Moderators: Dave Moll, Andrew Davie, Steve Anderson
Steve Anderson wrote:OK...lift up one end of R12 (22k), set POT1 to mid-way, set POT2 such that the wiper is at the end connected to pin 7 of IC2B, All being well you should have a nice sine-wave on pin 1 of the TL082 (IC2A) across the frequency range. Make sure the scope input is in DC-coupled mode (x10 on the probe as well) and the trace should move up and down the screen as you move POT1 from one end to the other. Set it so the waveform is equal pos and neg.
If all OK so far re-fit R12, don't touch POT1 again. Don't touch the scope at all, move probe to pin 7, disconnect any wires connected to this output...only the PCB, POT2 and the probe. Power-up and slowly rotate POT2. At first you'll see almost nothing, slowly a sine-wave should appear. If you can set it to 5V peak-to-peak...and leave it there. Check how it is over the frequency range.
If all OK add a 47 Ohm resistor on the board between pin 7 of the TL082 and pin1 of the connector labelled 'DDS', i.e. cut the track. Let's see if that helps...
I'm assuming you've already fitted the 100nF disc-ceramic caps I mentioned earlier, preferably right on the IC socket pins on the underside.
Steve A.
Not impressed by that recorder...forget it. Dismissive, yep, and I'm not going to explain why...except even more crap! Why not use the sound-card already in the PC - it's light-years better...
Steve Anderson wrote:Ah! I wasn't aware (or missed) the fact you'd extended the pots to off-board - that will not help either, that's adds stray capacitance just where it's not needed! Put the board back to original, though keep the 100n caps, the 47 ohm resistor and the TL082. Test it works as advertised.
'll add suggestions to make itI a bit more versatile later....
That audio 'thing' (recorder) is like a 20 year old mini compared to a brand new Jaguar...
Steve A.
Steve Anderson wrote:OK...lift up one end of R12 (22k), set POT1 to mid-way, set POT2 such that the wiper is at the end connected to pin 7 of IC2B, All being well you should have a nice sine-wave on pin 1 of the TL082 (IC2A) across the frequency range. Make sure the scope input is in DC-coupled mode (x10 on the probe as well) and the trace should move up and down the screen as you move POT1 from one end to the other.
[/quote]Set it so the waveform is equal pos and neg.
Harry Dalek wrote:....not much to the circuit here perhaps the 2 100k resistor R21 R3 wrong values ?
Steve Anderson wrote:Nope, they're fine at 100k, they could both be 10k, it wouldn't matter, as long as roughly equal. I'm not sure what's going on here, there's something we're missing...though it could be hidden in the code...
[/quote]Thinking on this a bit more...if the upper frequency is 65,000Hz or so, and the sine-wave is constructed from a look-up table of 256 values (a reasonable figure as it's an 8-bit D-A), that requires an update rate of over 16MHz, the crystal frequency is about the same (16MHz), I think the thing is running out of steam - all VERY rough figures...
It's probably good enough for rough checks up to around 10kHz, after that, you're on your own...
Steve A.
Steve Anderson wrote:I simply think they're pushing things too far. Sure, 65-odd kHz no problem, but a sine-wave? Little chance, not absolute zero, but unlikely with what they're using here..
I'll work on my version that I started a while back over the next few days, it IS a sine-wave, up to 12.5MHz and down to a fraction of a Hertz. It doesn't have the fancy display, but do you need that when you have an oscilloscope? No, not really...nice, but not essential...though there's no reason you couldn't add what is essentially a frequency counter to it...which could be useful in its own right...
Steve A.
Jeez, more rain. it's been a wet year so far, I'm getting fed up with it! The joys of living in the tropics!!
Steve Anderson wrote:The oscillator I was thinking of is in the Off-Topic section, "A Useful General Purpose Oscillator.". It perhaps could do with some simplification...skip ahead to the last few posts...
That LTC1799 version is also ideal, except only square-wave output and 1kHz minimum frequency. add 2x74H390-type dividers to get down to 0.1Hz, but still only square-wave. For sine add an EEPROM, counter and a few other bits...actually there is another way to generate sine-waves..but it may require a filter on the output...a bit of a pain...it depends on how 'clean' you wish your sine-waves to be...
Steve A.
Harry Dalek wrote:Steve Anderson wrote:The oscillator I was thinking of is in the Off-Topic section, "A Useful General Purpose Oscillator.". It perhaps could do with some simplification...skip ahead to the last few posts...Steve A.
Steve Anderson wrote:Harry Dalek wrote:Steve Anderson wrote:The oscillator I was thinking of is in the Off-Topic section, "A Useful General Purpose Oscillator.". It perhaps could do with some simplification...skip ahead to the last few posts...Steve A.
Yep, if you only need sine-waves It could be simplified significantly. After all, square waves are generally easy to generate. It's also all the peripheral stuff that makes it somewhat complex for what it is...as well as the PC interface...
Steve A.
There are also many on-line tone generators which generally will suffice for all we need here unless you need absolute frequency, levels and the lowest distortion...I can't see why for NBTV...sine. square, triangle, sawtooth....though generally only at audio frequencies your 'sound-card' can handle...
an example...https://onlinetonegenerator.com/
...also has 'maybe' useful other stuff too...
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