Post-Photo Booth

Since finishing the Halloween Photo Booth project (a month of work for three hours of "show"--gotta love Halloween), I've been busy doing a major revision to my Reactor plugin for the Vera. But I'm now in late beta on that update, and with the Christmas break approaching, there will be time to spend on some of my other ideas.

Two ideas came up in the Halloween Photo Booth project that I already have out in schematic form--I just knocked them out quickly to see what a solution might look like. Hopefully, over the break, I'll have time to lay out some boards.

The first is based on Adafruit's DC and stepper motor control HAT for Raspberry Pi. They use a 16-channel PWM chip that uses I2C to communicate with the processor. The chip offloads the processor from any software PWM, and expands on its limited hardware PWM. Although we didn't do much PWM light control in the Halloween Photo Booth, I can see the need for it in future versions, so I thought, why not build a board with 16 channels of hardware PWM for that job? So, using the same PCA9685 PWM driver, I've laid out a control board with opto-isolated inputs like our 4-channel design, and insertable "driver" boards to handle the higher (than logic) voltage and current of the LED circuits. The system allows control of up to 8A per channel to a max of 12A total on all channels simultaneously (that's 144W of LEDs at 12VDC--quite enough for anything we might do in a photo booth). I'm calling this project "LightShow16."

The second idea, which I call "PiUPS," originated with trouble we had, albeit briefly but with some lingering concern, about getting an adequate 2.5A power supply into the Pi. The Dupont wires we were using just didn't give us good connections consistently, and we ended up using the USB input, but that felt kind of "how ya doin'" as Dave Jones would say, because it really would only deliver 2A of the full 2.5A the Pi could theoretically draw. The Pi's GPIO header has two 5V pins, plenty to deliver 2.5A, so pretty much any kind of HAT with a solid connector could present opportunities to get a better power connection. That thinking quickly led to getting some ride-through when the power supply fades for whatever reason, and that gave birth to PiUPS. The board is a HAT (Hardware Attached on Top) that connects to the Pi's GPIO header and provides power to the Pi through the 5V pins. It has barrel and terminal block connections for input power. The input power feeds both the Pi and an on-board charger for a LiOn or LiPo battery. When input power fails, an on-board boost converter capable of a full, sustained 3A output draws from the battery and supplies 5V to the Pi. An optional GPIO connection signals the Pi when the battery is approaching the low-voltage cut-off point (i.e. in time for an orderly shutdown). The board can simultaneously supply the Pi and charge the battery when provided an input supply of 3A or more (or at least 500ma higher than the demand of the Pi). Accessory connectors allow supply of 5V to other system components if needed. A 2500mAh battery should be able to run a fully-loaded and very busy Pi for up to an hour.


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