Developing a "clock/thermometer/battery charge level"

[ioan]

My teardrop it's almost done and June 7-11, Grants Pass, OREGON "TearJerkers Birthday Bash 2012" it's going to be our first official trip.

Now that my current pet project, the teardrop, it's almost finished, I'm thinking of the next one. Would anyone be interested in a "clock/outside thermometer/battery charge level", all in one, DIY kit? I can design it and test it and maybe sell the kits or publish the design and software, if you want to build it from scratch.

The cost of the parts would be somewhere around $60:

It's going to need:
LCD screen: http://www.sparkfun.com/products/790
Real time clock module: http://www.sparkfun.com/products/99
A brain: http://www.sparkfun.com/products/9061
Waterproof temperature sensor http://www.sparkfun.com/products/11050
A 16MHz ceramic resonator, few caps, resistors and a custom PCB.

Any thoughts?

[absolutsnwbrdr]

Don't even get some people around here started on battery charge level. To some, it is an impossible task to determine it unless you spend $1,500,000 on the electronics, then do a feasibility study taking into account the ambient temperature of the nearest guinea pig, the ph level of the most recent rain, the earths rotation, the magnetic force of a navel orange, etc...


But yes, I'm definitely interested to see what you come up with

[ioan]

Don't even get some people around here started on battery charge level. To some, it is an impossible task to determine it unless you spend $1,500,000 on the electronics, then do a feasibility study taking into account the ambient temperature of the nearest guinea pig, the ph level of the most recent rain, the earths rotation, the magnetic force of a navel orange, etc...


But yes, I'm definitely interested to see what you come up with

The battery charge level it's pretty straight forward. The ATMega328 processor's analog pins can read an analog value for the voltage and return a number between 0 and 1023. 1023 occurs at the voltage that ATMega328 is running on, 4.9v. I would need to use a voltage divider to get the 12v in that range: http://en.wikipedia.org/wiki/Voltage_divider

That means 12v/1024 = .0117v increments, so charge level would be pretty accurate.

Edit:
So for example, if I get the values for the resistors in the schematic from wikipedia: http://en.wikipedia.org/wiki/Voltage_divider
Z1 = 10k ohm
Z2 = 330 ohm
With this setup Vin can go up to 32.2V and your ATMega328 will be able to tell the voltage in .0314 volts increments

[Treeview]

This is just my way of looking at this...

Clock...daylight or dark...hungry=meal time
Temp...comfy...enough clothes...not comfy=more or less clothes
Battery level...store bought solution

Tom

[parnold]

Zach: So negative just because someone didn't like your $14.00 volt meter.

I'd be interested in seeing what you come up with too!

[Shadow Catcher]

The difficulty of just monitoring the voltage is that if it is under load it is not particularly accurate. This brings up to what is, "enough". There are a number of us that for one reason or another want to have an accurate profile of use and charging, goes into and goes outa and we tend to be more intense in our usage i.e. our WACO refrigerator TV etc. and solar panels input.
If you only use your trailer a couple of times a year for Tearjerkers gatherings (not a bad thing and a whole lot of fun) your battery will age out and going below 50% DOD is not a concern. Our trip to California will be the better part of a month (one of the advantages of being married to a teacher, June, July, August), and the National parks don't have electric.
I opted for a Vectron battery monitor, way less than $1,500,000.
Our "atomic clock" has indoor and out door temp sensors.

[ioan]

I opted for a Vectron battery monitor, way less than $1,500,000.
Our "atomic clock" has indoor and out door temp sensors.

Well, I don't like to buy stuff that I can make myself. There is no fun in just going to walmart to buy every time I need something. I really don't care if my solution is not as good as a $200 device... for me is more important having fun building it. When you build it, there is a story to share behind the thing and that's important when someone asks you "what's that?" :-)

[Treeview]

There is no fun in just going to [The Portal to Hell] to buy ... for me is more important having fun building it. When you build it, there is a story to share behind the thing and that's important when someone asks you "what's that?" :-)

Agreed!

