Help with LM3914 (5) bargraph chip

[Elephant]

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

 

[Anand Dhuru]

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

 

[Fred Bloggs]

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.