View Full Version : Battery Voltage Drop Detection

11-22-2009, 07:02 AM
I am powering a Basicstamp1 directly(no regulator) with a 9Volt alkaline battery andˇsame batteryˇis driving a H bridge to run a DC Latching Relay. When the battery voltage drops to about 6 volt I want Basicstamp not to drive H brige anymore. I tried to use a zenner diode to detect voltage drop but I havent been successful yet. One of the problems I have, I dont know what are the voltage limits for an Input Pin, I mean at what voltage it is 1 and 0. If zenner diode doesnt work is there anyother way to detect voltage drop.



11-22-2009, 11:37 AM
I must assume you mean you are using the Stamp's onboard 5V regulator in lieu of an external regulator, as you will fry the Stamp on 9V connected to Vdd. That said, you should be able to use a simple voltage divider to feed the right voltage into a stamp input pin. The pin's transition voltage from high to low is about 1.4 (YMMV) so I calculate two resistors, 3.3 K and 1K or multiples thereof. Put them in series, the junction goes to a stamp input pin through a 330 ohm protection resistor. The single end of the 1K resistor to ground and the single end of the 3.3K to your positive battery supply (+9V).

Keep checking the pin in software, as long as it is high, you have 6 volts or more. Low means under 6V.

ˇ"If you build it, they will come."

11-23-2009, 08:00 PM
Roni, I believe what you want to use is a voltage comparator, check out the many tutorials and resources on the web, here is one to get you started
home.cogeco.ca/~rpaisley4/Comparators.html (http://home.cogeco.ca/~rpaisley4/Comparators.html)