Help with LM3914 (5) bargraph chip

E

Elephant

Guest
I hope this isn't too long. I'm unable to supply any graphics as to
my hook up.

Pins 2,4 & 8 go to negative side of 9vdc supply.
Pins 3 & 9 go to the positive side

Pins 6 & 7 are connected together, then to ground thru a 4.7K resistor.

Of course, 10 LED's are hooked to pins 1 thru 18

Without anything hooked to pin 5, and power is applied, all 10 LED's
light up.

Can anyone tell me what I'm hooking up wrong? I of course went
through the entire circuit checking for shorts, can't find any.
Tried 3 or 4 chips and they all do the same (thinking I had a bad chip).

A final note, the completed project will be hooked to the output of
an AM transistor radio to detect lightning strikes.

Any input would be very much appreciated.

Doug
 
Hi,

Try putting a capacitor (0.47 uF) across the input and ground between
pin 5 and 2/4/8.

Your input pin left open and floating can catch a lot of noise,
driving the extremely sensitive input stage to saturation.

And, do let me know if this works; I'm very curious!

Regards,

Anand Dhuru


Elephant <elephant@the-zoo.com> wrote in message news:<4064CDBF.6737@the-zoo.com>...
I hope this isn't too long. I'm unable to supply any graphics as to
my hook up.

Pins 2,4 & 8 go to negative side of 9vdc supply.
Pins 3 & 9 go to the positive side

Pins 6 & 7 are connected together, then to ground thru a 4.7K resistor.

Of course, 10 LED's are hooked to pins 1 thru 18

Without anything hooked to pin 5, and power is applied, all 10 LED's
light up.

Can anyone tell me what I'm hooking up wrong? I of course went
through the entire circuit checking for shorts, can't find any.
Tried 3 or 4 chips and they all do the same (thinking I had a bad chip).

A final note, the completed project will be hooked to the output of
an AM transistor radio to detect lightning strikes.

Any input would be very much appreciated.

Doug
 
Elephant wrote:
I hope this isn't too long. I'm unable to supply any graphics as to
my hook up.

Pins 2,4 & 8 go to negative side of 9vdc supply.
Pins 3 & 9 go to the positive side

Pins 6 & 7 are connected together, then to ground thru a 4.7K resistor.

Of course, 10 LED's are hooked to pins 1 thru 18

Without anything hooked to pin 5, and power is applied, all 10 LED's
light up.

Can anyone tell me what I'm hooking up wrong? I of course went
through the entire circuit checking for shorts, can't find any.
Tried 3 or 4 chips and they all do the same (thinking I had a bad chip).
Pin 5 requires a DC path to GND for the bias current, add a 1M resistor
from pin 5 to GND.
 

Welcome to EDABoard.com

Sponsor

Back
Top