[NBR] - DIY Electronics Project - Any Interest?

[charlie55]

Hi all:

I've been puttering around during my self-imposed winter down-time, and have come up with a battery/charging system monitor circuit that might be of interest to some of the electronics DIYers on the forum. It's a variation on some similar circuits already available on the web that uses a single tri-color (RGB) LED to indicate the state of your electrical system. While the threshold voltages are fully adjustable, the basic display is:

Red - 0 to 12.6 volts (ostensibly means that the battery's draining)
Blue - 12.6 to 13.6 volts (battery at nominal voltage)
Green - 13.6+ volts (battery charging)

I've done up a prototype and bench-tested it successfully. Draws about 25-30 ma (max) and can be fit onto one of those Radio Shack 1.5 x 1.5 perfboards. Most of the parts are junkbox recycled, and I'd ballpark the whole project as coming in at less than $15.00.

I know that you could just do a "cheap and easy" and toss an automotive voltage gauge onto the scoot, but I thought that some folks might get a kick out of this.

[Lostmycage]

That's awesome! I'd love to see more.

What size is the LED module. I'm curious as to whether it could be mounted on the dash (would require drilling and probably silicon sealing it into place) but it's make a nice neat integrated mod and a way to monitor the charging system.

[charlie55]

Well, I'm a lot like the circuit - strictly analog. Consequently, I don't have a digital camera for pics. May be able to borrow one from a co-worker though.

In so far as size, my prototype fit's on one-half of the following RadioShack board, so it's about 1-3/4" square:

http://www.radioshack.com/product/index ... Id=2104052

Since I can't etch my own boards, I had to do the prototype with point-to-point wiring, so it's probably larger than it really needs to be. My eyes ain't as good as they used to be, so I can only go so far with miniaturization

I was toying with the idea of making it an integral part of the gauge cluster, but I've decided that I'll most likely fit it into a case of some sort and velcro it to one of the flat spots on the headset that covers the brake fluid reservoirs. One thought would be to gut one of those little plug-in wall transformers, fit the board to it, then use the integral low voltage (output) wires to do the power hookup.

I should be putting the finishing touches on the circuit schematic and parts list over the course of the next few days.

[kschulz]

Cool - I'm interested. Looking forward to seeing what you've got.

[bigbropgo]

scooter attack has something like this. its the only one i have run across. i think its pretty sweet that you made one though.

[jmkjr72]

there are a few guys over on zuma forums with the z125 that have some thing like this installed as they have a shit ass charging system that cant keep up to the dual head light load
and i think they spent less then 25 bucks to get the part

[charlie55]

Well, for whoever is interested, here's a simplified schematic, parts/cost list, and instructions:



Parts List:
=======
D1 - 1N4001 1 Amp Rectifier Diodes (RS 276-1101) $0.99 (2)
VR1,VR2 - 10K Ohm 15 Turn Trimmer Pots (RS 271-343) $2.69 (ea)
C1 - 100uF 50V Electrolytic Capacitor (RS 272-1044) $1.49 (ea)
R1 - 220 Ohm 1/2W Carbon Film Resistor (RS 271-1111) $0.99 (5)
R2 - 2200 Ohm 1/2W Carbon Film Resistor (RS 271-1325) $0.99 (5)
D2 - T1 3/4 5mm Full Color LED (RS 276-028) $2.99 (ea)
U1 - LM158 Dual OpAmp Nearest Equivalent TL082 Dual JFET OpAmp (RS 276-1715) $1.99 (ea)
U2 - 78L05 Fixed 5 Volt Regulator (TO-92 Package) Nearest Equivalent LM7805 (RS 276-1170) $1.59 (ea)

So, if you need to purchase all of these parts, they'll run you about 15 and a half bucks. However, since I'd assume that most folks interested in this type of project already have a stash of junk-box parts on hand, the actual cost would probably be much less. Additionally most of the part tolerances are really not that critical, so you could, for example, use a 270 or 330 ohm resistor for R1, a 50uF cap for C1, etc. If you substitute other components for U1 and/or U2, however, please be advised that the pinouts could change as well.

Of course, if you don't have a soldering iron and all the necessary paraphernalia, then that'll add to the cost as well. In so far as the construction, I used one half of a dual 213 hole mini board (RS 276-148) that goes for $1.99

Circuit Description:
===================
As this circuit does not have an on/off switch, power must be provided via a connection to a switched source (the ignition switch, for example) so as to prevent the battery from being slowly drained over time. A suitable connection to ground (such as the battery's negative terminal is also required.

Diode D1 serves to protect the circuit from damage should its power leads be accidentally connected to the wrong polarities.

Capacitor C1 serves to provide some power smoothing (ripple reduction). The power is then fed to potentiometers VR1 and VR2, as well as to operational amplifier U1 and voltage regulator U2.

Potentiometer VR1 controls the voltage at which the RED component of LED D2 turns OFF, while potentiometer VR2 control the voltage at which the GREEN component of that LED turns ON.

The output of voltage regulator U2 (a constant 5 volts) is fed to operational amplifier U1 where it is used as a basis for comparison to the voltages from potentiometers VR1 and VR2.

