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256  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Maximum pin toggle speed on: June 14, 2009, 03:58:08 pm
@condemmed

i'm a bit surprised you come with 2 cycles for
Code:
PORTD |= B1000;
and 2 cycles for
Code:
PORTD &= B11110111;
because I've benchmarked & runned real time with big N this
Code:
for(i=0;i<N;i++){
    PORTD |= B1000;
    PORTD &= B11110111;
  }  
in the arduino standard sketch and I come up with one cycle each instruction. Of course, in that case the iteration overhead consumes 6 extra-cycles whatever inside the loop hence a total of 8 cycles.

Please note my benchmarking method cannot trace execution time when using
Code:
while (true) {
    .....
  }
which was my initial question.
257  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Maximum pin toggle speed on: June 14, 2009, 01:35:43 pm
Could someone tell exactly how many cycles uses the while(true), I mean the overhead or surrounding
Code:
cli();
  while (true) {
    PORTD |= B1000;
    PORTD &= B11110111;
  }
For example, each while(true) loop will take 2 cycles to execute both PORTD writing / toggling but how many cycles the while(true) itself will take each run whatever instructions inside the loop ?
258  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Maximum pin toggle speed on: June 13, 2009, 10:04:27 pm
You can save one cycle from
Code:
cli();
  while (1) {
    PORTD |= 0x8;
    PORTD |= 0x8;
    PORTD &= ~0x8;
  }

and get the higher square wave frequency with
Code:
cli();
  while (1) {
    PORTD |= B1000;
    PORTD &= B11110111;
  }

259  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Arduino + Vacuum Tubes as a transistor on: October 21, 2009, 03:30:10 am
Well, with tesla engineering, low Ron value is necessary but it is also crucial to have very low rise on - fall of fet switching, very low rise on - fall off fet's body diode along with a capacity to accept high voltage power supply (i.e. 500V)  pulsing primary coil & very fast frequency with low duty cycle.

Once you hit 50KHz - 200Khz, PW between 5% and 50% as in my projects, i don't think arduino TTL output drivers have so much sharp edge plus cannot provide peak local current to charge fet's internal gate capacitor. From high voltage & back-emf protection point of view, I rather use digital isolator then high speed power mosfet driver to really make pure PWM and saturate my actual "classic mosfet".

As I said before, i don't know if "logic level mosfet" has internally the equivalent of high speed power mosfet driver (i.e. TC4423 or MCP1403) which would be neat to simplify PCB, remove additional power supplies and lower $ project costs.
260  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Arduino + Vacuum Tubes as a transistor on: October 21, 2009, 02:04:37 am
Thx Grumpy and AWOL about bringing me awareness of "logic level mosfet".

Please note my projects involved Solid State Tesla Coil and Rife healing plasma tube devices with direct frequency and pulse width software generated by arduino. This is why i'm using specific Tesla Coil or Ruhmkorff driver including digital-isolator and IC driver to control mosfet to protect my arduino board and Macintosh.

It might not be relevant in this thread because the initial question does not involve same high voltage and fast frequency switching as found in Tesla engineering but do you think "logic level mosfet" has an advantage compared to "classic mosfet" i'm using so far such as IRF family and power IC drivers ?
261  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Arduino + Vacuum Tubes as a transistor on: October 20, 2009, 06:08:18 am
Quote
Not entirely true; many FETs have a "logic" version, where saturation is achieved with logic level voltages.

I would be interested to have this reference or P/N of such FETs.

Please note my application uses IRF540 & IRF840 to pulse extremely sharp on-off up to 1Mhz with very low PW which requires external FET driver IC.

P.S. The main point being stressed in this thread being best to use an opto-isolator or other tech isolator between TTL arduino and any FET tech or vacuum tube otherwise boom arduino or computer via USB link smiley-wink
262  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Arduino + Vacuum Tubes as a transistor on: October 20, 2009, 05:35:44 am
Grumpy_mike gives wisdom advice.

You need to opto-isolate (i.e. 4N25 for low speed switching) or for fast switching, best use magnetoresistive-isolator (i.e. IL610)

Indeed for saturating a mosfet or a vacuum tube, you need to bang it with higher voltage & peak current totally incompatible with arduino TTL outputs drivers.
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