Air Plugs

A project log for Solar filament drier

How to keep filament dry while being too poor to afford electricity.

lion mclionheadlion mclionhead 01/19/2022 at 03:420 Comments

Burned $60 or twice the cost of a roll of TPU to get this started, not counting spare parts.  The AHT20 sensors have a single fixed address which requires 2 I2C busses.  We thus have 5 required pins:

1 MOSFET push pull, 4 I2C open drain.  The MOSFET opens the valves & fires up the pump.

The AHT20 burns 3-5V.  The fruit board has its own 10k pullups.

The pump burns 4.5-5V 500mA.  The 'fruit says it's not rated for continuous use, but the datasheet says the 50% duty cycle was only a test condition.  More likely, it has the same lifespan of any brushed motor.  The 1.8L pump would need 2 minutes to fill the container.

The valves burn 5-6V.  Higher is better.

The brain burns 3-5V.

The fan burns 12V.  It's a job for a dollar store USB charger, now $1.25 Biden Bucks.

The AHT20's have to be ventilated, so that means the fan + sensor would be a single module inside the container.  The other sensor goes in part of the room near the air inlet, but not directly on the container since it gets hot.  The air inlet & outlet have to be separated.

After many test prints & test holes in cheaper tupperware, the plugs were finally installed in the expensive piece.  Silicone doesn't adhere to plastic, but it tries to seal the gaps.  The plug sandwich is then CA glued.  They come off with pliers.  The tube fits tightly enough to not need any more sealant.  This was about the best air plug a lion could come up with.  It's never going to be air tight in the long term.  Expansion & contraction of air is going to force itself through.

Heating the PLA with an air gun was enough to bend it to fit on the curved surface.  PLA is not the ideal material for something which is supposed to get hot, but PETG couldn't bend & PETG couldn't adhere to itself.  TPU might have adhered to itself with some hot air welding, so the plugs might get replaced once the TPU is dried out.

It may be all the air sealing & humidity sensing is unnecessary.  It might be good enough just to have a fan in a container.  The lion kingdom believes it is necessary because the window gets humid at night.