiper would go to pin #6 just like the original 270k resistor did. Only one of the other pins of the trimmer is used, tied to your supply voltage. The unused pin of the trimmer is usually tied also to the wiper.

This is done to keep the resistance in the circuit in the case of the wiper failing. Not so much something to worry about with today's components, but a hold over from the old days. You can see what I mean by this link to the forums Ebook - http://www.allaboutcircuits.com/vol_6/chpt_3/7.html If you haven't looked at the Ebook, you should, it's a great knowledge base that most forums don't have.

 

If you want a variable resistor, tie the wiper back to one leg of the trimmer. Trimmer will show a lower (or higher) value as you turn clockwise. If you want the resistance to get higher (or lower) as you turn clockwise, connect wiper to the other fixed leg of the trimmer.