still at it and it seems that i'm stuck in this curse. now my circuit is like below. the problem is... the frequency its oscillating is unstable (increasing), its like from the formula f = 1 / 2pi.sqrt(LC) that the C is decreasing. and waiting it to stabilize will take ages, its now 526KHz, it was 523KHz or something minutes ago (few Hz every second). i've tried changing capacitors value, put the circuit in metal box (Faraday cage? bought the Vochelle's. the chocolate went to the wife, and the metal box went to this circuit) but still no success. why i'm so unfortunate to get this curse?
edit: this increasing freq trend is worsen when i connect my frequency counter to it. connecting to only dso, the frequency seems to jump up and down, but still incresing at slower rate.
Hi,Safri,
Am I correct in assuming the frequency was stable when you were chasing your original problem?
If so,what have you changed since then?
The only thing I can think of,is the introduction of the coupling capacitor.
Op amps like to go into spurious oscillation when they have a capacitive load,so you may have two forms of oscillation occurring at the same time.
The frequency jumping up & down tends to point to this,where you can get mixing products between the two frequencies.
I suggest you remove the frequency determining components so the oscillator should stop working,then see if you can still see anything at the output.
Have you tried the counter input of the Hantek connected directly to the output pin of the IC,or have you only assumed that it will not read correctly?
The online manual shows the input marked as capable of 18v p-p,so the voltage divider idea was not necessary to begin with,& maybe also the coupling capacitor.
If the coupling capacitor is the culprit in your present problem,& you want to keep it in circuit,try placing a 200 ohm (or around about that value) resistor in series with the cap (on the Op amp side of the cap).
This fixed a differential amplifier which was spuriously oscillating at around 38kHz in what was supposed to be a dc control circuit!
Cheers,VK6ZGO