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Comment by hn_throwaway_99 | Hacker News Reader

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hn_throwaway_99

I think this is neat, but only in a Rube Goldberg machine sort of way. The instructions are:

1. Open the scale

2. Rest your finger on the trackpad

3. While mainting finger contact, put your object on the trackpad

4. Try and put as little pressure on the trackpad while still maintaining contact. This is the weight of your object

That is, the pressure sensors only work if it detects capacitance, so you need to be touching the track pad (but not too much!!) while weighing something.

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This is a very clever hack, exactly the sort of thing that belongs on Hacker News.

Could a small piece of conductive foam or some cleverly layered tin foil+paper work? So put the object on the shim (which has a known or even negligeable weight)

Could probably make a small stand with nubbins from touch screen pens as the feet.

No, you need roughly a small human's worth of ground mass for most capacitive touch sensors to register a touch.

Tape a wire to the trackpad and hold the wire?

How do capacitive pens work?

You electrically couple to the pen, unless they are active devices, in which case they generate a signal.

That can't be, they work with gloves and things. My gloves even have a thing at the end that works with the touchscreen.

You’ll have to be more descriptive for me to have any hope of answering.

If by your gloves have a thing at the end you mean a patch of special fabric, yes, that fabric conducts from your skin to the screen.

ground mass?

If you don't have ground human presumably you can substitute ground beef or ground turkey.

I once put some aluminum duct tape completely over the touch pad of an old laptop to see what would happen. Turns out it induced enough "eddy currents" to make the mouse move around the screen without me touching it--in a way, visualizing the currents!

I connected the foil to ground using a small strip of the tape to the ground metal of a USB port on the side and it disabled the touch pad.

Looking back, it would have been interesting to code up a program to record the movement of the mouse as a trail of pixels...

If you ever want to do this keep in mind to reconfigure the mouse as a digital pointing device (tablet like), otherwise the mouse acceleration will mess up your position measurement.

On iPhones at least a hack was to rest a metal spoon on the screen and weigh something in the spoon...

Sometimes you can get capacitance to be detected if you hover your finger just millimeters over the trackpad

Could you accurately weigh a hot dog?

No, only cool ones.

I use a similar approach to weigh objects using gym weighing machine. It doesn't trigger unless there's skin touch.

Can’t you get capacitance with a wet sponge? Like your typical dish cellulose sponge. You could make a small platform?

I remember drawing on my old iPad back in the day by shoving a wet q-tip into a BIC pen and using it as a stylus. I am sure something similar could be rigged here

I've used carrots and cucumbers as a capacitive stylus while wearing gloves.

It's the reason why I love Note and S Ultra phones - the stylus. I'm using it now.

The recipe was on your phone/tablet and there was no way you were taking your gloves off?

Nice. No, I preemptively armed myself with a carrot before taking the dog for a walk in cold weather.

I only had a non-stylus smartphone for a year and a half before whimpering back to the Note series. It's what keeps me in the Samsung sphere of influence.

I used my nose.

I've done that many times while working on something and my hands are filthy.

My nose-eye coordination leaves something to be desired.

Ever try putting gloves back on when your hands and the gloves are both wet? This is why I print recipes on the laser, and just take the paper version downstairs.

I use this to avoid touching the stupid self-checkout machines when buying groceries

What do you use to avoid touching the carrots and cucumbers?

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