I'm just wondering if I can make it smaller. I would need 8 x LM3915s.
It's still an option though.
I looked at making the 8 x 10 segment display with an MCU and after hitting a few dead ends, I came up with this:
![](http://i.imgur.com/clnRNRs.png)
Requires only 3 MCU pins. Allows up to 50mA per LED block, 5mA per LED.
My first attempt was with 5 LED drivers and a non-multiplexed display, which would be fine and take a lot of the burden off the MCU while it samples the ADC, however the peak current consumption could be as high as 160mA even if only 2mA per LED is used. The power supply for the whole project is 200mA and I'm already concerned about it, so unless I power the meter board separately, 160mA is too much.
My second attempt was to use two LED drivers to multiplex, but that was quickly aborted as all LED drivers are current sinks, not current sources.
My third attempt was with the 4067 multiplexer and that limited me to 25mA per 10 digit block, due to the 25mA per pin limit on the 4067. I did consider attaching each 10 segment to two pins, then realised that's blond as the multiplexer only has one active output.
So... adding a high side mosfet onto the multiplexer gets me the higher current for each 10 segment block.
I'm not sure it's correct of it will work.
It "should" be smaller. An 2xSSOP-24s + 1xQFP-32 + a couple of quad op amps/capacitors on the front end. That I would need with the LM3915s anyway. That should be fittable on a board not much larger than the LED bars, athough the bars are through hole which might lead to some interesting layout shenanigans.
Besides doing it with an MCU means I can do cooler things with the LEDs as well... and output two channels for strips of NeoPixel LEDs and drive the master levels into half meter LED strips up the back sides of my monitor.... might be cool. Stuff like that.