Piezospeaker and Low Battery

addy

·hello
Can someone help me please? For my senior design project, I wanted to sense if there is low battery on the boe-bot and if so I want the piezospeaker horn to go off and then I will connect my bluetooth to it to control it and bring it back to the base station for a new battery. What pin on the Board of Education board will allow me to see when the batteries are low or any other suggestions are allowed. Thank you so much for your time in advance.

Chris Savage

Please have a look in the BOE-Bot manual where the Piezo and how it works is covered.· This will explain how it is used to detect low batteries.

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Chris Savage
Parallax Tech Support
csavage@parallax.com

Bruce Bates

Addy -

First you will need to define what you mean by "low battery" as this can have meny meanings. You may mean a certain low water voltage limit, or you may mean some number of minutes or hours of use depending on the battery source and the ampere hours consumed.

The usual method for sensing battery voltage is to use an ADC (analog to digital converter) across the battery terminals and sample it on a regular basis. The low water limit is maintained as a constant in the PBASIC program, and compared to your continuing voltage readings. If/when that low water occurs, you execute whatever appropriate routine you choose to execute. Just remember that driving a piezo element, using a diminishing battery, may well be a self-defeating action.

The usual method for checking the instantaneous amperage draw is to place a small resistance, high wattage resistor in series with the positive battery lead. You then check the voltage drop across the resistor, and using Ohm's Law you can determine the instantaneous amperage draw. You will also need an accurate source of time, such an an off-board RTC (real time clock). You then take continuing current samples over periods of time, to build a table of battery draw-down, or to compute a mathematical average of current (ampere-hour) depletion. This will permit you to estimate the ampere hours consumed, and thus the ampere hours remaining in the battery.

I hope that gives you the basic idea.

Regards,

Bruce Bates

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Post Edited (Bruce Bates) : 4/26/2006 3:17:33 PM GMT

addy

I was meaning the low water limit but I didnt know what it was called, but I dont have an analog to digital converter and my prototype is due monday...so I wont have time to implement that. But thanks because that can go into the future recommendation section of the report.