Re: Another capacitive transformer TC

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Antonio Carlos M. de Queiroz by way of Terry Fritz <twftesla-at-qwest-dot-net>" <acmq-at-compuland-dot-com.br>

Tesla list wrote:
 
> Original poster: "Jolyon Vater Cox by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <jolyon-at-vatercox.freeserve.co.uk>

> For the Ping circuit a 555 astable will be used
> driven from 9 volt battery.
> R1 will mainly control frequency and R2 will mainly control the "ping"
> length.
> 
> I anticipate R1=100k
> R2=1K
> C1=10nF
> that should give
> Time high =0.7*(1e5+(2*1e3))*1e-8 = 707 uS
> Time low = 0.7*1e3*1e-8 = 7 uS
> Frequency 1400.560224 Hz.
> 
> Is this OK? I understand the "ping" is produced during the "low" period. Is
> this due better current sinking than sourcing capability with a 555 or
> faster switching time on the "low" than the "high" period?

I prefer to use a small R1 and a large R2, to have an almost square
wave output. This leaves enough time for the dissipation of the
transient caused by the low-high transition. 
 
> Would variable frequency/ "ping" length be desirable?

It's interesting to see the effects. For example, if you adjust the
system to produce a low pulse that lasts for twice the duration of
the energy transfer, the pulse with start a transient, and will
stop it when the energy returns after the first notch, removing all
the energy from the system (except for what is lost). Curious to
see.
 
> Can Pin 3 be used for the direct excitation of circuits -without any
> amplification or short-circuit protection for the IC or will this have to be
> provided- any suggestions?Also, will a ground clip be necessary to act as a
> return path for the signal?

It's possible to use pin 3 directly. A somewhat better result is
obtained with a transistor emitter follower driven by the 555, with
a small (100 Ohms) emitter resistor.
The ground connection of the system must be the same ground of the
555.
 
> I have a Telequipment D67 oscilloscope
> (25 MHz dual-trace , analog not digital, with no storage capability) will
> this suffice for observing the results of the ping test?

Yes.

> how are the test leads connected between the ping tester, the circuit to be
> tested, and the oscilloscope?

Ground connection to ground of system and 555. Atennuator probe 
connected to the top of L1-C1. A regular probe is ok too.
You can use the other probe connected to the 555 output for trigger,
or use it as an antenna to see the output voltage. Connect it to a 
piece of wire suspended close to the terminal to be observed. Look
at the primary voltage at the same time, and put the antenna just
close enough to be able to see the output waveform without disturbing
the primary waveform.
 
> Finally, could the "ping" tester also double as a lamp tester (with
> antiparallel LEDs in Pin 3 output) to determine the resonant frequency
> through the brightness of the LEDs?

Yes, but it's easier to use the oscilloscope. You will see the resonance
frequency directly in the ping test. The oscillator would have to run
at the resonance frequency (or frequencies) for use with the LEDs.