I'd like to generate a 50% duty cycle, any particular tolerance or accuracy. It's just for debug propuses so, if it's not a perfect 50% duty or frequency is not stable, it's not a problem.
That's why I'm looking for a simple solution. I've seen NE555 from ST have a good documentation.
To be able to generate a 500kHz as example, I should look at 4.5 50% duty cycle oscillator, where is written:
t1 = 0.693*RA*C
f=1/(t1*2)
I calculate t1 = 0.693*180ohm*0.01uF = 1.25uS than a freq. of 400kHz?
Seems strange to me since small resistors. Can you kindly check if my logic is correct?
Try reducing C by a factor of 10.
That circuit will not give a stable duty cycle, if a variable resistor is used, because the duty cycle is dependant on the ratio of two resistors.
One simple option to get an accurate 50% duty cycle is to put a D-type flip flop (such as the 74HC74) after the oscillator to divide the output frequency by 2, which would give you a 50% duty cycle with no effort. As said above, you can find 555's that can work up to 2MHz, so getting 500kHz would be no problem, or build an oscillator around a Schmitt trigger inverter.
The tricky part will be the wide frequency range you're targetting. Doing that with just one simple RC oscillator will be challenging. If you want your oscillator to be able to switch seemlessly between the two ranges it may not be that simple. Now if you can accept glitches during the switching, that's just a matter of using a switch and switching between two capacitors for instance.
If you're going to do that, you might as well use one half of the 74HC74 as an astable. Here's a circuit I whipped up in another thread. Change the resistor and capacitor values to alter the frequency.
https://www.eevblog.com/forum/beginners/portable-low-frequency-square-wave-generator-circuit/msg2155480/#msg2155480
I don't really need a 50% duty cycle, as I said it's just for test purposes, so will never feed something that require particular clock parameters.
About 555, so, if I place small Res like 150 and 1.5k, with a 0.001uF , this will be a good choice of resistors and capacitor for this IC? I'll able to generate about 400kHz.
Than I'll regulate my frequency with a POT in series to 1.5k. Theoretically, since R1 is very small (150 R), I'll able to get between 50.5% and 53% duty cycle.
I'm right with this assumptions?
I'd liked your version with D-FF, I've tried to simulate it but I've got some problems.
https://www.falstad.com/circuit/circuitjs.html?cct=$+1+0.000005+14.235633750745258+74+5+43%0Ac+80+112+128+112+0+3.3000000000000004e-8+-2.508638357675748%0Ac+80+176+128+176+0+0.000001+-2.5001005324319188%0Ac+80+368+128+368+0+0.0000010000000000000002+-2.4956407383303683%0A155+240+208+304+208+6+5%0A155+400+176+464+176+6+5%0Aw+496+240+512+240+0%0Aw+512+240+512+256+0%0Aw+400+240+384+240+0%0Aw+384+240+384+256+0%0Ag+512+256+512+272+0%0Ag+384+256+384+272+0%0Aw+400+176+384+176+0%0Aw+496+208+512+208+0%0Aw+512+208+512+144+0%0Aw+512+144+384+144+0%0Aw+384+144+384+176+0%0Aw+496+176+528+176+0%0AO+528+176+544+176+0%0Aw+400+208+336+208+0%0Aw+240+240+208+240+0%0Aw+240+208+208+208+0%0Aw+208+208+208+240+0%0Aw+208+240+208+256+0%0Ag+208+256+208+272+0%0Ar+176+112+256+112+0+22000%0Ar+352+368+416+368+0+470%0As+128+336+128+272+0+0+false%0A174+272+368+320+368+0+1000+0.1733+Resistance%0Ag+64+400+64+416+0%0Aw+80+112+80+176+0%0Aw+80+176+80+368+0%0Aw+80+368+64+368+0%0Aw+64+368+64+384+0%0Aw+64+384+64+400+0%0Aw+128+368+128+336+0%0Aw+128+208+128+176+0%0Aw+128+112+160+112+0%0Aw+160+112+160+320+0%0Aw+160+320+336+320+0%0Aw+336+272+336+320+0%0Aw+160+112+176+112+0%0Aw+256+112+336+112+0%0Aw+336+112+336+208+0%0Aw+224+368+192+368+0%0Aw+240+272+240+304+0%0Aw+240+304+240+368+0%0Aw+272+368+240+368+0%0Aw+240+368+224+368+0%0Aw+192+368+128+368+0%0Aw+352+368+336+368+0%0Aw+336+240+352+240+0%0Aw+352+240+352+320+0%0Aw+352+320+432+320+0%0Aw+432+320+432+368+0%0Aw+416+368+432+368+0%0Ar+128+208+128+272+0+100%0Ao+17+1+0+4106+5+0.1+0+1%0A
Seems not able to regolate it with POT, also sometimes it freeze. Something wrong?
what is regolable? i never heard that term
Adj. is the correct word. Sometimes due my language some words seems also correct in english.
I'd like to use something simple and cheap. I know there's micro and advanced regulators but it's something I don't want to use.