from the datasheets for lm3914 it looks like the lowest full scale i can get is 0-1.2v. can it be made to 0.5v or 0.2v full scale?
also, i am confused slightly about how Ref(out) and Ref(adj) work when they are tied to each other via voltage divider (shown on the 1st page of LM3914 datasheet at National's website http://www.national.com/mpf/LM/LM3914.html). i see that the 2 resistors add up to 5k, and the scale is 0-5v. does the addition of the 2 resistors equal the upper limit in voltage? but i dont quite get why Ref(adj) is connected into the voltage divider. can anyone explain how these work.
what i am wanting to do is to be able to change the scale using dip switch (hence changing some resistor values without changing my set LED currrent). as example, i want to scale it 0-2.5v full scale, then with a dip switch flip the scale becomes 0-5v, etc. can this be done? would i just change R2 from 3.83k to 8.79k (10k - 1.21k = 8.79k)? but according to the block diagram Ref(out) to ground load determines LED current, so if i'm changing R2 then i am also changing LED current at the same time. i want to keep LED current fixed no matter what scale i choose, etc.
from the datasheets for lm3914 it looks like the lowest full scale i can get is 0-1.2v. can it be made to 0.5v or 0.2v full scale? as example, i am monitoring current of a inductor via a 0.1 ohm resistor in series with the inductor. my known currents (depending on inductor used) is 2amp and 10amp. with 2amps i'm only gonna see about 200mV across the resistor. do i need a diff op amp to boost this up some for lm3914? but as you can see from the current ranges i want to be able to adjust the LM3914's scale by a factor of 5 (using dip switch, etc)
any ideas?
thanks
also, i am confused slightly about how Ref(out) and Ref(adj) work when they are tied to each other via voltage divider (shown on the 1st page of LM3914 datasheet at National's website http://www.national.com/mpf/LM/LM3914.html). i see that the 2 resistors add up to 5k, and the scale is 0-5v. does the addition of the 2 resistors equal the upper limit in voltage? but i dont quite get why Ref(adj) is connected into the voltage divider. can anyone explain how these work.
what i am wanting to do is to be able to change the scale using dip switch (hence changing some resistor values without changing my set LED currrent). as example, i want to scale it 0-2.5v full scale, then with a dip switch flip the scale becomes 0-5v, etc. can this be done? would i just change R2 from 3.83k to 8.79k (10k - 1.21k = 8.79k)? but according to the block diagram Ref(out) to ground load determines LED current, so if i'm changing R2 then i am also changing LED current at the same time. i want to keep LED current fixed no matter what scale i choose, etc.
from the datasheets for lm3914 it looks like the lowest full scale i can get is 0-1.2v. can it be made to 0.5v or 0.2v full scale? as example, i am monitoring current of a inductor via a 0.1 ohm resistor in series with the inductor. my known currents (depending on inductor used) is 2amp and 10amp. with 2amps i'm only gonna see about 200mV across the resistor. do i need a diff op amp to boost this up some for lm3914? but as you can see from the current ranges i want to be able to adjust the LM3914's scale by a factor of 5 (using dip switch, etc)
any ideas?
thanks