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GrandRC . CanoMod . Futaba-RC

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Off Topics > Question for you electronic wizards:
 
 
rob_jones
Key Veteran
Location: Oglethorpe, GA

I want to build a simple electronic gizmo, but I have a very limited background in electronics. And I have no clue how to design my own circuit.

Does somebody know of a resource where I can get instructions on how build a simple LED voltage meter? One that will, say, light a green LED if the voltage is greater than 1.2, orange if it is equal to 1.2, or red if it is less than 1.2.

I am going to need step by step instructions that list the specific parts needed. Or as close to step by step as I can get. Basically, if I am left to figure out anything on my own, I'll never get it to work.

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Team MRC Hirobo
I reject your reality and substitute my own.
02-16-2004 Over year old.
 
 
sixeven
Senior Heliman
Location: Ft. Myers Florida

Step 1: Get phone

Step 2: order Voltwatch.

Seriously, it will cost you 10x as much in individual parts from Radioshack or the like and way more time and effort than nessesary to build that circuit.

A Voltwatch does exactly what you are trying to build and costs less than 10 bucks.

SiXeVeN
02-17-2004 Over year old.
 
 
Sar
Elite Veteran
Location: Kingston, NY

The power supply for this circuit will be 1.2 volts, possibly less, correct? Or will the LED portion of the circuit be externally powered by a higher voltage?

The reason I ask is that most LEDs require over 1.2 volts to operate, so you are then faced with the challenge of having to 'step up' the voltage to power the LED, which requires additional electronics. Which will complicate this kind of project a bit more.

If a seperate higher voltage power supply is available, then the job becomes very easy.

A voltwatch doesn't work on single cells.

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Jon
02-17-2004 Over year old.
HOMEPAGE  
 
 
sixeven
Senior Heliman
Location: Ft. Myers Florida

My eyes....them going crazy....I can't see so good.

Sorry, should have actually paid attention to the voltage numbers in the post. Still, considering the cheap and simple analog meters out there, why waste the time and effort?

SiXeVeN
02-17-2004 Over year old.
 
 
Dragon2115
Key Veteran
Location: New England

Here's a place you can start.

http://www.national.com/ds/LM/LM3914.pdf

The LM3914 is at the heart of most LED type voltage monitors. On page 10 of the pdf is the schematic for a 4.46 - 5.56 expanded scale voltmeter. You can substitute a 9 volt battery and a resistor for the transformer in the upper right. The text should explain how to vary the resistor values around the chip to get the range you want.

Btw, if you were going to use this on an rx pack you could self power it off the pack being measured. Where you want to look at something much lower you will need to use an external source of around 5 volts. A 9 volt is just convenient.

The LM3914 is available from Allelectronics.com for $1.75

They're kind of like the Building 19 of electronics so stock comes and goes. I made one of these meters for checking rx packs for about three dollars.
02-17-2004 Over year old.
HOMEPAGE  
 
 
Sar
Elite Veteran
Location: Kingston, NY

There are voltage boost chips such as
http://www.national.com/ds/LM/LM2623.pdf

which can be useful, unfortunately this is the lowest input I could find, and it requires 1.1 volts to start, but once started will run down as low as .8 volts.

The chip will produce up to 14 volts from one 1.2 volt cell.

--
Jon
02-17-2004 Over year old.
HOMEPAGE  
 
 
Dragon2115
Key Veteran
Location: New England

That's true, but if he isn't familiar with them, setting up a boost mode switcher properly might be a little tricky. That was why I suggested the battery so it wouldn't get too complicated.
02-17-2004 Over year old.
HOMEPAGE  
 
 
warrior29
Senior Heliman
Location: FL

The use to be a magazine out called popular electronics that would have project circuits like this you could build but I haven't seen it on the shelves in a while.
But by the time you make the circuit board buy all the parts and put it together you will spend more than the cost of a voltwatch.

Credit card can't be max'ed I have more up grades to buy!
02-17-2004 Over year old.
HOMEPAGE  
 
 
rob_jones
Key Veteran
Location: Oglethorpe, GA

A lot of this is over my head, but I think I can get started.

