Vref calc for Casaded LM3914's

[eTech]

Hi

Working with LM3914s...

So...I understand how to calculate the Vref resistor values for a single LM3914.

But what is the procedure for calculating the Vref resistor values for three cascaded LM3914s?

For example, If I want to monitor a 5v signal using 3 LM3914s, I know that each LED will represent a 0.166v increase in signal level. So, assuming a 5v input signal and 10ma for each LED, how would each of the Vref resistor values be calculated for each of the three LM3914s?

eT

 

[cowboybob]

Is this what you mean? This is from the datasheet, page 16, of this site:

https://pdf1.alldatasheet.com/datasheet-pdf/view/8898/NSC/LM3914.html

 

[eTech]

Oh..ok...
Guess I missed that..

So..is that diagram implying a signal input range of 0-3v?

thanks

 

[dr pepper]

You can daisy chain the resistor strings in the '3914's and just use one as the reference, the top one, all the others just select the reference resistor to set the led current.

 

[cowboybob]

...all the others just select the reference resistor to set the led current.

and the voltage range within which each LM3914 will respond.

...So..is that diagram implying a signal input range of 0-3v?...

For the circuit provided, bumping the input signal to 5VDC shouldn't have a significant effect, other than slightly brighter LEDs. The adjustment range of R2 should accommdate the increase.

If it were me (and, of course, it's not) I'd use 510 ohms for R1, 3, 4 and 5 and the closest to R2's value as you can get and see if the '3915s respond adequately and the LEDs are bright enough for you.