Electronics > Beginners
Potentiometer value with ADC
ogden:
--- Quote from: admiralk on August 10, 2019, 01:54:31 am ---I was talking about >100 ppr, you are not going to get that for $.50. 24 ppr should work as I have it figured out.
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Clock will be fine with any encoder (that still works). High resolution > 100ppr encoders are for precision applications like CNC controllers. Using such for clock dial would be gigantic overkill.
admiralk:
--- Quote from: james_s on August 10, 2019, 04:58:41 am ---Why would you hope I'm not serious about the GPS module? I'm absolutely serious, you're building a clock right? A GPS module is great for a clock, it's an absurdly cheap device that spits out a ridiculously accurate timing signal and there are libraries to parse that down to whatever you need. The potential accuracy achievable will put anything short of a fullblown atomic clock to shame. GPS receivers have many uses outside of navigating, they even use them to synchronize the flashing of buoy beacons without requiring any sort of connection between the buoys.
Why do you need 100ppr? Or even 20ppr? Even an encoder with something crazy low like 5ppr would work fine for setting a clock. I'd even go so far as to say that the lowest ppr you can find is probably going to be better because if you have a really high resolution encoder you will either have to scale it in software and throw away a lot of that resolution, or you are going to have to make very small and precise movements to set the time. The beauty of an encoder is you can twirl it multiple revolutions, or a fraction of a revolution, it doesn't matter, it produces a relative output.
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OK, I did not think about GPS keeping time, but I guess it needs to. I am used to it giving crap directions down roads that do not exist or even into lakes. A RTC will be plenty good enough for this project, but I will keep the GPS deal in mind for future reference.
My thinking on the ppr bit is that each pulse will increase, or decrease, the number. If I have to spin the knob 10 X, it is not much better than using a button. I also do not want to overshoot the number, another problem with buttons. I am thinking of it in terms of what I expect to happen when I turn the knob, which I do not know until I build something. Unless I am mistaken, @ 5 ppr it would take over 2 complete turns to set hours from 0 - 12, or even one complete turn when considering +/- ability. A person cannot comfortably turn a knob one whole revolution in one action, it is probably closer to 1/2 a turn. That means 2 turns to turn the knob once. Until I have something to breadboard, it is all academic, and I have no idea how it will work in real life. It is, however, always easier to scale down than up.
james_s:
You're confusing GPS receivers with GPS navigation units. A navigation unit contains a GPS receiver but the receiver itself just spits out strings of data, this data includes raw coordinates as well as an extremely precise time signal because the way GPS works relies on very precise timing. The GPS satellites each have their own onboard atomic clock and everything has to be perfectly synchronized because your position is calculated from the time the signals from the various satellites take to travel from the satellite to the receiver module. It is the most accurate timing source available to the typical civilian.
My example of 5 ppr was a bit extreme in order to make a point. Pick up a cheap encoder from China and play with it, the sort you can get for a few dollars are the same type typically used for things like volume controls on stereo systems.
admiralk:
The ones I ordered are < $2, so cheap enough and will be here Tuesday. I got one with detents and one without. As long as they are slight, I think it might be better to give a more positive feel of being on the number without having to concentrate on the number. If they are too tight, I can just use the free wheeling one. I am hoping that for minutes it will not be too much travel because I overlooked switching from hours > minutes > seconds. The push button would be better used for that.
Thanks for clearing up the GPS bit. I knew they used time for positioning since they can be used for things like speedometers, just never thought of them as being used for actual clocks.
james_s:
GPS was designed for positioning, hence the name. In recent years though the receivers have dropped in price to the point where they cost only a few dollars each making them economical for purposes that have nothing to do with navigation. They even make receivers specifically optimized for timing, these have a 1pps output that occurs precisely at the top of the second.
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