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I'm trying to measure the actuation force of buttons on the Playstation Vita, in preparation of building an external device that presses these buttons automatically. Specifically, I'm trying to measure the force required to push the buttons on the D-Pad on the left, and the action buttons on the right.

Googling "how to measure actuation force" will give you pages of results of mechanical keyboard enthusiast forums, and they often mention measuring the actuation force by stacking pennies / whatever coins you have until the key is depressed and the computer recognises the keypress. I can't do that normally here, since the buttons are really small (<1cm for the action buttons) and even the smallest coin my currency has cannot be stacked onto it without toppling over.

In an attempt to mitigate the problem, I made the following setup. It still uses coins as weights to push down the button, but I rested the coins on the ruler that in turn rests on another object of somewhat equal height/thickness to the game console, in this photo, the remote control seen in the background. I conducted the experiment by continuously adding coins with a game running on the console until it registers a keypress, and then summing up the weights of the coins.

experimental setup

However, the results are rather inconsistent and questionable. I repeated my experiments several times (by knocking down the coin tower and stacking it up again) as standard practice, and I got values ranging from 100g to 180g, which feels extremely high for buttons on a handheld game console, and that large spread seems to be telling me that my experimental technique is just plain wrong.

Some possible causes of inconsistencies from the setup:

  1. The coins are not the same - I'm stacking 5 different coins at once
  2. The coins are not stacked in the same order each time I redo the experiment
  3. The center of the coin tower is not aligned with the center of the button on the game console - I don't know how to do this without the coin tower making contact with the neighboring buttons or it toppling over

Some steps I have taken to possibly improve accuracy:

  1. The ruler used is a stiff metal ruler and does not bend significantly
  2. The ruler is kept horizontal
  3. The only points of contact of the ruler are the remote control seen in the background and a single button on the D-Pad.

TL;DR: How can I improve the accuracy of my setup, or other better ways to measure actuation force of such small buttons?

Update & Final Results I used the weighing scale method, and the results are 80g for the D-Pad and about 120g for the action buttons on the right. Thanks everyone!

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  • $\begingroup$ Have you got any small washers? Closer to the diamter? Or put the pad on a set of electronic scales? $\endgroup$ – Solar Mike Aug 6 '17 at 17:32
  • $\begingroup$ I don't have small washers, but they are probably too light for my requirements. Closer to the diameter will make the coins dangle off the edge of the ruler, causing it to topple after stacking 5 coins or so. What do you mean put the pad on a set of electronic scales? $\endgroup$ – chesnutcase Aug 6 '17 at 17:34
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    $\begingroup$ So, put the device on the scales, use tare to zero then push on the button gently and watch the reading to see when it operates. But repeatability and scanning frequency of the scales may be a problem... $\endgroup$ – Solar Mike Aug 6 '17 at 17:37
  • $\begingroup$ Good idea, but are kitchen scales sensitive enough for this? I don't have any lab equipment. $\endgroup$ – chesnutcase Aug 6 '17 at 17:38
  • $\begingroup$ My small one only goes to 5kg max but measures in grammes... $\endgroup$ – Solar Mike Aug 6 '17 at 17:44
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If you want a quick and somewhat inaccurate hill-billy engineering answer, I would take a digital kitchen scale and place the PSV ontop of it, tare it, then load up a program to test the buttons (game, menu, etc). with the scale device zero'd out, slowly depress the button until it is read by the program. a full actuation can and will differ from the triggering of the circuit. Wait for the program to read the triggering rather than the button's actuation, and add a few extra grams to it.

If you want a precise measurement... I have no idea what you have available for building as far as "home equipment" is concerned.

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    $\begingroup$ This is similar to SolarMike's comments. The one thing I'd add is: make at least 10 measurements, and if the median and average are not close to each other (or if the standard deviation is large-ish), take a lot more measurements until the data "smooths" . $\endgroup$ – Carl Witthoft Aug 7 '17 at 19:47

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