LM3914 external refrence?

[Llamarama]

Hello everyone, I'm trying to get a 20 segment driver by chaining a pair of LM3914s as per the datasheet, but i'm having trouble with the voltage reference pins. Is there any way I can manually set a high reference and a low reference (say with a pair of 1k multiturn potentiometers) whilst sticking in a fixed resistor to set the led current/brightness?

I don't know what values of inputs i'll be using yet, but more than likely between 0 and 5v. Also, would it be ok to run this circuit from 9 or 10v? In many of the circuits i've seen online, the supply voltage is at least twice the input voltage.

Any pointers would be greatly appreciated. Many thanks, Mike.

 

[alec_t]

Is there any way I can manually set a high reference and a low reference (say with a pair of 1k multiturn potentiometers) whilst sticking in a fixed resistor to set the led current/brightness?

Yes, you can do that. Connect Rhi and Rlo only to your respective refs, connect pin 8 to ground, connect the current-programming resistor between pins 7 and 8. Ok to run from a supply up to 15V.

 

[Llamarama]

Excellent, thank you

 

[crutschow]

Just note that the LM3914 power dissipation goes up with the supply voltage and the LED current, especially in the Bar mode.

 

[Llamarama]

Sorry to be a burden once again, I've been breadboarding layouts all night with little success. I can get a 10 segment version to work fine, but the 20 segment version doesn't work past 9 segments.

Once the 1th segment lights, it sticks and no further LEDs light up, this is when I feed it 4.5v.

I have (hopefully) attatched a schematic showing the circuit I'm using, does this look ok?

 

[4pyros]

No thats not right. Try this one;

 

[Llamarama]

Breadboarding as we speak, thank you

 

[Llamarama]

Right, it works fine for bar mode, however when connecting pin 9 of lm3914 1 to pin 1 of lm3913 2, and pin 9 of lm3914 2 to either pin 11 or completely disconnected as is mentioned in the datasheet, I get led 10 lit as soon as the lower scale in exceeded and it stays on. Any ideas as to why this is happening?

 

[4pyros]

Pin 9 of both LM3914"s needs to go to power for bar mode.

 

[eTech]

Here you go...

one shows circuit
one shows DOT graph
one shows BAR graph

eT