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46  Using Arduino / General Electronics / Re: Automatic Switching to Battery on Power Failure on: December 23, 2012, 10:23:05 am
Charging sla's aren't that bad, they are pretty robust(I toture them often with electrically abusive experiments), probably the most effecient way would be a mosfet, a regular diode would only be worth it at low currents, a germanium diode is better but still has current limitations(as well as heat)
Basically for that size battery you will want to charge it @.3-1amp constant current untill it reaches close to 13.8, then you have it constant voltage @13.8
Easiest way is to use a lm317 although @1amp you will need a heatsink
47  Using Arduino / Programming Questions / Re: calculating error, quickest way on: December 23, 2012, 02:36:56 am
How much did that board cost? Lol I already spent 70$ on this, and I'm finally just in the final proggramming phase working on the gui,
but unless someone can figure out that formula perhaps after a certain frequency I will just have it directly change the OCR1A number and display the frequency
48  Using Arduino / Programming Questions / Re: calculating error, quickest way on: December 22, 2012, 11:10:25 pm
Yeah I wish I thought of tnat before I finished the pcb, also my budget is kinda small but anyway, how could I apply dithering ? I can't find a decent source of the actual process and how to apply it to my thing
49  Using Arduino / Programming Questions / Re: calculating error, quickest way on: December 22, 2012, 06:40:12 pm
That's an interesting idea however it will not match the actual output because the error appears to change logarithmically(as in a graph of error vs frequency) tho I'm sure there is a linear equation because I believe when I graphed the difference between errors its linear, I just can't figure it out
50  Using Arduino / Project Guidance / Re: Interfacing TDS/EC Tester/Meter on: December 22, 2012, 06:34:36 pm
Even if you found which traces the output was on, how would you get that info? And the actual number is in the processor, the only info outside it is the i/o to the lcd
51  Using Arduino / Programming Questions / Re: calculating error, quickest way on: December 22, 2012, 01:43:51 pm
Well the problem is its not typed in but in/decremented with a rotary encoder, so for lower frequencies it just goes one at a time, at higher it would need to in/decre,ent by larger values, problem is that value changes, that's why I'm looking for a formula basically that mimics the curve of the error, I'm sure its simple I'm just not too well versed in math lol
52  Using Arduino / Programming Questions / Re: calculating error, quickest way on: December 22, 2012, 11:15:16 am
I know lol, but my gui doesn't know that, I would like it to automatically know
Like where normally I change by one instead I change to the next valid number
53  Using Arduino / Programming Questions / Re: How do I get the 3d byte of a word? on: December 22, 2012, 01:00:22 am
Add
Unsigned long 3dbyte =
Before that and youl be fine
54  Using Arduino / Programming Questions / Re: calculating error, quickest way on: December 22, 2012, 12:57:56 am
I'm using this to change the OCR1A value to get the desired freq
OCR1A = (8000000/freq)-1
So say I want 247khz the ocra would be 31 and the actual freq is 258064, so quite an errror, I could just jump by ocra values at a certain point where the error gets large but idk if there's an easier way
55  Using Arduino / Programming Questions / calculating error, quickest way on: December 22, 2012, 12:50:32 am
I've got a project wher the frequncy of a timer is changed from 1hz to 1mhz, using the 16 bit timer is fine for frequency below a few khz, however above that the frequency doesn't. Transistion smoothly and starts jumping a few values, one its above 300khz its jumping by tens, 400khz by hundreds, is there a way to instead of scrolling from say 400khz to 430khz manually by changing the number until the value is enough to actually cause a change, what would be an easier way to start jumping by the error so it goes from one correct value to the next, I know I can precalculate the error and use a lookup table but I imagine there has to be a simple formula to do the same since the error is the same every time and can be calculated easily
Any ideas?
56  Using Arduino / General Electronics / Re: managing current on: December 22, 2012, 12:41:02 am
It all depends on what you wanna spend, there thousands of mosfets out there, you could go all out with a mosfet driver and a large power mosfet, or just a cheap one driven off the arduino pin
57  Using Arduino / General Electronics / Re: Strange behavior on digital pins on: December 20, 2012, 06:47:44 pm
What makes you say a value less than 100k would fry the sensor? 10k I imagine would be a better number to use, and unless it really cand handle much current you could go lower than 1k
58  Using Arduino / General Electronics / Re: managing current on: December 20, 2012, 03:02:34 pm
Id maybe look around for a better fet, maybe get away without a heatsink if it matters, unless u have heatsinks laying aeound it'll be cheaper just to get a better mosfet
59  Using Arduino / General Electronics / Re: Strange behavior on digital pins on: December 20, 2012, 10:29:56 am
Probably because that input is floating, that makes it the most susceptible to noise, a pulldown or pullup resistor would fix that, easiest just use the internal pullup on the pin
60  Using Arduino / General Electronics / Re: managing current on: December 19, 2012, 11:40:19 pm
power dissapated is current squared multiplied by resistance and rds on at 4.5v is .05 so 10*10*.05 is 5w
And I get that because P=IV, V=IR so P=I(IR) or P=I^2*R
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