LM3914

[Dennis Bell]

Make sure that the base voltage on your brightness control transistor does not
exceed about 5 volts when the lights are on. The typical base to emitter reverse
breakdown voltage is around 6 volts. If you exceed this voltage you will inject
current into pin 7 and raise the reference voltage when the lights are on.. A
resistor divider can be used on the base to limit the voltage.

Regards,
Dennis


BIGED2022 at aol.com wrote:

> I made an O2 sensor meter with LED display driver LM3914 for my truck and it's
> really neat.  I got the info from you guys, thanks.  I added a transistor to
> the LED brightness control section and connected it so the LEDs dim when I
> turn on my headlights.  This headlight dimming feature throws the 1volt
> calibration off about .1 volt when I turn on the headlights.  How come?  I
> have a 2.2k resistor and a 1k pot between pins 6 and 7 that I adjust to
> calibrate full scale to 1 volt. Pin 7 goes to ground thru a PNP transistor and
> a 680 ohm resistor on the emitter. The base of this transistor is connected to
> a wire that has 12v when headlights are on.
> One question on the O2 sensor.  How fast should the voltage swing rich/lean
> overall?   Mine swings rich to lean fairly steadily about every .5 to 1
> second,  seems slower than what I expected.
> Thanks
> Eddie Lord