Basically, I'm not doing this to save money or find a cheaper way to make something I could just buy. C'mon guys, we fly RC helicopters. Since when do we look for the easy way to do something?

I like the challenge of trying to do something new. I want to build a glow driver with an LED indicator that shows that A) the unit is switched on, and B) the glow plug is glowing. I figure the three LED's will show battery strength and that the plug is good.

I have a version that I've already made that uses an analog meter from a Du-Bro glow driver. It works okay, but I really want to try to make an electronic one.

I know I could just buy a RadioSouth Pro Driver. But then again, It's winter and I haven't gotten to fly in a month, so that's not the point.

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Team MRC Hirobo
I reject your reality and substitute my own.
02-17-2004 Over year old.
 
 
rob_jones
Key Veteran
Location: Oglethorpe, GA

Could something like this be modified to work on 1.2V?

http://www.solorb.com/elect/solarcirc/vom/

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Team MRC Hirobo
I reject your reality and substitute my own.
02-17-2004 Over year old.
 
 
Sar
Elite Veteran
Location: Kingston, NY

You would still need a voltage booster to power the chip, or an external power supply. The 3914 is a great chip, but requires at least 3 volts to run it. If you want to power an IC(integrated circuit), you need to bring the voltage up.

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Jon
02-17-2004 Over year old.
HOMEPAGE  
 
 
nheather
Veteran
Location: Horsham, West Sussex, UK

BimmerM3

Maybe, but way over-engineered.

You could do what you want with

2 comparators (a single 8 pin IC)
A 1.2V reference (cheap = zener diode + resistor, better = reference IC)
A tri-colour LED and two resistors

As Sar pointed out, the problem is that it could not use the glow driver as the power source because LEDs need at least 2V to operate.

I reckon the parts would be somewhere between 5 and 10 dollars.

Cheers,

Nigel
02-17-2004 Over year old.
 
 
rob_jones
Key Veteran
Location: Oglethorpe, GA

Hmmmm, I hadn't considered a tri-color LED. I like that idea.

What if it used a 3V lithium battery to power the LED's, and then 2 or 4 NiCad's in parallel to light the glow plug?

nheather: Got a schematic?

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Team MRC Hirobo
I reject your reality and substitute my own.
02-17-2004 Over year old.
 
 
nheather
Veteran
Location: Horsham, West Sussex, UK

BimmerM3

Just off to bed (11pm in UK) - I'll try and spec something out tomorrow and send it to you.

Cheers,

Nigel
02-17-2004 Over year old.
 
 
rob_jones
Key Veteran
Location: Oglethorpe, GA

Nigel,

Quote 
I'll try and spec something out tomorrow and send it to you.


That'd be fantastic! Thanks for the help!

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Team MRC Hirobo
I reject your reality and substitute my own.
02-17-2004 Over year old.
 
 
Sar
Elite Veteran
Location: Kingston, NY

If you wanted to go a little nuts, you could build a supply that uses four NiCds cells wired in series (for 4.8 volts) then build a cheap PWM(pulse width modulation) glow driver around a 555 timer IC driving a mosfet. Then incorporate a voltwatch or a 3914 for power level (you can also do this with zener diodes if you want to eliminate an IC). PWM driven glow drivers have the advtange of being able to adjust the current on the fly with a potentiometer if you wanted. Just throwing out ideas since this thread is about making a glow driver.

--
Jon
02-18-2004 Over year old.
HOMEPAGE  
 
 
Dan C
Senior Heliman
Location: Barnsley, Yorkshire

whts wrong with using a 3V button battery in the beast remember you are only comparing against 1.2V so you don't need to limit the units power supply to 1.2V

get a button cell use it to drive a comparator and drive the led from the comparators output,
Maybe have to look at current drawn from the button cell by the led but I can see it lasting a fair time
02-18-2004 Over year old.
 
 
nheather
Veteran
Location: Horsham, West Sussex, UK

BimmerM3

Sent a PM.

Cheers,

Nigel
02-18-2004 Over year old.
 
 
rob_jones
Key Veteran
Location: Oglethorpe, GA

Got the PM, thanks Nigel!

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Team MRC Hirobo
I reject your reality and substitute my own.
02-18-2004 Over year old.
 
 
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