I need help understanding this circuit for one of my assignments. This circuit is supposed to be a battery level indicator for 12V batteries, but I am unclear of how the resistor values were selected for the 18k, 56k and 10k potentiometer. Are there any formulas that could help me understand this better? I'm attaching a picture of the circuit and the datasheet link for the chip. Thank you
The datasheet explains what is happening:
A constant current (Adjustable) creates a reference voltage. The input voltage is compared with the reference... full voltage input, all LEDs. As the input drops lower, LEDs extinguish.
Those form a voltage divider that is used to supply a demonstration signal input to the device.
The 10K pot will set the signal voltage between 0 and 10/(10 + 56) or ~15 percent of the + voltage powering the circuit.
Like ~1.8 volts at the max if you were using a 12 volt supply.
The LM3914 and LM3915 are clever devices and a thorough reading of the datasheet will reveal a wealth of application ideas.
a7
I do not see any attempt to solve the problem, is this a student project? I would suggest start by building the unit shown on the data sheet and work with that until you understand it. Then go into the schematic you have shown. It is nothing more than a fancy voltmeter.
Why is your datasheet almost empty?
It's not, any problems with accessing it? I'm mostly interested in page 8 since it shows the layout of LM3914
R2 (together with the 1k's inside) determines at what voltage the first led starts to burn.
56k and 10 k at 48% will divide approx. 12V to the ref voltage. Here you can set the voltage at which all led's should burn.
I have merged your cross-posts @perishben.
Cross-posting is against the Arduino forum rules. The reason is that duplicate posts can waste the time of the people trying to help. Someone might spend a lot of time investigating and writing a detailed answer on one topic, without knowing that someone else already did the same in the other topic.
Repeated cross-posting can result in a suspension from the forum.
In the future, please only create one topic for each distinct subject matter. This is basic forum etiquette, as explained in the "How to get the best out of this forum" guide. It contains a lot of other useful information. Please read it.
Thanks in advance for your cooperation.
So what do we see in the layout on page 8? I see a tall resistor string of 1.0 Kohm resistors. Looks like a voltage divider to me. Ground on the bottom and Rhi on the top. Each output leg of the divider goes to a (+) non-inverting input of a comparator. The (-) inverting input of each comparator. Your Signal In comes in through a unity gain buffer (the op-amp in the drawing and there is a polarity protection diode to ground. The buffer out runs to all of the comparator inverting inputs. So what happens? Each comparator has a fixed reference voltage on the non-inverting input based on the divider string. When the voltage into each comparator exceeds the Vref from the divider the comparator out goes logic low illuminating the LED on that comparator. Start with a read on how a comparator works.
Ron
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