Re: good scopes for coiling

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Paul B. Brodie" <pbbrodie@xxxxxxxxxxxxx>

Terry,
Thanks. Please, I am not trying to criticize your TCT design in any way. 
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.

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. 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. 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. What really concerns me is that on this web 
site, 
<http://home.cogeco.ca/~rpaisley4/LM555.html>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). 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!!!

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? 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. 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.

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

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.
Paul
Think Positive

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

> Original poster: Terry Fritz 
<<mailto:teslalist@xxxxxxxxxxxxxxxxxxxxxxx>teslalist@xxxxxxxxxxxxxxxxxxxxxxx>
>
> Hi,
>
> Use this data sheet (figure 12):
>
> 
<http://www.national.com/ds.cgi/LM/LMC555.pdf>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" <<mailto:tesla@xxxxxxxxxx>tesla@xxxxxxxxxx>
>>...........
>
>