Took the prototype to circus practice today, then my daughter and I went shopping where I kept playing with it, cycling through some random images, some of which are using a full 100% duty cycle burst (full white), and others that are less. I’d say all in all I had it running for about an hour, at full brightness. This is the current battery level. Range is 2.8V to 4.2V across all 48 pixels (end to end.) Not bad.
@Larry1 @Matt_Starbuck
Not bad at all sir!
Aaaand the sucker is charging fast. With 12V DC-IN, it charges at 2A compared to the 500mA when connected to a USB cable.
The dual-mode charging is sweet. That is a great way to get around that particular engineering challenge. Good thinking.
How big is your 5 V step up converter?
1A, don’t need any more than that. I’m not driving the LEDs with it.
The idle current on those 8806s is very useful when the pixel duty cycle is at least partially black. A definite advantage over the WS 2811
You’re driving your strip directly off your battery? I thought that you were all for color fidelity and won’t that varying voltage destroy that?
I cut off the phantom current with Szlikai pairs. LPD8806 work stable from 5.5v down to 2.7v and I cut it off at 3v. No issues.
Why the npn/pnp pair and not a fet? size?
Because I want to cut off VCC, not GND. Each pair is 4.1A, there are four pairs total.
If you only cut off GND, you will still have VCC leaking through the IC and out the data lines to the LED. Hence cutting off VCC is the better way to go.
@Ashley_M_Kirchner_No , can I ask why you need the 5V step up? the AVR should be good down to and below your 3V cutoff.
Also why not just go with a high power USB charger (from a tablet) and save space on the DC-IN connector?
Very neat trick with the battery level by the way, yet another thing for me to think about.
Because I’m running the AVR at 16MHz and that requires at least 4.5V for stable operation. And using a high power USB charger will have zero effect as the charging IC itself regulates whether it charges at 500mA from a USB connection or 2A from DC-IN.
Oh OK that makes sense, I still gotta do quite a bit of testing yet with regards to the power side of things so I guess I’ll probably end up needing one in the end.
So to get rid of the DC-IN would mean a new device and design then so it makes sense to stick with it. My charging IC is pretty dumb and has no clue where the input is coming from so I can get away with the USB, it chugs along nicely at just over an Amp.
I also stick with correct specs. USB2 is specified at 500mA. USB3 is up to 900mA, USB3.1 is 2A/5V, 5A/12V or 20V. Since I’m sticking with the smaller USB2 connector, the charging IC only allows up to 500mA through USB. There’s something to be said about using a proper circuit design with proper components. Something the Chinese can learn from.
Also, the charging IC I’m using has all the monitoring functionality built-in, all I have to do is feed it power. It takes care of the rest, monitors the battery’s charging rate, voltage, everything. Makes for a simpler circuit in the long run.