Interesting Spektrum DX3r Experiment - Page 2 - RC-Monster Forums

suicideneil · 09.28.2009, 03:27 PM

I modded my tx with a nice big red LED & alloy bezzal to let me know its turned on- cant miss something like that when you put the radio down on the work bench.

MetalMan · 09.28.2009, 03:34 PM

The LED wouldn't be a bad idea! Except that to incorporate it in my radio would require an additional 2 wires running through the grip area. A good idea, nonetheless.

BrianG · 09.28.2009, 03:49 PM

Personally, I would wire the LED to a comparator IC with a set threshold so it comes on at a certain voltage - a rudimentary LVA. Easy to do.

MetalMan · 09.28.2009, 03:55 PM

For my case there is already an audible LVA that kicks in at a preset voltage, the LED would just be there to remind me the battery is still being drained.

Of course it would be neat to have a 2 LED setup - green LED to remind you the battery is being drained, and a red LED to indicate low voltage.

BrianG · 09.28.2009, 04:15 PM

The radio's alarm works fine if feeding the battery voltage directly to the radio, but if you are using a BEC, regulator, etc, the displayed voltage is not what the battery voltage is. A simple LED indicating a low pack voltage would be handy. And, along with a red LED for LVA, add a green LED for "power on" so you don't forget to shut if off.

Arct1k · 09.28.2009, 04:17 PM

these work?

http://hobbyking.com/hobbycity/store...idProduct=6563

BrianG · 09.28.2009, 04:23 PM

They would, but 7.2v (3.6v/cell peaked) is a bit high. I would add a diode in series with the pack to bring the max voltage to ~6.5v (I know this voltage is fine).

Arct1k · 09.28.2009, 04:45 PM

Whats the discharge curve on a duracell? they drop to 5.5v quick and i always end up replacing them early as don't want to die mid race / comp

BrianG · 09.28.2009, 04:57 PM

From what I remember, alkalines have a pretty linear discharge curve.

redshift · 09.28.2009, 07:00 PM

Well this probably only applies to a DX5, but run on 3 cells (~4.5V) the low battery alarm sounds. I did a rudimentary range test with a friend and the range seems to be around 4/10 mile, both on 3 AA and the full 4. Rx will not arm over 1/10 mile, but armed at close range the signal is good. I think I'll be sticking to AAs.. sigh.

Arct1k · 09.28.2009, 07:18 PM

Ok novak smart booster mentioned IIRC on 1S would appear to be the way to go...

http://www.teamnovak.com/products/sm...ost/index.html

Provides 6v and cuts off automatically when Lipo gets to 3.3v

redshift · 09.28.2009, 08:57 PM

That looks like a real good solution. Tower wants $40, that would buy a lotta AAs... but I have it saved.

Thanks!

BrianG · 09.28.2009, 09:12 PM

Yeah, the price is a bit steep IMO.

Since cost is not an option, what about this? Same pinout as LM78xx regulators too. All it would need is an LVC and it would be done!

BrianG · 12:27 AM

BTW, I just threw together my own 2s LVA. It is set to light an LED at anything under 6.8v (3.4v/cell), but I can adjust it for different values. Works good too. Circuit consists of 3 resistors, a pot, 3 diodes, and an LM324 comparator IC. Draws 24mA when the voltage is ok, and 35mA when the LED is lit. The circuit is a bit large, but I had to make do with what components I had floating around. I'd post a pic but can't find the cable to hook the camera to the PC. Grrr.

Don't know what I'm gonna do with it now. Guess it will just go into my "I'll use it someday" bin.

BrianG · 12:04 PM

OK, here is the LVA circuit. Sorry about the crappy pic, it was taken from my cell phone.

The battery is hooked to the red/black leads. The LED is connected to the black/white leads.

I can provide the schematic if you want.