In this video, we will be learning how to use LM3914 which is a Dot or Bar Display Driver. This Dot or Bar Display Driver can be used as a voltage level indicator across 10 LEDs. Maximum of 25V can be used with this chip. Maximum ratings of this chip can be found in the datasheets which are highly ubiquitous.
Below figure, shows how the circuit can be connected:
Pin 1, 10 - 18 are connected to the cathode of 10 LEDs.
Pin 2 and 4 are connected to ground.
Pin 3 is connected to Pin 9. Pin 6 is connected to Pin 7.
Pin 5 is the Voltage Signal Pin which will determine how many LEDs will light up at once or which one of those 10 LEDs will light up, depending on the mode selected at Pin 9
Pin 9 is Mode Pin. When HIGH, it will be in BAR Display mode and when low it will be Dot Display mode.
Pin 8 is connected to the juncture of R1 and R2.
Refer Figure below for breadboard connection:
Determining the value of R1 and R2 is very important for the chip to work as we want.
Having the correct resistance value in R1 and R2, will help with:
Ensuring safe current amount to all LEDs
Ensuring correct number of LEDs light up according to Signal Voltage Value in PIN5
In determining how much current is routed to the LEDs, we would need to use the below formula:
I = 12.5/R1
Which is found in the datasheet. We are assuming, a safe amount of current for each LEDs which would be 10mA. Inserting this value into the equation, gives us the R1 value
R1=12.5/10mA=1.25kOhm
Next, we can decide what our R2 value is
Ref Voltage=1.25(1+R1/R2)
Ref Voltage is basically the maximum voltage that we expect in our usage. For an example, if your batteries full charge will be 8V, then our Ref Voltage will be 8V as well. In other words, all 10 LEDs will light up when 8V is detected at Pin 5.
Inserting the values of Ref Voltage=8V and R1 =1.25kOhm into the equation
8V=1.25(1+1.25kOhm/R2)
R2=6.75kOhm
The nearest resistor that I have is 6.9kOhm.
I have a created the below table to show the relationship between Vcc or Ref Voltage between the number of LEDs that will light up according to Signal Voltage(PIN5).
This characteristic of LM3914 makes the chip highly versatile in acting as a battery/voltage level indicator making it a very useful feature to be incorporated in our electronic projects.
For live view of this project and more explanations, check out my YouTube video
Thank You and Good Luck Trying!!