"BOUNCY" momentary startcircuit

[TomWaits]

I wanted the option of starting my amps with momentary type switches. With such a circuit I can now use smaller switches and it just increases the options.

I found a schematic on the net and then I tweaked it to my liking and I have made some boards for it. I plan to use these in my up-coming Quasi amps.

The circuit has a 7812 to lower and regulate the voltage for the 555 timer. The 555 is being used as a flip flop.

It all works well, very well but the switch bounces occasionally and I was wondering what my options are to debounce it. I would very much like to hear your suggestions.

Cheers,

Shawn.

[TomWaits]

pic

[TomWaits]

I really like these switches and they are stainless. There is also a concave version that has a slight bubble to it. Very cheap and in large supply at the surplus store.

[The Saint]

Hi

Looks like the time period for the trigger part of the cct is to
short.
I would try increasing the value of the 220nf cap and or the 10k resistors that set the threshold voltage on pin 2.
Perhaps even increase the cap in pin 5 to 100nf.
The 10k resistors on pin 2 will determine how fast the 220nf cap gets recharged.
When the switch is depressed and bounces the cap is already recharged. So i would say by increasing the charge time, hopefully
the bouncing of the switch will happen before the cap reaches threshold voltage and is ready to be triggered again.
Sounds good in theory anyway....

[richie00boy]

Originally posted by TomWaits
I really like these switches and they are stainless. There is also a concave version that has a slight bubble to it. Very cheap and in large supply at the surplus store.

What surplus store and how cheap? I find those at RS here and they are anything but cheap!

[anatech]

Hi Shawn,
You should try a larger electrolytic capacitor after the regulator as well. The normal 555 uses a totem pole output stages and puts big current spikes on the supplies. There is also a CMOS version that does not suffer from this (7555 I think).

-Chris

[TomWaits]

Originally posted by The Saint
...I would try increasing the value of the 220nf cap and or the 10k resistors that set the threshold voltage on pin 2.
Perhaps even increase the cap in pin 5 to 100nf.
The 10k resistors on pin 2 will determine how fast the 220nf cap gets recharged...

I will pick up some more caps to experiment with and try these suggestions. Thanks!

Originally posted by richie00boy
What surplus store and how cheap? I find those at RS here and they are anything but cheap!

No they don't look cheap and they have screw type lugs on them! I think they are a buck or two each at Active Surplus downtown on Queen Street. They have two cases of these. One flush as shown and another with a bevel on it.

Originally posted by anatech
Hi Shawn,
You should try a larger electrolytic capacitor after the regulator as well...(7555 I think)

I never would have looked to the filter cap but if I can fit something bigger in there, why not? 7555? Who knew? Thanks!

Shawn.

[anatech]

Hi Shawn,
Leave the other cap in there for HF bypass. Mount it underneath then. I would think that adding 10 ~ 100 uF should do it. Just tack it in to test.

-Chris

[TomWaits]

Originally posted by anatech
Hi Shawn,
Leave the other cap in there for HF bypass. Mount it underneath then. I would think that adding 10 ~ 100 uF should do it. Just tack it in to test.-Chris

[TomWaits]

Thanks folks, the thing works but I'm afraid the nature of the circuit is "bouncy". I tried everything on it and the circuit does work better with a 470K in place of the 220K and I will probably use the boards until I have something cooked up better. I don't think I can add a Schmitt trigger by means of adding a 74C14 or a 4093? But I'm not certain. Perhaps I can and just don't know how?

So I'm on the look out for a new momentary start circuit without bounce or somebody can get this other one to calm down a little. Back you, The Forum, all this Roy Rogers talk is getting me down.

Cheers,

Trigger Happy