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16  Using Arduino / General Electronics / Re: Problems with a MOSFET relay on: August 09, 2013, 08:46:31 am
Yeah, I'm trying to eliminate places where there may be an exposed pad or wire connection, or even the very edge of the PCB itself since the strip will have copper exposed to facilitate soldering two together (instead of a header since there is no room for one on either side).  The solder pads extend to the very edge on the board, it's cut and sanded that way.

So yeah, I would prefer to cut VCC from them and leave the GND plane connected.  If a data or clock line comes in contact with it, nothing will happen.  If it's a VCC line, well shit.  The other way around if either the data line or clock touches the live VCC, it will burn out the LED driver(s) and possibly other components.

I'll look around for a P-channel setup.  I think I saw one last night but I was too tired to focus.
17  Using Arduino / General Electronics / Re: Problems with a MOSFET relay on: August 09, 2013, 08:24:59 am
This only cuts the ground to the string, not the whole device.  That's done that way on purpose.  So if something else that is live contacts that live VCC plane ...
18  Using Arduino / General Electronics / Re: Problems with a MOSFET relay on: August 08, 2013, 11:39:00 pm
It will put the full battery power onto the strips which have a ground plane on one side and VCC plane on the other side.  So if anything that happens to be connected to either ground or something else on the circuit (a broken wire for that matter), happens to touch the exposed LED pads, or where the strips are soldered together, that will cause either a short, or some other type of damage.  I've always been told to never leave a high side connected to anything for that reason.  So I prefer to cut the VCC line as opposed to the GND.

So how would I do that?
19  Using Arduino / General Electronics / Re: Problems with a MOSFET relay on: August 08, 2013, 10:06:12 pm
*bump*

(before I start a new thread)
20  Using Arduino / General Electronics / Re: Just got SMD gear, now wheres the DIY SMD Arduino files!?!?!? on: August 08, 2013, 08:25:56 am
Single sided SMD, probably not.  But you can roll your own from existing files.
21  Using Arduino / General Electronics / Re: Problems with a MOSFET relay on: August 07, 2013, 06:10:27 pm
Quick question, how can I reverse the attached schematic so that I'm cutting off VCC, and not GND.  I don't want the connector (which goes to an LED string) to have live VCC on it as that could potentially cause problems.
22  Using Arduino / General Electronics / Re: Reading Li+ voltage on ADC on: August 07, 2013, 05:12:37 pm
The exact reading at 4.2V will depend on exactly how close the switching regulator holds to 3.3V. An alternative way is to use the internal 1.1V regulator, and divide down by about 4.5 to 5. I say that instead of 4, because the 1.1V internal Aref is not exact, but should be very time and temperature stable.

Ok, I think I'm going to stick with the two 18Ks only because, for now, I'm going to trust that the Buck/Boost does what it claims it can do, which is to provide a solid 3.3V whether the battery's at 4.2V or 2.0V.  But also, because I've never worked with the internal Aref and at this point I've done a code freeze for this particular version.  In the future I may very well re-open this can and look inside ...
23  Using Arduino / General Electronics / Re: Reading Li+ voltage on ADC on: August 07, 2013, 01:40:30 pm
Uh, no ... 48 LEDs only.  1,000 LEDs in the configuration that I have them will translate into a stick that's almost 20 feet long.  I don't know anyone with an arm that long. smiley  Even at the current 18" length, it is a bit too long ... I need to shorten the controller part (which is the inner circle in this picture.)

24  Using Arduino / General Electronics / Re: Reading Li+ voltage on ADC on: August 07, 2013, 11:01:00 am
What does that do for resolution though, going that low with it?

And thanks for all your help so far!
25  Using Arduino / General Electronics / Re: Reading Li+ voltage on ADC on: August 07, 2013, 04:05:15 am
Ok, so with the Buck/Boost in place, with the ON/OFF switch, is this what you're talking about?  Having the two 18K to divide the voltage and feeding into ADC0.
26  Using Arduino / General Electronics / Re: Reading Li+ voltage on ADC on: August 07, 2013, 02:06:49 am
In that case, you can just let it use the 3.3V supply as the reference, however the ADC output will be only as clean and stable as the power source. You'll still need to use a voltage divider to bring the max 4.2V below 3.3V.

Does it matter how low I bring that raw voltage?  Or should I match the 3.3V that the whole unit will be running at?
27  Using Arduino / General Electronics / Re: Reading Li+ voltage on ADC on: August 06, 2013, 07:50:37 pm
However, since there is no direct connection between the battery and the AVR, it will never measure the battery's voltage with that, only what it's receiving on VCC, which happens to be 3.3V because it's coming from a Buck/Boost.  I need the raw voltage from the battery. So I have to read it from somewhere.
28  Using Arduino / General Electronics / Re: Reading Li+ voltage on ADC on: August 06, 2013, 04:59:24 pm
There is a library where you measure the Vcc against the internal 1.1V reference. So you get Vcc in Volts as the output. You do not need any analog input connected.

Care to provide a link?
29  Using Arduino / General Electronics / Re: Reading Li+ voltage on ADC on: August 06, 2013, 03:20:00 pm
If you only want a momentary indication, you'll want to take precautions to power down the AVR, not just turn off the LEDs. And ditch the Arduino and just use a bare AVR, because other parts on an Arduino use power. Use as slow a clock as will give you a readout in a time you consider reasonable, as a faster clock means more power consumed.

I can't power down the AVR, I need it to display the gradient on the LEDs.  But, basically what it's doing (or what I'm planning to do) is this:
a) turn switch to ON which provides power to the AVR - there actually is a Buck/Boost that provides the 3.3V and I completely forgot to add that in the schematic above, that's my bad:  battery -> Buck/Boost -> AVR
b) there's a straight line from the battery's VCC to the ADC
c) AVR comes on, with everything else powered down still (uSD card, LEDs and LED drivers), ADC samples in raw battery voltage (20 times over a 2 second period) and calculates the numbers needed for the gradient display.
d) turn on the LED drivers, followed by the LEDs (drivers come on at max output so I need to shut their output off before turning on the LEDs)
e) display gradient on the LEDs for 1 seconds
f) now turn uSD card on and enter main program loop

I realize there's a lot going on, and there WILL be drainage in other places going on, however I'm also not looking for a dead accurate number in the double decimal digits here.  Just a rough estimate.  I need to know if the battery is at 4.2V or reaching 2.7V ... I will probably cut it off at 3.0V anyway ... but if in one instance the battery was at 3.1V or 2.9V and it got cut off in both situations, I'm okay with it.
30  Using Arduino / General Electronics / Re: Reading Li+ voltage on ADC on: August 06, 2013, 03:10:21 pm
It is safe to do but will not give you a valid measurement. As the battery is both the Vcc and Avcc source voltage then the internal analog reference voltage will also be the battery voltage, thus a analogRead() will always return a value of 1023 counts no matter what the specific battery voltage is.

Odd, I'm getting readings other than 1023 here.  When the battery is drained to 2.7V, I'm getting 547 and with it charged to 4.19V, I get 855.  Oh wait ... this is using an Uno to test, I think AVcc is isolated ... will have to check schematic for that.  The final (production) unit has AVcc isolated with a ferrite bead, as in VCC -> ferrite bead -> AVcc.  Would that be enough?
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