Moderators: Dave Moll, Andrew Davie, Steve Anderson
Steve Anderson wrote:It possibly is component tolerances, not just the Rs or Cs, but the PLL (the 4046). These things are notoriously sensitive to the supply voltage, The HC etc versions are far better, but you can't use them above 6V. This isn't a problem in the NBTVA motor control circuit as the VCO isn't used.
Next, what frequencies are you trying to get out of this?
What is the reference frequency going into pin 14 of the 4046?
(Note, it's not pin 64!).
If it's not 1kHz you' need to fiddle around with some caps and resistors. What voltage are you running this on? It does make a substantial difference.
Given those figures I should be able to steer you in the right direction.
Steve A.
Steve Anderson wrote:Right, 400Hz reference frequency and you want 800/1200/1600 and so on up to 3600Hz, correct? This cannot generate frequencies lower unless followed by a divider.
If you're using HC devices at 5V the Rs and Cs will be possibly be very different, this is an analogue chip with some logic thrown in. If you're still using a CD/HEF device for the 4017 that also needs to run on 5V - I know that's stating the obvious.
There is also another huge difference between the CD/HEF devices and the HC versions. The HC version VCO cannot be swept over more than a 4:1 ratio. In the vast majority of applications this isn't a problem, but here it is. The HEF/CD versions can be swept over a ratio in excess of 16:1. Just because the both carry the 4046 label doesn't mean anything, they are design-wise very different devices. This is a problem when incorporating analogue devices with logic silicon. Compromises everywhere.
So the upshot is that this isn't going to do what you want, sorry.
If you can state in total, completely, what frequencies you want then perhaps I can work something out.
Steve Anderson wrote:Harry, wouldn't it be easier to start with a higher frequency and divide that down to whatever you wish?
Let's say 40kHz, from that you can get a whole bunch of various line rates, then divide that by however many lines you want per frame. Say a 4060 (and maybe a few gates) to get the line rates you wish followed by a 4040 to select lines per fame (again possibly with a few gates). If you only want powers of 2 for 32/64/128/256 lines then the gates wouldn't be required.
Makes sense to me.
If you can say what frame rates and lines per frame you wish I can knock something simple up quite quickly.
Steve A.
Steve Anderson wrote:There's nothing wrong with using a RC oscillator here, it is for NBTV which although it would be nice to crystal-lock frequencies, it's not essential. Remember the origins of this are mechanical, aside from Swiss-made watches not many mechanical things have that degree of accuracy - at least those which we mere mortals can afford.
Give me a couple of hours, I'll sketch something up.
Steve A.
Steve Anderson wrote:I don't about you guys, but I find the internals of the 4060 a bit confusing with its odd missing outputs. So to help me (and perhaps you) I drew up this sketch to end the confusion once and for all. I haven't shown the full MR path as that should be clear.
I must set the default font to a better one!
Steve A.
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