RPUlux - six constant current LED drivers with PWM from 328p

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Board with ATmega328p and six AL8805 constant current drivers and headers for my multi-drop serial Shields

This programmable ATmega328p based board has headers for an [RPUpi] or [RPUadpt] mezzanine shield. The program can use the ADC to monitor the input current with a high side current sense (ZXCT1087) on channel six, and the input voltage with a voltage divider on channel seven. Six AL8805 based constant current sources provide 330mA each for LED strings. The current controllers are connected to PWM pins (OC0A, OC0B, OC1A, OC1B, OC2A, OC2B) and may be modulated at up to 500Hz by program control.


See the [RPUlux] on Github for more information.


  • Evaluation ^2 with Managed Serial Bus Shields

    ronald.sutherland04/09/2018 at 07:56 0 comments


    RPUpi moved to the new RPUlux^2 and put a RPUadpt^5 on the PUlux^1.

    The Pi Zero has a WiFi dongle so I can SSH into it remotely. The RPUbus goes over the ubiquitous CAT5 cable wired for ethernet (not the crossover variant).

    Headless computers are a paradigm shift, I worry about how I will fix it if something goes wrong, but after switching from Raspbian Jessie to Stretch by way of a clean install I guess in the worst case it is easy enough to sanitize.


    Notes firmware could be written to shutdown the battery backed Pi if the power is out for an extended period. The Wifi and network services (DHCP,DNS Host Mapping) also need to be battery backed for a laptop to be able to access them.

  • AVR weak pull-up and AL8805 analog CTRL

    ronald.sutherland03/28/2018 at 20:11 0 comments

    I was having problems with my SelfTest where I was only seeing about half the expected current from an AL8805.

    An 8.45k Ohm pull-down was used to turn off the LED's during boot loading and when the AVR is in RESET. Form the AL8805 CTRL perspective the pull-down sums a divided amount from the AVR 5V through a 35k Ohm (weak pull-up mode) and from the 2.5V reference on AL8805 through 50k Ohm.


    With a 3.74k Ohm pull-down and a weak pull-up from the AVR the switch mode converter runs with an analog setting in the range 50mA to 150mA (approximate).


    When the AVR pin is in the push-pull mode and set HIGH the constant current converter provides the expected amount of current. The weak pull-up mode from the AVR set an analog voltage on the AL8805 CTRL pin that allows it to run at a reduced current without any audible switching noise (e.g. the 500Hz).

  • Continuous Integration (CI) with AVR

    ronald.sutherland03/09/2018 at 23:27 0 comments

    I am trying out Travis CI with the firmware for this board, having never used CI before I was fairly clueless, and mostly still am. From what I can see, a push to Github notifies Travis which starts a fresh instance of Ubuntu 14.04 (that seems a little old to me) then pulls a clone of the repo and looks at the config file ".travis.yml" inside to tell it what to do. Basically, I followed an [example] I found.


    Another example I found made me think this was going to be too difficult, but it did clue me in about how to use a matrix with the Travis system so I added that to the setup I could follow.

    This is what it looks like

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