SS's WIP GCP!

ShockSlayer · Post by **ShockSlayer** » Wed Jan 07, 2009 8:33 pm

Ok then, I need to find a way in monitor my batteries voltage. It lasts for about two hours, but it drops to 9.9v, which shuts off the gc, and the screen, ironically.

Can anyone reccomend me a good digital meter, for an 11.1v battery?

SS

Mario · Post by **Mario** » Wed Jan 07, 2009 9:24 pm

You want a low battery meter?

Try something with zener diodes, these let current pass through only at a certain voltage. You could rig something up with a 10v zener and a NOT gate, wait a minute and I'll get a diagram up.

Kyo · Post by **Kyo** » Thu Jan 08, 2009 2:45 am

that's a really good idea, mario.

ShockSlayer · Post by **ShockSlayer** » Thu Jan 08, 2009 6:06 pm

How about 10.2v, just to be safe!

SS

Mario · Post by **Mario** » Thu Jan 08, 2009 6:36 pm

Whoops, I forgot about this. Forgot to add a diagram.

I'll do that right now, after a bit of research about zener diodes.

Mario · Post by **Mario** » Thu Jan 08, 2009 6:59 pm

Okay, from what I can understand, zener diodes are just like normal diodes except that they allow current to flow in the OPPOSITE direction with a high enough voltage. Like, if you have a 5v zener diode, current could not pass backwards through it unless it is 5v or more. So here is how you would make a low battery indicator:

If you have a question, please ask.

ShockSlayer · Post by **ShockSlayer** » Fri Jan 09, 2009 1:08 pm

Ok, I have a question Can I use two 5.1v zener diodes in series? That's what I bought at the store. And what is that thing in the middle, I don't really understand diagrams yet.

And, from a little bit I read, wouldn't the LED always be on, and then would turn off when battery is low? I think it would be better if the LED would turn on when the battery was low, instead of turning off when it is low. Less waste of power?

SS

ShockSlayer · Post by **ShockSlayer** » Fri Jan 09, 2009 2:26 pm

Okay, answering self, apparently I can, because I tried it.

It dropped it(the voltage) from ~12v to ~10v. Not sure exactly, I was using an analog meter.

From my understanding:

That made the LED turn on. even when I connected it to an 18v battery, and a 7.5v wall adapter...

SS

bacteria · Post by **bacteria** » Fri Jan 09, 2009 3:52 pm

So, if we use two 3.6v zener diodes in series, are we saying that we can have an LED come on if the voltage gets under 7.2v, using SS's diagram? If that is the case, it would be very interesting...

Are these suitable? link

two of those = 7.2v which is relevant as 7.4v Li-ions seem to work at just over 8v for quite a while, slowly drops to about 6.89v when the screen goes off. 7.2v would be a good indication of a few minutes left.

Also, I know if you want to hook up a 5v LED to voltage up to 12v you add a 47R ohm resistor (so the LED doesn't blow); I presume it is the same case here?

Perhaps someone can elaborate on both points please?

Kyo · Post by **Kyo** » Fri Jan 09, 2009 3:56 pm

Those are fine, bacteria (though kind of expensive!)

Anyway, it once again depends on the draw of the diodes.

Mario · Post by **Mario** » Fri Jan 09, 2009 4:13 pm

ShockSlayer wrote:Okay, answering self, apparently I can, because I tried it. It dropped it(the voltage) from ~12v to ~10v. Not sure exactly, I was using an analog meter.

From my understanding:

That made the LED turn on. even when I connected it to an 18v battery, and a 7.5v wall adapter...

SS

I see I underestimated your smartness.

I'm going to make a real soldered-together version, the take a picture of it and show you. The thing in the middle is a transistor, 2N3904 or equivalent. What this circuit does is see if the battery voltage is more than 10.2v - if not, then it lights the LED. I'll explain more later, at school right now and obviously can't solder something for you.

And yes, two 5.1v diodes should work.

Kyo · Post by **Kyo** » Fri Jan 09, 2009 4:25 pm

Mario, SS, I believe both of you have the diodes facing the wrong way. Obviously they have to face to the + Pole in order not to just act as a regular diode

Mario · Post by **Mario** » Fri Jan 09, 2009 4:39 pm

Yeah, I realized that right after I posted it. I'll fix it when I solder the real thing.

ShockSlayer · Post by **ShockSlayer** » Fri Jan 09, 2009 4:40 pm

That was a component? Oh!

Like I said: I somewhat lack the ability to read general electronic circuits when they are like that.

Ok, lemme go see if I can find one.

Kyo, what do you mean "face?"

SS

vskid · Post by **vskid** » Fri Jan 09, 2009 5:07 pm

ShockSlayer wrote:Kyo, what do you mean "face?"

SS

Diodes are directional, like LEDs (Light Emitting Diodes). So if you have it backwards, it won't work the way you want.