monitoring battery voltage

[mana111]

hi
i'm doing a battery powered project which i need to monitor the battery and give an indication when it's low
what is the best method to do it?
i'm using 9 volt battery and the low voltage is 7
thanx in advane

 

[IanP]

You can realize voltage sensing in one million and one ways ..
On of the simplest methods of sensing voltages is by using a zener diode ..
Here are examples:
"ZENER-RESISTOR VOLTAGE SENSING"
**broken link removed**

Regards,
IanP

 

[ehsanelahimirza]

normal voltage sesors are available in market

u can use a digitalone

u have to use and gate or nand as u prefer.
1 terminal coming from battery through a resistor to show that battery is working
and other from digital or other voltage sensor which would produce a low or high signal at 7 volts.

this can be done also without using any sensor just use resistors so that above 7V resistor is providing a signal to IC which is high and when voltage is dropped from 7V IC should feel low

 

[Tohu]

Hi, you can use simple comparator, like a LM393, all is depending from this do you have some available part in your circuit that can be used. The diagrams from IanP is good, but have one big disadvantage, the LED is on when the voltage is in nominal range. There are two problems:
1- Via the led you will have a current that will be extra load, and discharge your battery
2 - The human is more sensitive to light on, but in this case you will have light off on event.
How IanP say, you have many different ways, if you can be a more specific, we can help you.

 

[mana111]

hi
thankx all
i really dont know what to choose iheard that there is ics that can do it but it's not in my country.

i need solution that is simple and of course does not draw a lot of current because this is another problem

could you give some schematic ehsanelahimirza
and another quistion for the comparator what am i going to compare the battery voltage with?? i have only one voltage source and it's from the battery.
i really dont get it could you explain please
thanx alot for your efforts

 

[Tohu]

Hi,
The battery voltage and reference device. For reference voltage you can use some chip like TC431, but you need this precision device. My suggestion is a zener, 4.7 V for example. If your alarm level is 7 V, then you must have a divider 7/4.7~1.48 or you can use the 4k7 and 10 k for the divider. To prevent battery discharge you can use high resistance diodes, for example 47 k and 100 k.

 

[ehsanelahimirza]

i need solution that is simple and of course does not draw a lot of current because this is another problem

could you give some schematic ehsanelahimirza

i told u to use a resistance by such a value that is giving too much voltage to the IC that should take it as high.but now when voltage drops to 7V . resistance is allowing only that much voltage that is taken as low by IC.u r going to use simple AND gate IC.usually the voltage IC takes as high level is 2.5V.so u have to take a resistance that when battery is at 8V, resistance is giving only 2.5(u have to check it may varry) to IC and when voltage drops to 7V, 2V are given to IC and it will take this as low