Electronic – How to efficiently trigger QC and convert it to constant 5V and a peak of 5A

5vchargingdcstep-downusb

Introduction

For a university project I started working on RGB LED Shutter glasses, which are based on the idea of a kickstarter by Macetech. However, these glasses miss some features I was looking for and therefore seemed a good idea to improve upon. Also, they are pretty expensive and most components were given by my university so I was very glad my idea was chosen for the project. That said, our project goal was pretty simple: reverse engineer these glasses and make them react to sound.

However, during the project I stumbled on some pretty cool other use cases for these glasses and therefore decided to develop it further in my free time. However, our prototype is very rough. The LED's are on a pcb which is taped on some 3d glasses and a four threaded wire is connecting the LED pcb to the microcontroller. Not quite nice looking…

Since I want to use these glasses for myself (and wearing them at festivals), I want to make them look more professional. So I'm planning to create a 3D design which is bulkier than normal glasses but doesn't look stupidly big. This means all my electronics (except power) must fit in a small case in the glasses itself. For that, the legs of the glasses seem the best idea, especially if only one leg is used. This volume is approx. 4x6x1 cm.

The electrical components for in the glasses' legs are:

Wemos D1 mini pro
3 buttons and a pull down resistor for each button
Small microphone (max4465)
Connector for power (located at the end of the legs of the glasses, so not in the said dimensions)
Power delivery circuit (constant 5V, max 5A)

The Problem

Therefore I'm looking for a way to get quite a lot of power to these glasses. The WS2812B I'm using has a max current of 60mA per LED, of which I have 72 which accounts for 4.32A. Normally these leds function on 5V, but they also seem to do fine on a bit less (li-ion voltage of 3.7-4.2V). So in the worst case they can suck 21.6W. Later on, I'm also planning on increasing to more leds while still maintaining the same surface. So for that I will be using the sk6812 mini, which I'm able to squeeze 100 leds on a new verion of the pcb. This will account for 50mA per led, which is at peak 25W.

Since I like to reuse the whole power design, I'm looking for a way to get constant 5V, max 5A. The way which seemed the most ideal to me was using a powerbank which has quick charge. To trigger this I could use a qc trigger board (as suggested here) and then step the voltage down to the desired 5V 5A. However these two boards are pretty large and certainly won't fit in my glasses.

I also found it's pretty simple to trigger qc, but since I don't want to waste power pulling a constant 12V doesn't seem like a good idea.

Last thing was that I saw a usb c qc trigger board on aliexpress, but these boards are very expensive.

The question

So I'm interested, how I can efficiently pull power from a QC power bank and step it down to a constant 5V and a max 5A, while maintaining a small size?

TLDR

I'm looking for a small circuit which can trigger QC and convert it to a constant 5V and a peak of 5A. How can I achieve this? Also, other options are welcome as well.

Bonus info

Earlier on, I said that I wanted more features from my LED glasses and will tell here more about that.

My glasses are currently able to display approx. 30 cool presets, but I have quite a lot of others in the making. Some of these presets have quite a lot of customizability, like setting a color (or on some a palette), showing different forms or reacting to sound or not. I also can show text and adress a certain letter with a color. And last but not least, it sort of works with ARTNET (recieves data, atm doesn't tell it's an ARTNET device). Also, I like to make an app which can control a certain preset and configure all the different options of it.

Best Answer

The way I solved this in the original macetech RGB Shades:

Full power is too much, cap it in software

It turns out that running 12-15 watts of LEDs on your face is too much. I have customers asking me frequently for reduced brightness levels, even though the stock RGB Shades firmware ships with brightness capped to 1/3rd of the maximum brightness (with 5 adjustable levels reducing the cap to less than 1/10th the possible brightness).

If you're in a darkened room, even 1/10th brightness over 68x3 = 204 LEDs can be quite blinding. Running them at maximum brightness also can cause the panel to get hot to the touch and physically uncomfortable.

By shipping the shades with brightness capped in software, they run fine from a normal pocket-sized USB power bank. Customers still want it dimmer, so there is no need for a high-current supply. Designing for maximum LED output is a distraction in this application, you will find yourself looking for ways to reduce the current, not increase it.

Filter analog supplies to reduce power rail interference

With normal USB cables, we saw pretty significant power rail bounce depending on the LED pattern. This interfered with a later MSGEQ7-based microphone audio sensor. The solution was to use a small inductor and resistor to filter the power rail, and to have custom power-only USB cables made that both had thicker power conductors than normal USB cables, and were thinner and more flexible than normal USB cables since they only had two conductors.

Much of the audio-specific design process is captured here, if you need additional information (and OSHW design files): http://www.macetech.com/blog/node/144

Related Solutions

Electronic – How to Efficiently Decode Non-Standard Serial Signal

Another answer: Stop using interrupts.

People jump to use interrupts too easily. Personally, I rarely use them because they actually waste a lot of time, as you are discovering.

It's often possible to write a main loop which polls everything so rapidly that's it's latency is within spec, and very little time is wasted.

loop
{
    if (serial_bit_ready)
    {
        // shift serial bit into a byte
    }

    if (serial_byte_ready)
    {
        // decode serial data
    }

    if (enough_serial_bytes_available)
    {
        // more decoding
    }        

    if (usb_queue_not_empty)
    {
        // handle USB data
    }        
}

There might be some things in the loop which happen far more often than others. Perhaps the incoming bits for example, in which case, add more of those tests, so that more of the processor is dedicated to that task.

loop
{
    if (serial_bit_ready)
    {
        // shift serial bit into a byte
    }

    if (serial_byte_ready)
    {
        // decode serial data
    }

    if (serial_bit_ready)
    {
        // shift serial bit into a byte
    }

    if (enough_serial_bytes_available)
    {
        // more decoding
    }        

    if (serial_bit_ready)
    {
        // shift serial bit into a byte
    }

    if (usb_queue_not_empty)
    {
        // handle USB data
    }        
}

There might be some events for which the latency of this approach is too high. For example, you might need a very accurately timed event. In which case, have that event on interrupt, and have everything else in the loop.

Electronic – Charging 10 AA nimh batteries in series

Your best bet is to locate a NiMH charge controller IC and build your charger using the recommended circuit for that IC.

Charging batteries is a tricky process if you intend to do it without destroying the cells. It is even trickier if you have a large number of cells in series.

Figuring out how to do it right is a job for a professional engineer, and finding all of the needed conditions has been the subject of many a research project.

The ICs will have all of this knowledge and know how "baked in." If you just need to build a charger, this is the easiest way.

If you are building the charger to learn how to make such a controller, you will need to do a lot of reading. You can probably also learn a lot just by looking at the datasheets for charge controllers.

As an example, there is the MaxDS2715.

This chip is built to control the charging of up to 10 NiMH cells. It is configurable for the number of cells, includes connections for the charge current sense resistor and for a thermistor. Proper charging requires regulated current and voltage, both of which this chip provides. Among the criteria for "full charge" detection is the temperature of the cells - this chip has the needed connections for a thermistor to monitor the battery pack temperature.

You will, of course, have to provide a powersupply that can deliver enough voltage and current to the chip.

There are numerous other chips out there. Given the keywords you can find in the description of this IC, I expect you can find others easily enough. Any large supply house (Mouser, RS, etc.) should have a good selection.