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136  Using Arduino / Project Guidance / Re: rechargable batteries for uninterruptible power supply on: October 20, 2012, 04:21:15 pm
this should measure the voltage, with a voltage divider the voltage gets 0.18*Voltage.
Alternatively it could be mounted between each powersupply and the correspooding diode. Then this goes to A0 respectively A1 to know what the battery supplies and what the power adaptor supplies.
137  Using Arduino / Project Guidance / Re: rechargable batteries for uninterruptible power supply on: October 20, 2012, 02:26:02 pm
And to understand you correctly, to use this infamous boost converter, the only thing is to add it and to change the ACtoDC-12V-converter's input to Vin_ACtoDC≤5V input and the batteries Vin_batteries <Vin even if they are completely full.

Is it a difference to use the V_IN pin or to use the power-jack at the top?

Next Idea:
138  Using Arduino / Project Guidance / Re: rechargable batteries for uninterruptible power supply on: October 20, 2012, 12:58:07 pm
Hello,
I think, the boost converter isn't necessary. This could also work with the 6*1.5V=9V battery pack and a 12V wall wart (I have a universal wall wart supporting selectable 5,9,12,... V)
And yes I already also  heard that batteries can supply more power than what they are sometimes said to supply (I measured 1.6V instead of 1.5 right now, a "Aerocell 1.5V" even if it was used for some weeks)

139  Using Arduino / Project Guidance / Re: rechargable batteries for uninterruptible power supply on: October 20, 2012, 10:19:49 am
When the mains are supplying power, the voltage at J1 is greater than the battery voltage at TB1. This causes D2 to be reverse-biased and prevents current from flowing out of the battery.
This is not clear for me, that means, always the higher power supply is taken?
I think, that would result that the sum of each voltage is supplied then, that might be too much.
And what is the sense of the diodes, then?

Some diodes like this,

I am thinking of something like this now
140  Using Arduino / Project Guidance / Re: rechargable batteries for uninterruptible power supply on: October 20, 2012, 06:51:13 am
Hello.
In my circuit, no current is drawn from the AA cells unless the mains power fails. Normally all power is provided by a 5V wall wart. AA alkaline cells are advertised as having seven year shelf life, so while I would replace them after a significant power outage, otherwise I plan on just changing them maybe every 2-3 years, just to be conservative.
Ok, that is very good - especially the first sentence. I think, if I put them in dry area, this will decrease the self-drain (self-discharge).

However, I have to admit that your circuit is very complex for me.

I am thinking of something like this (red=9VDC, blue=GND)



I have heard, relatively long ago, something with diodes so that electricity can only flow in one direction...

I am really clueless  now... And I really want to do it the way you told: "no current is drawn from the AA cells unless the mains power fails"
141  Using Arduino / Project Guidance / Re: Control all 3.3V devices with 5V Arduino ? on: October 19, 2012, 05:51:40 pm
Ok, that is fine!
And thank you very much for the help. This is a very easy way to work with 3.3V modules smiley
142  Using Arduino / Project Guidance / Re: Control all 3.3V devices with 5V Arduino ? on: October 19, 2012, 05:45:27 pm
Ok, Could I also use 10K resistors? That would minimize the current drawn.
And, thank you very much for the explanation.
143  Using Arduino / Project Guidance / Re: Control all 3.3V devices with 5V Arduino ? on: October 19, 2012, 05:35:12 pm
You should always read the data sheet for these modules, some will take 5v because the chips is able to or the module has an inbuilt voltage divider.

The modules 3.3v high outputs can go direct to the arduino as the digital inputs see anything over 3v as high.

Yeah, I knew that already smiley-wink

The question is using those 3.3V modules not having an intern voltage divider and as output.
144  Using Arduino / Project Guidance / Re: rechargable batteries for uninterruptible power supply on: October 19, 2012, 05:28:23 pm
For me it is very important to charging the batteries. There are also AA /AAA rechargable ones?
Or do you think it is a problem when they get empty while power is supplies from the wall wart?
145  Using Arduino / Project Guidance / Re: Control all 3.3V devices with 5V Arduino ? on: October 19, 2012, 05:24:40 pm
Unfortunately, I have no potentiometer, but resistors:
220Ω
1KΩ
10KΩ
each 10 times, not more.
I think 40mA is max current drawn per pin

So I have an input device whose current drawn can be ignored, 2*220Ω+1*220Ω=3*220Ω=660Ω (=R1+R2).
I = 5V/660Ω = 7.5mA

Is calculation correct?
However, that means I could also use 10KΩ because current drawn gets less with increasing resistor value (?)
146  Using Arduino / Project Guidance / Re: Control all 3.3V devices with 5V Arduino ? on: October 19, 2012, 05:04:37 pm
Aaaahrg, I mixed the order of the resitors!!
This is corrected:


My question is whether it is really that simple?!
147  Using Arduino / Project Guidance / Re: rechargable batteries for uninterruptible power supply on: October 19, 2012, 05:00:45 pm
Ok, thank you, that is not very much I guess, even if I don't know much about these units.
And I really want to simplify the battery with the  uninterruptible power supply. Jack Christensen speaks about "ideas for modest loads", I would really like to hear them.
AND I really like the idea, basically, charging a rechargable battery and using it, and then use the power from the charged battery, so please stick to that if it's possible.
148  Using Arduino / Project Guidance / Control all 3.3V devices with 5V Arduino ? on: October 19, 2012, 04:45:22 pm
Hello,

there are many 3.3V modules for other microcontrollers out there (e.g. there are Arduinos with 3.3V supply voltage).

To work with them, I though of this simple construction:


with:
R2 = 2*R1

Then we have
3.3V = 5V * R2/(R1+R2)
3.3V = 5V * 2*R1/(R1+2*R1)
3.3V = 5V * 2*R1/(3*R1)
3.3V = 5V * 2/3, check OK

So I can use for example:
 R1 = 220Ω
 R2 = 220Ω+220Ω (series switch)

---
Is this  thinking correct? Or is there any mistake. Then it is very easy because you only need one type of resistor and double it by doing series .

Thank you very much. Then I know whether I can buy all the 3.3V modules smiley

~
149  Using Arduino / Project Guidance / Re: rechargable batteries for uninterruptible power supply on: October 19, 2012, 04:22:45 pm
Unfortunately, the ampermeter I have at home doesn't work at all. So, I guess, however, the current drawn is not very high. Have connected a 433MHz transmitter 3 LEDs with each 220R and reading some sensor values (photoresistor ,. ...) and that's it.
So can you call this modest load? I don't know.
 Would be very happy with an  uninterruptible power supply smiley
150  Using Arduino / Project Guidance / Re: rechargable batteries for uninterruptible power supply on: October 17, 2012, 03:16:00 pm
How can I measure current drawn?
I think it is
Code:
power source --- (A) --- Arduino
whereby (A) is the ampermeter connected in series




I don't know if I am able to do this with my old volt/ampere-meter because it has very thick cables and my 230VAC converting power source has the Arduino power source (2.1mm) output and for + pole it has to reach the center of the socket...
I will try and post results.
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