The homepage of a relatively simple microcontroller-based frequency counter. This design is common to just about all of the kits that you'll find on eBay or Amazon (you know the ones - they don't have any instructions). Usually you'll be looking up construction variant 2 (five digit display) with a 20MHz crystal.
Designed by Wolfgang "Wolf" Büscher, DL4YHF.
Microcontroller used: PIC 16F628
If you're at a security conference, and you've got a ham radio license (of any class), grab your radio and set it to 146.580 simplex (no offset).
A website that takes a parrticular frequency (in KHz) and a duty cycle (at least 50%, or on half the time, off half the time) and calculates the values of the two resistors and the capacitor required to generate that frequency using a 555 IC.
A simple webapp that calculates the resistor and capacitor values to make a 555 generate a signal of a particular frequency.
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