Hi,
Having played around a bit more with 1 of these cascading into another I have the following problem which for the life of me I CANNOT FIX!!!
First of all...assume I have plugged these up as shown on the datasheet.
Second...assume I have plugged these up as shown on the datasheet.
The scenario is that I am feeding these a "signal" which varies between 1.25V and 0V and I want the two cascading LM3914's to act a a voltmeter as the signal goes from high to low and vice versa.
I am taking the reference voltage (1.25V) out of "chip 1" and feeding it back into Ref-Hi of chip 1. I am also passing it across 2 equal value resistors and then to earth to form a simple voltage divider. I am taking a feed from between the 2 resistors (0.625V) and sending it to Ref-Lo of chip 1 and Ref-Hi of chip 2 and am connecting Ref-Lo of chip 2 to earth.
The circuit appears to behave itself very well...ie the led's illuminate in accordance to the input voltage and track up and down the scale in a linear fashion.
HOWEVER....if the input signal is above Ref-Hi of the second LM3914 (0.625V) then LED No.10 of that chip (pin 10) is always illuminated.
SO...whenever the signal is above 0.625V and LM3914 No.1 is illuminating the "correct" LED I have LED No.10 on LM3914 No.2 illuninated as well.
If the signal falls below 0.625V then LM3914 No.1 stops illuminating any LEDs (as expected) and LM3914 No.2 behaves itself...ie the LED's track up and down as the signal goes between 0.625V and 0V and LED No. 10 goes out when it's suppose to.
So...assuming I have plugged these up as shown on the datasheet....
Has anyone come across this before?
Am I doing something silly?...ie, have you plugged this up accoring to the datasheet and found that it works fine???
Or...if you've got a simple circuit diagram of how you'd do this please feel free to post it!!!!!
Kind Regards,
TVS