Need some electronics help

[Tufiremn]

What would it take to make an LED flash when the voltage dropped below a certain level? Kinda like the LED on a Revvy x-board. I know someone on here has this info.

[athomas]

That's an easy one. You would need an op-amp comparitor circuit and a timer and of course the voltage regulator for the circuit.

1. Regulate the voltage to 5v (that way you will always have sufficient voltage to power your circuit and provide a constant comparison voltage.
2. Build an op-amp comparitor circuit. Connect one input of the comparitor to the 5v as your comparison voltage, because it will be constant.
3. Connect your battery voltage to the 2nd comparitor input through a voltage divider network of resistors. This will bring the voltage down from 18v to a useable 5v range. Example: If you want your battery voltage to be flagged at 15 volts, then the ratio for resistor values of the voltage divider should be calculated as 5v/15v = R1/(R1+R2) where R1 is the resistor from the comparitor input to logic ground and R2 is the resistor from the same comparitor input to the voltage source.
4. Connect the output of the comparitor to the input of a 555 timer circuit in a configuration so that when activated the output will flash at a predetermined rate.
5. Connect an LED to the output of the flasher.


I would draw a diagram but I don't have a scanner handy to put it on.

Hope this helps get you started.

[314159]

it gets easier than that,

they make these devices called low battery indicators. they are packaged much like an led, when the voltage drops below a certain point. the led goes on.

check out www.digi-key.com for part numbers 67-1195-nd,67-1196-nd,67-1193-1-nd, and 67-1194-a-nd.

they have some fixed voltage ones that operate at 2.5v and they have some adjustable ones for 3.75-7.5 volts. if they don't have the voltage you want, you can feed the device off of the output of a voltage devider. because voltage drops on series resistors are proportional.

------/\/\/\/-----|------/\/\/\/------
gnd____1k ohm_____|________5k_______source voltage
__________________|
_________________output

the voltage on the output would be 1/6 of the source voltage in this case. just devide up the sorce voltage to make the low battery indicator turn on when you want.

because of the discharge curve of batteries, there is not a significant drop off in voltage till they have consumed about 90% of their resources, this might give you a warning too late.

you could use a microcontroller with an analog to digital converter built in with a typical battery discharge curve in a table, or just have it go off of certain voltage incremints, and have this drive a bar graph type display to give you a more accurate picture of your battery condition.

[zvanut]

like an LED, will these drain the power of a battery noticeably?

keep talking, im intrested

[athomas]

These circuits will have some power drain, but will be small compared to the circuits used by the devices you are monitoring the batteries for. Essentially the power drain will be not noticable. Once you notice the low power indicator turn the circuit off to prevent further drain on a low battery. The LED indicator will drain more power than the circuit controlling it, which is still much less than the motor on an agitating hopper.