Hello,
I need to sense the voltage of batteries(6 AA's in series), and to know when they are at 3vdc or so (maybe 2vdc) to drive a circuit that will flash a LED at about 1 Hz. Maybe with 555 timer and comparator. I am not sure where to start, or the most effecient way. Thanks for the help.
I don't know what to do from here. The sites help a little, but not much for someone who doesn't know what they are doing. lol This is all I have now. Can someone steer me in the right direction?
Ok, here is the thing. You want to detect when your batts drop to say 3V. You are also using batt voltage to power your 311. Problem is that the 311 needs +5v to operate, so when you batt dies so will your circuit. The other problem is that your also using your batt as your vref. When the batt dies so does Vref. The nice thing about the part Kchriste suggested is that it has built in Vref so the drop in batt voltage will not cause a problem. And the part is only 3 pins.
I think the LM139 operates down to 2vdc.
I would normally say about 0.8V per cell giving a total voltage of 4.8V for six cells. Rechargeables are more sensitive, ideally you need a coulomb counter but more practically speaking cutting the load at between 0.9V and 1V will do.
If he does the things that I have highlighted in red, the LED will be on until the voltage drops below Vref. I don't think that's what he wants. Of course, he really wants a flasher anyway, so an LED on the comparator output ain't gonna work anyway.
When voltage drops to 4.8 (as suggested), then blinking LED will blink. I was informed that the batteries would start at 6vdc and then normally operate at 4 vdc. I have not done my research to comfirm this. I am not sure if LM139 is the way I want to go. There is alot of unused gates.(room, power, and size are issues) Am I getting closer with this...?
If he does the things that I have highlighted in red, the LED will be on until the voltage drops below Vref. I don't think that's what he wants. Of course, he really wants a flasher anyway, so an LED on the comparator output ain't gonna work anyway.
After my last blunder, I am somewhat afraid to give out advice, but just one comment.
For U1, from the part number you listed, the device has an open drain output which means it needs a pull up and is an active low out.