A level you can see
A bar graph is a number you read without reading. Ten segments is ten steps, which is too coarse for a meter and exactly right for a battery, a volume or a signal — and it is the trade you are making when you spend ten GPIO pins on one.
What the part is for
A number on a screen has to be read. A bar is taken in at a glance, from across the room, by somebody who is doing something else — which is why fuel gauges, volume controls and battery meters have looked like this for fifty years.
The cost is resolution. This part has ten segments, so it can show ten steps and nothing in between.
Half a step is five percent, and five percent is useless for a voltmeter and plenty for "how full is it". Decide which one you are building before you wire anything.
Bar or dot
The same ten segments do two different jobs depending on one line of code.
Bar mode lights every segment up to the level, so the display reads as a column filling. Dot mode lights one, so it reads as a needle moving. Dot mode draws a tenth of the current, which matters more than it sounds like it does — that number comes back in ten segments, one chip.
What it is not
It is not a display module. There is no driver chip in it, nothing to initialise, no library to install and no address to get wrong. It is ten LEDs in a plastic case, and every one of them needs its own wire and its own resistor.
That is the whole of the good news and the whole of the bad news, and the next page is about the twenty pins it takes to say it.
When it does not work
It is not, and that is the point. Ten segments can be wrong by half a step, so five percent. If the reader needs to know the number, print it; if they need to know whether it is going up, draw it. Most projects want both, on different parts of the screen.
Yes, by switching it on and off faster than the eye follows. That is PWM, and on an Arduino only six pins can do it in hardware, so a ten-segment bar cannot dim every segment that way without help. Dot mode and bar mode are the two things you can do with plain on and off.
Bar mode if the quantity is a level — a tank, a battery, a volume. Dot mode if it is a position or a reading, like a tuning needle, and whenever the display will sit lit for hours: one segment is a tenth of the current of ten.
Twenty pins, no chip, and the one thing about the part that is not printed on it.
Ten LEDs in one package →Edit this page — content/books/led-bar-graph/a-level-you-can-see.mdx
Questions about this product
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10-Segment LED Bar Graph Kit, 12 Bars in 6 Colours
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