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Re: good scopes for coiling

Original poster: Terry Fritz <teslalist@xxxxxxxxxxxxxxxxxxxxxxx>

Hi Paul,

At 05:12 PM 5/20/2005, you wrote: 
Terry,
Thanks. Please, I am not trying to criticize your TCT design in any way.


You better not!!!  :o)))

I'm just trying to understand it as thoroughly as I can. I apologizes for being such an itinerant perfectionist and general pain in the b..., it's my nature and I can't help it.
I have always had this thing about needing to know everything there is to know about something and then getting it exactly right. It probably causes me an inordinate amount of extra work. 

Gosh!  Don't look at my DRSSTC schematics :o)))


I studied the data sheet you pointed me to. I still don't understand why you left off the supply voltage connection to pin #4. 

"left off"???  It IS there...

http://hot-streamer.com/TeslaCoils/Misc/TCT/Image11.gif

Active low reset IS tied to the positive voltage.

A lot of sources I've read about the 555 says that this can cause anomalies and this data sheet shows this connected. I assume that you haven't had any problems or maybe it just isn't significant in this application.

Many 555's will not work and some do with pin 4 open. It depends on who makes it and which way the wind is blowing. The pin can also pick up switching spikes and false trigger. I tied it high like everyone else.

Also, on the data sheets I have been looking at, this version is not included for 50% duty cycle. They have a different configuration. Specifically, the one that came with my LM555 lacks this version but I have looked at others on the web and none of them have this version either.

The LM555 is a linear version. It does not work as well as the CMOS version for this circuit. Only the LMC555 CMOS data sheets have it. I am not sure if it would even work on the old non-CMOS version...

What really concerns me is that on this web site, http://home.cogeco.ca/~rpaisley4/LM555.html, which is a site dedicated to the LM555, there is a schematic, using the scheme used on the TCT, shown for 50% duty cycle that is labeled as, "Inaccurate 50% Duty Cycle schematic." It says that this is an inaccurate method of producing a 50% duty cycle oscillator using the LM555 timer chip (CMOS or bipolar).

They are right. The LM555 will not work very well. They should use the LMC555 and then it will work fine. If they say it does not work with the CMOS version, maybe they don't know what they are doing :o)) Without knowing what they did, I can't guess as to what their mistake was...

Now, I have noted that you have pointed me to a data sheet for an LM(C)555 and their comment refers to an LM555. I, of course, believe the manufacturer of the LMC555 should be the source of preference for data about wiring their version of this chip!!!

They might know how it is wired... But if you call them, they will know much more about their latest and greatest chips. They will probably have to go find the "old guy" that knows anything about the 555....


When you designed this, and I realize it has probably been a quite a while back, did you reference this data sheet for the 50% duty cycle recommendation and use it or was there some specific reason that you selected this scheme over the ones on the other data sheets?

I copied it off the data sheet. It is simple fast and easy. I suppose I could have chosen from a few hundred other designs, but no other is as good as this one. One resistor, one cap, and it's done...

The other schemes use pin #7 for cap discharge, like the standard astable multivibrator mode. I do note that on the example on the web site I reference here, they leave off the supply voltage connection to pin #4 as you do.

I don't leave it off. If they do. Maybe that's why theirs does not work well :-))) Mine works fine....

So I am assuming that since you didn't include it, they leave it off, and the TCT apparently works just fine that this isn't as critical as some references imply.

You should only tie pin 4 to the positive voltage in these circuits if you want the timer circuit to work. Otherwise, just leave it off....


I am going to try and contact the owners of the 555 web site and ask them why they say that in their opinion this version of a 50% duty cycle is inaccurate. They fail to offer any explanation on the web site. IMHO, this is a major shortcoming on their part, to make a statement like this with no explanation. 

There outta be a law!!

It has caused me what I feel is a lot of unnecessary confusion and extra work.

Tell them to connect pin 4 to the positive. They left it off all their schematics. Maybe they don't have any idea what they are doing ;-))

Your time was not waisted.  You probably know more about it now than anyone!


I realize that I have probably made a mountain out of the proverbial mole hill and I again apologize. I really appreciate you taking your valuable time to try and help me to understand all this. Regards. 

Ok, but I am not sure there was a mole hill to begin with ;-))

Cheers,

        Terry

Paul
Think Positive

----- Original Message -----
From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Friday, May 20, 2005 2:10 PM
Subject: Re: good scopes for coiling

> Original poster: Terry Fritz <teslalist@xxxxxxxxxxxxxxxxxxxxxxx>
>
> Hi,
>
> Use this data sheet (figure 12):
>
> http://www.national.com/ds.cgi/LM/LMC555.pdf
>
> Since the LEDs seem to have about 5mA going through them judging by their
> brightness, I assume the current is about 5mA. You may have to adjust the
> resistors a little once you actually try it for real. Or, assume that the
> input leads are a dead short and go from there to find the current. LEDs
> drop about 1.8 volts.
>
> The output of the LMC555 goes from 0 volts to the battery voltage as a 50%
> square wave. The frequency does not matter since it is so high.
>
> With the LED drop, that is like 0 - 7 volts. V^2 / R = I 7^2 / 470 =
> ~ 10mA At 50% that is 5 mA... It does not take into account the meter
> resistance or the Tesla coil resistance so slight adjustments could be
> needed. But it should basically work fine in any case.
>
> Cheers,
>
> Terry
>
>
>
>
> At 08:54 PM 5/19/2005, you wrote:
>>...........
>>
>>I have been studying the LM555 data sheet to try and get some idea of how
>>this Tesla Coil Tuner (TCT) circuit works because it is different from any
>>other 555 circuit I have ever seen. According to the schematic that came
>>with the TCT, it is different from all of the examples included with the
>>data sheet. I'm having a lot of trouble figuring out how it functions and
>>why it didn't just use the astable multivibrator configuration. One thing
>>that really has me confused is that there is no connection to the
>>discharge pin #7 and no power to pin #6. I did note in Terry's
>>documentation that it has a square wave, 50% duty cycle output. Also, mine
>>is evidently working because the LED lights when I turn it on and stays
>>lit throughout the range of the pot. If this is the output, and Terry
>>tells me it is between 0 and 9 volts, 5 mA or less, isn't this pulsed
>>DC??? Let's say it is putting out a 100kHz 9 volt signal at 50% duty
>>cycle, what should I read on the meter set for DC volts? I think I have
>>totally confused myself and my DVM decided to go on the Fritz (oops Terry,
>>sorry for using your name in vain)! I was at least hoping to use it to
>>measure the frequency the TCT is putting out. I did find my old el cheapo
>>DVM, so I can at least measure milliamps, millivolts, and volts.
>>
>>I know that this is a mighty tough task but if you can straighten me out
>>just a little bit, I will be eternally in your debt!!! I'm really sorry
>>for being so obtuse. I hate to be a burden. Thanks.
>>Paul
>>Somehow Continuing to Think Positive
>>
>>----- Original Message -----
>>From: "Tesla list" <tesla@xxxxxxxxxx>
>>...........
>
>