The regulated 5 volts from U2 is also fed (via current-limiting resistor R1) to the common anode of LED D2. This is what provides the actual power to all three of the LED's color components.

Resistor R2 serves to reduce the intensity of the LED's BLUE component so that it is, from a visual standpoint, OFF whenever either of the other two color components is ON.

Calibration:
===========
I believe that most of our scooters use AGM-type sealed batteries that typically measure between 12.6 and 12.8 volts, fully charged, with no load. I measured mine while it was on my workbench, and it indeed proved to be 12.6 volts. Additionally, even though our scooters have 12 volt electrical systems, the actual voltage coming out of their regulator/rectifiers is usually something in the neighborhood of 14 to 14.5 volts. Taking these two factors into consideration, I decided that I'd set up the circuit's color transitions as follows (YMMV):

0 to 12.6 volts: RED - Charging system or battery problem (totally not charging)
12.6 to 13.6 volts: BLUE - Possible problem, but could be normal under excessive load or when idling.
13.6+ volts: GREEN - No problem, battery charging properly.

Now, the circuit's calibration is pretty straightforward, but requires a variable voltage source and a voltmeter (if the source doesn't have one built-in:

1) Set the voltage source down to zero and turn it off.
2) Connect the circuit to the voltage source (observing polarity).
3) Turn the voltage source on and adjust it to the voltage at which you want the RED portion of the LED to turn OFF.
4) Adjust VR1 up or down until the RED portion of the LED just turns OFF.
5) Now set the voltage source to the voltage at which you want the GREEN portion of the LED to turn ON.
6) Adjust VR2 up or down until the GREEN portion of the LED just turns ON.

Providing that you've set up your threshold voltages far enough apart, you should see the LED transition RED-BLUE-GREEN as you increase the voltage source from 0, and GREEN-BLUE-RED as you then decrease the voltage source to 0. (Actually, the circuit doesn't really light anything up until there's about 5 or so volts applied to it since the voltage regulator (U2) requires that as its minimum operating voltage. However, if your electrical system has reached the point where it can't even crank out 5 volts, you won't need a little red light to tell you that something's seriously wrong.)

Disclaimer:
==========
I assume no responsibility for any damages or injuries resulting from the construction and/or use of this circuit, whether that construction proves to be faulty or not. This circuit is presented merely as a DIY project, and the consequences of its use or misuse lie solely upon those individuals who choose to do so. That being said, I've run the sucker up to 20 volts and
I've still got most of my fingers left.

Questions:
=========
If you've got any questions, observations, or suggestions pertaining to this circuit and/or its description, please feel free to get in touch with me. I've been married for 22 years, and working at the same job for 17, so nothing you could say or do would have even the slightest impact upon my self-esteem.[/img]

[Lostmycage]

Charlie, that's cool! Any chance you could borrow a friends digital cam to snap a pic? I'd like to put this in the DIY section.

[babblefish]

Being a DIY geek myself (and having an electronics degree doesn't hurt either), I think your circuit is pretty cool. As a matter of fact, that basic circuit could be used as the front end of an intelligent battery charger by using the LED output signals to drive a 12-14 volt charger circuit - basically nothing more than a 1 or 2 amp DC power supply. Of course, unless you have a lot of spare parts in your junk box, buying a Battery Tender may be cheaper.

For the non-geeks out there that would like some sort of on-board voltmeter that doesn't cost a lot, Hobbico (p/n HCAP0331) makes a 12 volt meter that costs around $10 and can be bought or ordered through any hobbyshop (support you local hobbyshop!) or can be ordered through www.towerhobbies.com.

[charlie55]

Thanks.

This circuit could also be modified to use three discrete LEDs (Red-Yellow-Green), or you could even just chop out the "blue portion" and go with a discrete Red and Green being driven off the opamp. You could then set the voltage trigger thresholds such that they indicate a simple go/no-go situation.

If you look on ebay, there's tons of digital readout LED volt meters for about 10 bucks that work completely off the scoot's power (i.e., don't require a separate battery for their 5 Volt supply). For example:

http://cgi.ebay.com/ebaymotors/Red-LED- ... 2558849042

Me, I just like to putter around and waste time re-inventing the wheel.

[kschulz]

Nice little circuit Charlie - clean and simple. Thanks for sharing.

[charlie55]

I've made a change to the circuit and modified the schematic and description in my earlier post. Diode D2, which ostensibly controlled the blue portion of the LED, has been replaced with a 2.2K Ohm resistor. The reason is that, during testing in a well-lit room, it became apparent that there was too much "blue" while the green component of the LED was on. This part substitution results in a "greener green" while minimally diminishing the intensity of the blue.

BTW: Hope to have a test-bench demo video available today or tomorrow.

[charlie55]

OK, finally have a video demo of the circuit in action:

<embed width="600" height="361" type="application/x-shockwave-flash" allowFullscreen="true" allowNetworking="all" wmode="transparent" src="http://static.photobucket.com/player.sw ... emon-1.flv">