Strange quick with the LM3914-N1

[Colin Dawson]

I've built a bar graph circuit on a bread board. The circuit diagram is
available at

http://www.cjdawson76.btinternet.co.uk/circuits/potdrivenbar.jpg

Everything seems to work OK, until set the 1k Pot (Labelled VR2) to 100%.
My circuit modelling software says that this should light the LED labelled
D11 (it's on pin 10 on the chip). However, on my breadboard version the
last LED, only gets enough power to come on, but not to full power like the
others.

How can I sort this out?

Regards

Colin Dawson.
www.cjdawson.com

 

[CFoley1064]

Subject: Strange quick with the LM3914-N1
From: "Colin Dawson" news@cjdawson.com
Date: 3/27/2004 12:09 PM Central Standard Time
Message-id: <c44g1e$f8n$1@hercules.btinternet.com

I've built a bar graph circuit on a bread board. The circuit diagram is
available at

http://www.cjdawson76.btinternet.co.uk/circuits/potdrivenbar.jpg

Everything seems to work OK, until set the 1k Pot (Labelled VR2) to 100%.
My circuit modelling software says that this should light the LED labelled
D11 (it's on pin 10 on the chip). However, on my breadboard version the
last LED, only gets enough power to come on, but not to full power like the
others.

How can I sort this out?

Regards

Colin Dawson.
www.cjdawson.com

Another thing you might want to look at is the minimum resistance of your pot.
Take it out of circuit and measure it with an ohmmeter.

Good luck
Chris

 

[cpemma]

Colin Dawson wrote:

I've built a bar graph circuit on a bread board. The circuit diagram
is available at

http://www.cjdawson76.btinternet.co.uk/circuits/potdrivenbar.jpg

Everything seems to work OK, until set the 1k Pot (Labelled VR2) to
100%. My circuit modelling software says that this should light the
LED labelled D11 (it's on pin 10 on the chip). However, on my
breadboard version the last LED, only gets enough power to come on,
but not to full power like the others.

How can I sort this out?

Try increasing R14, this sets the led current to 12.5/R14, 8.3mA with the

existing 1k5. A 2k2 or 2k7 will reduce the load, a bit near the border in
bar mode.
--
Home Rule for Yorkshire

 

[Colin Dawson]

"cpemma" <me@privacy.net> wrote in message
news:c47o9d$2d9vp6$1@ID-109861.news.uni-berlin.de...

Colin Dawson wrote:
I've built a bar graph circuit on a bread board. The circuit diagram
is available at

http://www.cjdawson76.btinternet.co.uk/circuits/potdrivenbar.jpg

Everything seems to work OK, until set the 1k Pot (Labelled VR2) to
100%. My circuit modelling software says that this should light the
LED labelled D11 (it's on pin 10 on the chip). However, on my
breadboard version the last LED, only gets enough power to come on,
but not to full power like the others.

How can I sort this out?

Try increasing R14, this sets the led current to 12.5/R14, 8.3mA with the
existing 1k5. A 2k2 or 2k7 will reduce the load, a bit near the border in
bar mode.
--
Home Rule for Yorkshire

I've re-done the circuit a coupe of times, as a result of the help that I'm
getting on sci.electronics.design.
The problem with increasing R14 is that whilst the current is slowed, the
LED's get dimmer. There's not
enough power to run the LED's.

Regards

Col.

 

[Colin Dawson]

"Colin Dawson" <news@cjdawson.com> wrote in message
news:c48n47$3ht$1@hercules.btinternet.com...

"cpemma" <me@privacy.net> wrote in message
news:c47o9d$2d9vp6$1@ID-109861.news.uni-berlin.de...
Colin Dawson wrote:
I've built a bar graph circuit on a bread board. The circuit diagram
is available at

http://www.cjdawson76.btinternet.co.uk/circuits/potdrivenbar.jpg

Everything seems to work OK, until set the 1k Pot (Labelled VR2) to
100%. My circuit modelling software says that this should light the
LED labelled D11 (it's on pin 10 on the chip). However, on my
breadboard version the last LED, only gets enough power to come on,
but not to full power like the others.

How can I sort this out?

Try increasing R14, this sets the led current to 12.5/R14, 8.3mA with
the
existing 1k5. A 2k2 or 2k7 will reduce the load, a bit near the border
in
bar mode.
--
Home Rule for Yorkshire



I've re-done the circuit a coupe of times, as a result of the help that
I'm
getting on sci.electronics.design.
The problem with increasing R14 is that whilst the current is slowed, the
LED's get dimmer. There's not
enough power to run the LED's.

Regards

Col.

Yay, it's working, and fortunatly, I only blew two chips in the way there


WOOHOO Thanks to all that helped me with this. Next stop battery monitor
version of the circuit (once I've made this one into a PCB version )

Regards

Colin.

 

[cpemma]

Colin Dawson wrote:

"Colin Dawson" <news@cjdawson.com> wrote in message
news:c48n47$3ht$1@hercules.btinternet.com...

"cpemma" <me@privacy.net> wrote in message
news:c47o9d$2d9vp6$1@ID-109861.news.uni-berlin.de...
Colin Dawson wrote:
I've built a bar graph circuit on a bread board. The circuit
diagram is available at

http://www.cjdawson76.btinternet.co.uk/circuits/potdrivenbar.jpg

Everything seems to work OK, until set the 1k Pot (Labelled VR2) to
100%. My circuit modelling software says that this should light the
LED labelled D11 (it's on pin 10 on the chip). However, on my
breadboard version the last LED, only gets enough power to come on,
but not to full power like the others.

How can I sort this out?

Try increasing R14, this sets the led current to 12.5/R14, 8.3mA
with the existing 1k5. A 2k2 or 2k7 will reduce the load, a bit
near the border in bar mode.
--
Home Rule for Yorkshire



I've re-done the circuit a coupe of times, as a result of the help
that I'm getting on sci.electronics.design.
The problem with increasing R14 is that whilst the current is
slowed, the LED's get dimmer. There's not
enough power to run the LED's.

Regards

Col.



Yay, it's working, and fortunatly, I only blew two chips in the way
there

Glad it's working, but why are you using resistors in series with the leds?

The 3914 sets a fixed (by R14) led current at each comparator so the extra
current limiting isn't necessary AFAICS, and may be the root cause of the
uneven illumination.

Have a look at the Block Diagram's basic circuit in the datasheet.
--
Home Rule for Yorkshire