Category: General Author: Thomas Comments: Tags: Build Your OwnElectronic Engineering

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Loochi 0.3 and 0.4

On august 24th, we announced that we were working on a new version of our lamp. We have updated the github regularly but had not posted any more technical news so here goes.

I have just renamed the hardware project to loochi-hardware and updated the README to describe our two newest boards: Loochi v0.3 and v0.4.

I am copying/pasting the description here. Be sure to check it out!

Loochi v0.3

Second complete prototype designed and built by us.

There is only one board with the LED soldered directly on the board. The PCB is intended to be an aluminium core PCB. For prototypes we have used traditional FR4 boards (from the awesome oshpark.com). In any case you absolutely need a pretty big heatsink on the other side of the board.

This board design is a major rework over the previous version. The main goal was to reduce manufacturing cost so that more people could enjoy Loochi. Another major design decision was to drop Wifi. We could write a lot about that but the biggest arguments were: (1) Wifi seriously increases the costs of the solution and (2) the efforts required by the user to set-up a Wifi lamp are important.

Main characteristics:

  • One ATTiny 861A is used to control the current going through the LED and adjust the brightness
  • One BLE112 module from Bluegiga is used for Bluetooth Low Energy communication with the app, it acts as an SPI Master to the Attiny
  • There is no more dedicated chip for the LED PWM (to reduce costs)
  • Ledengin 10W RGGB Led soldered directly on the PCB
  • Funny fact: the board radius is 3.1415925 cm

You will find more information on how this board works in the source code of the AVR. Several versions are provided (with graduating levels of complexity).

We also plan to do a video to explain how it works. If you are interested, let us know and it will probably be done quicker!

Known problems on the board layout

There are a few known problems on this PCB:

  • The LED footprint is wrong: the first green LED is backwards (stupid mistake when linking pads and signals)
  • The schematic uses the RESET pin of the uController but we decided later on to change that, the mapping used in the software is BSENSE connected to PB5 and BPWM connected to PB4 (which means the Blue PWM output is inverted but allows us to keep the RESET pin free)
  • The BLE112 module is very sensitive to the quality of the power supply, add an RC filter on its VCC
  • Remove Q4 and short its source and drain (otherwise you will get a shortcut) - Warning: this removes the reverse voltage protection

If you want to make your own, we suggest that you fix those before getting the board manufactured or wait for a new design from us that would not have those problems. Another option is always to cut some traces and put some small wires. This is what we have done.

Loochi v0.4

Third prototype.

This one is very similar to 0.3 but instead of a Bluegiga BLE112 module, we use an Aircable module with its generic firmware (so it does not need any programming). This module is not yet publicly available but will be very soon. Until then, you can contact us if you would like to get some.

In this design, we have also removed the npn/pnp transistors that were used to drive the mosfet. We wanted to compare the performance with and without them.

The communication protocol is labeled as I2C between the BLE module and the attiny but you can also do SPI. We have not really decided which one we will stick to.

Known problems and limitations

This board was designed before we had time to assemble the 0.3 so the same problem applies on the LED pads, and connections.

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