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  1. itsmeRICK

    Oscillator circuits

    Touch switch or finger tracking device? We used a 74HC14 connected as a schmitt trigger, driving the counter input of a Philips flash 8051 controller and monitored the frequency shift. The oscillator ran between 100 kHz and 250 kHz. The frequency depneded heavily on circuit layour and the...
  2. itsmeRICK

    Magnetic Tattle Tape Security Strips?

    ...and what would you use this information for?
  3. itsmeRICK

    Error-amp

    Your questions are of a general nature, but good answers require detailed information on your application. General answers: How does the error-amp of a switch mode power suply work? They adjust the operation (usually duty cycle or frequency, sometimes firing phase) of the output stage to...
  4. itsmeRICK

    one pulse switch...

    I think bubulindo needs a monostable. A monostable gives one pulse of a preset durration in response to a triggering pulse. You can use an 74HCT123 or even the old NE555 could to the trick. You should use something like a 2N2222 as a buffer as inbucska sugested. One place you can find some...
  5. itsmeRICK

    Weird results from air-core transformer

    I think you will do well to take a look at some applications notes on switchmode power supply transformer design since this is what you are trying to design. None of the app notes I've seen deal with air cores, but the basic principles are the same - reduce leakage fields by increasing coupling...
  6. itsmeRICK

    Weird results from air-core transformer

    The loose coupling results in high leakage inductance, so as the frequency goes up, the regulation problem will get worse. If you aren't transferring very much power, a pair of back-to-back zeners across the secondary would help stabilize the voltage. On apporach to transfering power to...
  7. itsmeRICK

    Constant current LED driver

    Dear Mr. Taylor, I can design the circuit for you and email it to you if you send me your email address. You can email me at cappels @iname.com. No charge, of course. Dick
  8. itsmeRICK

    Weird results from air-core transformer

    It looks like the transformer's primary and secodary are looslely coupled and there is some resonance in the secondary. The loosle coupling would explain why the output voltage doesn't track the input (VCC) voltage changes, and the resonance coupled with the loose coupling results in the...
  9. itsmeRICK

    LED life

    It depends on the LED, the way you are driving it, and somtimes (but one hope not) the way you mount it in your product. If this is a serious concern, press the manufacturer of your device for details and life test data for the part you are planning to use. Even though red GaAs LEDs have (in...
  10. itsmeRICK

    measuring frequency

    No shortage of solutions. Make a one-shot with a pulse width much less than the minimum period and pass the pulse through a low pass filter. For your application, a 25 us one-shot should work. Make the low pass filter corner (it can be a simple RC) somewhere around 1 kHz if that's fast enough...
  11. itsmeRICK

    what is the best freeware program for making electrical schematics?

    Any paint program. Go to http://w1.859.telia.com/~u85920178/ the find and click on Draw cctss/PCBs in the menu on the left. Good enough for small analog projects.

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