I have 2 LM3914 chips which I'd like to connect together to power up 20 LEDs. I can do it with 1 chip for 10 LEDs according to the datasheet, but not with 2 chips.
Anyone here has had experice with this chip at all that could give me a hand please?
My input voltage is 5v.
An help is appreciated,
Regards,
M.
Now there's a "blast-from-the-past!" An LM3914 chip...
You need to read more of the datasheet because the LM3914
is cascadable. The datasheet even has a disagram for a 20-LED
circuit. If you need 0-5v input then you'll need to change the
resistors on the RefOut and/or RefAdj pins.
Also, if your signal is 0-5v (analog, not PWM!) then V+ and V-LED
will need to be 8v or so.
Yes there is a diagram with 20 LEDs, but I don't know what to do with the rest of the pins to be honest.
Anymore complete diagrams at all?
Appreciated,
M.
Go further down to page 15. Although that circuit is for 0-2.4v
you can make mod's, per the datasheet, a for 0-5v signal.
I've made this circuit but still doesn't work.
Anything I'm doing wrong?
Any help is appreciated.
M.
M.,
How are people suppose to tell you why a circuit isn't working if all
that you tell us is that it's not working? For all we know, the circuit
could be working perfectly and you don't recognize it as such.
Are you sure of your wiring and it actually matching the circuit
diagram you've given?
One thing is for certain, you're powering the circuit with 5v yet
you're expecting it to react to an imput signal of upto 5v..
All examples in the datasheet show a maximum input at least
1.2-1.5v below V+.
Not sure why you have 5v on pins (REFout & Rhi on the bottom 3419)
that's tied to ground (i.e. 0-volts normally). Certainly no 5-volts there
according to your diagram. And the original circuit (per page 8)
shows at least one resistor between those pins and ground.
Grounding the REFout puts zero volts across the resistor divider
network (in the chip itself) so there's no way any LEDs could ever
turn on. Since REFout is actually a voltage output from within the
chip, you may have damaged at least one of your 3419's by shorting
this output to ground. Again, all examples in the datasheet have at
least one resistor between this pin and ground.
How 'bout if you build the 20-LED circuit on page 15, for a signal
between 0->2.4v, and get it working before trying to modify it for
your own needs?? Start by building a circuit that's known to work
to understand some of the concepts then move on to modifications.
OK? 
Cheers mate.
I will try that and will let you know the outcome.
Regards,
M.
Also,
The pin 7 is connected to ground (-ve) after it's been connected to a resistor. Am I right?
M.
In what way does the circuit not work?
Well basically when I connect everything according to the circuit above, when I turn the potentiometer connected to the pin 5. None of the pins on IC 1 (top IC on diagram) get any signal so no LED gets lit, and only 11-18 pins on IC 2 (bottom IC on diagram) gets lit.
As our friend "Rusty in Texas" mentioned, the reason why it doesn't work is coz there is no resistor on pin 7???
Or maybe the way I have done it, according to the diagram I've put on the thread, is wrong!?
M.
So I tried the circuit exactly like the diagram on page 15, and all I get lit is the LEDs on pis 10 to 17 on second IC (bottom IC on the diagram). nothing turns on on first IC or the 1st or 18th pins of the 2nd IC.
What am I doing wrong?
M.
M.
Today I drove down to Dallas, TX and around to Garland (a suburb)
to pick up some LM3914's. You better check your wiring and
orientation of your chips and LEDs because I wired up the schematic
on page 15 (input: 0-2.4v, V+ of 5v) and it worked just perfectly. I am
using a 5K pot between ground and 5v to generate the input signal on
pin 5 (on both chips) and I left out the BAR/DOT switch and just
hardwired things for BAR mode.
BTW, what are you using for the input signal to both pin 5?
What voltage are you measuring on both chips' pin 5?
I'm also imagining that the LED's on the first chip and the first two
on the second chip (pins 1 & 18) are installed backwards because
these should be on if pins 10-17 on the second IC are lit since these
are indicating a full-scale (or higher) voltage.
-Rusty-
I now have it working mate. Thanks for all the help.
Matin.
What was the trouble?
Probably the connections. I disconnected everything, then started connecting everything again. And it worked.
Thanks alot.
M.
