How to measure voltage???

theJoseph

I had a really good basic plan for a solar powered robot that would search for bright light when it sensed that it need to, but I need a way to measure voltage and get that as a value back to the board, so it will know when it needs to charge.

I don't know much about this and I really don't know how.

any help would be great.
thanks

Mike Green

Look at EME Systems' website (www.emesystems.com). There's a link to app-notes and, on that page, there's a section on the RCTIME statement with examples of ways to measure voltages with a Stamp. There are also other examples in the StampWorks manual that you can download from Parallax (Support / Downloads / Stamps in Class Downloads) and in several Nuts and Volts columns that you can download from Parallax.

theJoseph

awesome. that is exactly what I need. a way to do it without buying a load of stuff.

thanks.

theJoseph

Ok
Now I'm considering more problems that I may encounter. (i'm still in the theoretical stage with my project.)

My idea is that when the robot senses low voltage, it will then find light meeting a certain threshold and stop. then the batteries will charge from the solar panels. BUT while there is power comming from both the batteries and the panel will it cause too much voltage to get to the BOE? I need to use a 6V battery and about a 6V input from the solar panel, i think.

ALSO, i think i need some sort of charge controller to prevent overcharging. but i can't find anything with a low voltage input such as my 6V panel.

is there any site or anything that can explain some of this to me?

Mike Green

Do some searching in the Wikipedia. Try a Google search with "wiki charge controller".

Bruce Bates

theJoseph -

Since this is purely theoretical, you may want to read about voltage regulators:
http://en.wikipedia.org/wiki/Voltage_regulator

Regards,

Bruce Bates

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Programming can't be all that difficult, it's nothing but 1's and 0's

Ugha

I know this is kinda a dumb suggestion... but why not use a photoresistor and rctime to check the light levels? You could
use four of them (one in each direction) to detect which direction is brighter and move the robot in that direction.

photoresistors are dirt cheap, and most of the parallax kits come with at least one.

allanlane5

+1 to "find the strongest light with photoresistors". You don't really want to use the Solar Cell to find the brightest light -- you'll never know what's "Brightest". But 4 CdS cells will let you find "brightest" fairly simply, then you can 'aim' the Solar Cell in that direction.

theJoseph

yeah I've gotten light seeking down pretty good. I use two photoresistors. but i could improve it once I get it set up and use more to more accurately tell where the light is comming from by using more. it's pretty cool. I've programmed it to just stop when the light reaches a certain threshold. (the recharging part) but of course I don't have my solar cells yet. i was just working out the program.

MORE SOLAR/ELECTRICAL QUESTIONS
I was thinking about using .1C to trickle charge the batteries as the robot just sits there. this is much more simple than other types of charging because it doesn't require a charge controller. (if this is a bad idea someone say so, but i can't find an approprite charge controller or solar panels capable of putting out descent currrent with 6V) a paper I read said that the boe bot's current drain is 300 mA.(is that accurate??) so if i use a 300 mAh battery does that mean that I need panels that produce 330A? (Boe-Bot's current + .1C of Battery)
as i said before I don't know much about electronics but this seems reasonable to me.
when I get this one issue cleared up I'll be ready to start

Mike Green

I suspect that the quoted current drain is an average while the BoeBot is active. If you stop sending servo pulses to the motors, they go into a low power mode and the Stamp itself draws only a few mA. You might invest in a $15 multimeter and actually measure the current with it.

What you would like ideally is to have a solar panel that produces more current than the BoeBot draws when idle. It's that current that has to be less than the 0.1C of the batteries. The panels also have to be able to put out more voltage (when producing the charging current) than the battery produces. Good NiMH AA cells these days will have 2300-2700 mAh capacity which means that the 0.1C rate is 230-270 mA. If you have 5 cells (to produce 6V), you'll need a solar panel that'll produce about 1/4A at over 6V, so you're talking about at least a 1.5W panel. You don't need a charge controller because the panels won't produce more than about 0.1C and the BoeBot is drawing some of that current at idle. Don't forget that you'll need a series diode to prevent the BoeBot's batteries from discharging through the solar panel when the light level is low and that diode will cause some voltage drop (about 0.7V). Your panel should produce about 250mA at about 8V to allow for the diode and the peak battery voltage so it will be a 2W panel. The batteries will load the panel down to reduce the voltage to the 6-7V range.

Post Edited (Mike Green) : 3/16/2008 5:23:24 PM GMT

MSDTech

You might look at the 16533 panel at http://www.siliconsolar.com/oem-solar-panels-p-16185.php

I had this hooked up through a diode to a 5cell NiMH battery pack (2300 mha) for a week on my back porch to see if it would be adequate to power a weather station I am building. I've attached the board layout and the results of the testing. It seemed to work well, but I determined I would need a larger battery to allow for several days of clouds and snow.

The first four days were clear and sunny, but the last three were overcast and raining. The final day did have a little sun, but not enough to recharge the battery to a level that would last the night. Based on the final days of the test, I determined that the 2300 mha would not be adequate to keep the system going. The final battery selection was a 10000 mha battery (http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=1482). This unit also has a built in thermal protection switch which will disconnect the batteries if they start to get overcharged.

I've also attached the code to read the battery and solar panel outputs. U1 and U2 are ADC0831 and the bluetooth connection was a A7 eB501-SER.




Post Edited (MSDTech) : 3/17/2008 12:08:41 PM GMT

sam_sam_sam

MSDTech

That look real nice

You have this Project·layed out very well and you done your home work on your Project

Thank You for the link for the Solar Panels I sure can use some of those panels

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··Thanks for any··that you may have and all of your time finding them

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Sam