That's why I'm building a camper out of a truck like this:

http://stonerradiator.com/images/dsc00667.jpg

instead of buying a Toyota Chinook or similar.

I'll be interested to see what you come up with for the battery monitor portion.

Tom

[Shadow Catcher]

That is why I made the point about, what is enough! In my effort to not exceed my level of incompetence I stay away from electronic DIY. I am comfortable doing electrical work, which is with in my competence.

[bdosborn]

Clock,voltmeter,thermometer

Something like this is hard to beat *unless* your meter monitors amp-hrs in and out like a true battery monitor versus just voltage. That would be very interesting.

Bruce

[absolutsnwbrdr]

Zach: So negative just because someone didn't like your $14.00 volt meter.

Sorry Paul. Couldn't help myself

Clock,voltmeter,thermometer

Something like this is hard to beat *unless* your meter monitors amp-hrs in and out like a true battery monitor versus just voltage. That would be very interesting.

Bruce

Thats a nice little package deal Bruce. But isn't the DIY so much more fun? We all could have gone out and bought campers, but yet many of us opted for the fun route. I agree $10 is hard to beat, but wheres the fun and satisfaction?

[bdosborn]

Thats a nice little package deal Bruce. But isn't the DIY so much more fun? We all could have gone out and bought campers, but yet many of us opted for the fun route. I agree $10 is hard to beat, but wheres the fun and satisfaction?

I've obviously got no issues with DIY (since, like you, I built two trailers). But spending $60 and time on a $10 voltmeter doesn't seem fun or satisfying to me. However, spending $60 and time on a *battery monitor* that usually cost $160 and upward, well, that's different. Then it's another way for me to stick it to the man.

FWIW, everyone is different and I'm the last guy to tell anyone they *shouldn't* DIY, the project as presented just doesn't appeal to me.

Bruce

[ioan]

But spending $60 and time on a $10 voltmeter doesn't seem fun or satisfying to me. However, spending $60 and time on a *battery monitor* that usually cost $160 and upward, well, that's different.
Bruce

The difference between the project I'm talking about and the $10 voltmeter is that you can make it do whatever you want. ATMega328 processor has 23 I/O lines that can be used for whatever... start your AC when it's too hot, control the vent's fan speed, scratch your back... etc. You can add features until you used all the I/O lines and even then, you can use a shiftregister to get many more lines.

Making it to measure the battery current it's not hard either, the only thing is needed is a very low resistance shunt (current sense resistors, under $10), run your current thru it, measure voltage across and:
current (i) = voltage (v)/shunt resistance (r)
power in watts is then i^2 x r, or v^2/r, or i*v

... and because you are using a processor (think of it as a small computer in one chip) you can log the values, calculate peak times, etc.

That being said, I agree, it's hard to beat that $10 product from amazon.

[parnold]

Open the pod bay door HAL.



Reminds me of the time I built a voice synthesizer for my Atari 800XL computer back in 1985. Boy that was fun.

[bdosborn]

The difference between the project I'm talking about and the $10 voltmeter is that you can make it do whatever you want. ATMega328 processor has 23 I/O lines that can be used for whatever... start your AC when it's too hot, control the vent's fan speed, scratch your back... etc. You can add features until you used all the I/O lines and even then, you can use a shiftregister to get many more lines.

So here's a 100 amp shunt:


Shunt Linky

Current direction is indicated by the sign (+ or-) of the voltage across the shunt and 50mv across the shunt=100 amps. You'll need another sample point to get battery voltage. Every second or so would probably be a fast enough sample rate and the processors has a a 6-channel 10-bit A/D converter so two sample points is no problem. I wonder what the voltage range of the A/D converter is? Can you get the processor with an on-board 12V power supply? What would you use for a display? You can worry about Peukert's equation later.

Hmmm

I bet a lot of people would build a battery monitor. I'll build one if you get it running and check it against my Trimetric.

Bruce