Super Capacitor\Cell Battery Voltage meter

[Vinco]

Trying ti find a circuit to have 5 leds for examples to indicate the voltage on a cell battery or capictor. The power for the circuit must come from the battery\capacitor.

Any ideas, the voltage will range from 1 to 3v.

 

[kpatz]

You'll need a fixed voltage reference to compare the battery voltage to, and to drive LEDs you'll likely need a boost converter otherwise if the battery is below 2V or so the LEDs won't light.

If you use a boost-mode switching regulator it can also serve as the reference voltage source. If your battery voltage is 1-3V that's a 2V range, with 6 levels to measure (assuming the lowest is no LEDs lit and the highest is all 5 lit). That gives you 0.33V per LED. So, you'd want the 1st LED to light at 1.33V, the 2nd at 1.66V, the 3rd at 2V, the 4th at 2.33V, and the 5th at 2.66V. A resistor ladder can be used to derive the reference voltages into the inverting inputs of 5 comparators; then feed the battery voltage directly into the non-inverting inputs of the comparators. Connect the LEDs to the comparator outputs with current-limiting resistors.

I'll leave it as an exercise to figure out what the resistor values in the ladder need to be. Partly because my algebra is a bit rusty after 30-odd years.

 

[duke37]

The LM3914 has ten comparators a reference voltage and is designed to drive leds, either as a dot or a bar.
As kpatz says, you will need a boost convertor and should consider how the capacitor voltage will hold up when you load it.

 

[Vinco]

thanks guys...any suggested boost regualtor to power the lm3914 chip?

 

[KrisBlueNZ]

Operation down to 1V is the special feature you need.

Linear Technology have several possibilities. Listed in order of increasing price:
http://www.linear.com/product/LT1610
http://www.linear.com/product/LT1613
http://www.linear.com/product/LT1307
http://www.linear.com/product/LTC3122
http://www.linear.com/product/LT1308A_B

Also check out TI and Maxim.