Any tips for making a quick and dirty adjustable-ish square wave generator?

Thread Starter

dr.evil

Joined Aug 18, 2010
80
Gents,

I'm in urgent need of said square wave generator, do anyone here have any experience? I don't care that much about precision, drift and stability since it's quick and dirty, here are my main parameters:

Output: 0-5v, and should be able to drive a transistor i.e. source sink about 10mA
Frequency: adjustable between 1-2MHz or even better 0-2MHz
Duty cycle: adjustable between 0-5%

Any suggestions please?

Evilly yours
Dr. Evil
 

k7elp60

Joined Nov 4, 2008
562
A 555 will probably go as high as 1mhz, a MC4024 will go from about 1hz to about 20 Mhz.. Then there is a ring oscillator with a TTL ic like a7405 that might work.
 

AnalogKid

Joined Aug 1, 2013
9,362
Use a NAND gate, not an AND gate. For the simple circuit to work, the device must be inverting and have Schmitt Trigger input(s).

Search for CMOS gate oscillator. These usually are based on a NAND gate or inverter. I recommend something in the AC series of CMOS parts because of the strong output current, such as the 74AC14. For the very small duty cycle, you will need an extra resistor and a fast switching diode (1N914, 1N4148). Note that while the frequency and duty cycle can be adjusted separately, they are not independent. Changing one changes the other; that's what comes with quick and dirty.

Your question is not clear, but implies that you want your entire frequency range in a single adjustable span. This will not work. The resistor and capacitor sizes necessary for 1 Hz will not function at 2 MHz.

ak
 
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