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I wanted to use a 12 LED bar graph with a LED bar graph driver but the the driver I know (LM3914) supports only 10 LEDs. Is there a similar driver IC with more out pins?

The purpose is to use the bar graph as a battery voltmeter. DIP package preferred.

Kokachi
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    Use a small micro... – Trevor_G Jan 09 '18 at 19:00
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    @Trevor Upped the comment because these days everyone needs to be familiar with embedded toolchains. But it does involve an embedded toolchain and that means the *project* now requires an installation of same in order to replicate the project elsewhere. It's a double-edged sword, I guess. It's dirt cheap and easy, takes up no added space, is flexible to future changes in concept, etc. But it all comes with a price, too. – jonk Jan 09 '18 at 20:34
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    Since this is for a battery voltmeter, is this meter being used to help you decide on the remaining charge of a battery of a certain chemistry? – jonk Jan 09 '18 at 20:36
  • @jonk I agree. but figured I'd suggest it before someone else did ;) – Trevor_G Jan 09 '18 at 21:16
  • I have used 3 LM3915 LED drivers to give me 90 dB of range on audio signals. This IC is cheap and still common on the markets. Just buy another one and read one of the many application guides for this IC so you can daisy-chain them. –  Jan 09 '18 at 23:17
  • Why the 'close' vote? That is getting picky. –  Jan 09 '18 at 23:22
  • @jonk yes this is going to measure a tubular 12v lead acid battery voltage. I will be using an tiny13a mcu to monitor the voltage and give audible warning if voltage is not back at proper levels each 24 hours. – Kokachi Jan 10 '18 at 03:52
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    @Kokachi Do you plan to "load" the battery while making measurements? Also, it seems to me a lot easier to use an MCU for this and since you actually are using one, why not have it (or something with enough pins) do the work here? Actually, I question the very idea of a 12-bar LED. It's either (1) too much information or else (2) too little information where it matters. For ex, a AA alkaline is pretty much dead at 1.2 V. It's pointless to show with LEDs that the voltage might be 0.9 V, right? I would want to rough % values. And this requires an MCU table, I think. Do they make a 12-LED bar? – jonk Jan 10 '18 at 05:09
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    @Kokachi I'd tend to imagine a circuit that provides a fixed loading on the battery without respect to the battery voltage (use PF5102 JFET probably) and that this provides the MCU with a resulting voltage to measure. That would be looked up in a table. Appropriate LED signalling then applied. Could even be a blinking LED with slow blink indicating very low, rising in rate until a solid ON means "fine." if you need more resolution, that's fine. But do you really need 12 LED bars? What does each one represent, then? – jonk Jan 10 '18 at 05:13
  • @jonk ok fine you have convinced me, I will use an arduino nano instead of 3914. Still wanted to know if there exists any such driver similar to 3914 with more pins just for curiosity. Yes they do make [12-LED bars](http://electroniccomponentstore.co.uk/wp-content/uploads/2017/03/S55-1620P01WL.jpg), use for stereo amps and stuff. – Kokachi Jan 10 '18 at 08:02
  • @jonk yes the battery will be connected to both load and a charger (actually it's a home inverter setup) while measuring the voltage. Each bar represents approximately 0.18 volts. I could live with just 10 bars resolution but then the extra 2 bars would be wasted so I thought I'd make use of them too. – Kokachi Jan 10 '18 at 08:07
  • @Kokachi If you didn't want to completely waste the extra two bars you could tie them together, or do the bottom two bars as 2 bar increments, so tie LED driver pin 1 to LEDs 1&2, and LED driver pin 2 to LEDs 3&4 – Ticktok Jan 10 '18 at 16:49
  • @Kokachi although, now that I see you're using a microcontroller, I would definitely suggest just driving the LEDs with that. Rather than using a larger mcu, if you can still get 1 spare pin on the ATtiny13A, then you can use a 12 bit shift register such as the TLC6C5912-Q1 and all 12 LEDs with finer controller over when/what is displayed. – Ticktok Jan 10 '18 at 16:53
  • err, 3 pins need a clock pin as well to clock in the serial data and an enable pin. – Ticktok Jan 10 '18 at 17:08

1 Answers1

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I wasn't able to find a 12+ driver with a quick google search, but a fairly easy(although larger) implementation would be to just use two LM3914's.

There's an example in this spark fun tutorial

Just hook up LEDs 1-10 to the first one, then feed the RLO output to the RHE of the next driver and connect the last 2 LEDs to it.

Edit: Information added as per my comment above.

Since you're already using a microcontroller, just drive the LEDs with that. Rather than using a larger mcu, if you can still get 3 spare pins on the ATtiny13A, then you can use a 12 bit shift register such as the TLC6C5912-Q1 and all 12 LEDs with finer controller over when/what is displayed.

Here's a schematic because I have entirely too little to do at work right now. Based upon This instructable although they use the ATtiny85. I'm not sure what external circuitry you're using to measure/load the battery, as after a little googling, the ATtiny13a doesn't have an internal reference.

schematic

simulate this circuit – Schematic created using CircuitLab

Ticktok
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  • I saw such a thing in a youtube video and the reason I don't like it is because the extra 3914 wastes a lot of space. However if there was an LED graph driver with just 6 or 7 pins then I would gladly use 2 of them. – Kokachi Jan 10 '18 at 03:47
  • Great, a shift register sounds neat. Must find a 12 bit one, everything sold here are only 8 bit. Might use a TL431 for reference, or could use tiny85 instead. The circuit you posted why use caps for the regulator since power is coming from a battery? – Kokachi Jan 11 '18 at 06:10
  • The caps are smoothing caps, also known as a voltage well. As the micrcontroller/shift register are switching, they're going to draw down the voltage. Say you turned all 12 LEDS at once, that would be a sudden draw on the the regulator, which would in turn draw from the battery. This creates what's called a depletion wave which and creates noise and if severe enough can cause brown outs(if you were running that close to minimum voltage). So the capacitors are there as a well to store some voltage that can maintain the level as things are turned off and on. – Ticktok Jan 11 '18 at 07:45
  • Also, if you connect anything else to the battery and when that turns on it draws it down, that can drop below the regulators threshold. – Ticktok Jan 11 '18 at 07:45
  • Thanks, I never thought power from a battery would have noise. – Kokachi Jan 12 '18 at 05:13