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Detailed Arcade Switch Testing

2017-12-30 18:55 - Gaming

As mentioned, I converted my button tapper machine to also test the buttons being tapped. Since that I revamped it to get slightly more accurate readings, and now I have interesting data to report. Beware the wall of text, but delight in the pretty graphs in the middle.

Methodology

See the linked post for a description of the raw data format. For each switch type, it's 250 events each pressing the button down, tracking the state of the switch over time, releasing the button and tracking again. All real physical switches will bounce as their contacts strike each other and spring back, only eventually settling to really be closed (or open). Each particular (model of) switch will bounce more or less, based on how it's built. With the raw data in hand, for each switch and event (press or release), I measured a virtual point at every microsecond, counting for each of the 250 tests, was the switch opened (0) or closed (1) at that point. Then take the average closed-ness, at every microsecond, for each switch and event.

So in the graphs below, a line at the bottom (0) means the switch was always open at that microsecond, and at the top (1) it was always closed. Anything in between means it was sometimes open, sometimes closed, at that microsecond. Across 250 tries, this averages out to a nice visual representation of how quickly, on average, the switch closes or opens, and how it acts while doing so.

The Switches

In alphabetical order, by nickname. Nickname is the short form I'll use to refer to each of these switches, going forward. With the nickname, you can look above to see exactly what I mean, but hopefully otherwise avoid bias ("I'm a fan of brand X!"). Activation force is the "gram force" required to activate an idle switch. Cost is the price each, to buy quantity ten.

The LS switches were mixed in my pile of spares, where I save even bad/removed ones (sometimes the next bad one is worse, and you've got no good spares, and you don't want to wait for shipping for a replacement!). Most are visibly used, stained (drinks/spills?), which shows easily on their white plastic body. Comparing limited known properties, I'm guessing this is a LS0851500F100C1A but I could be wrong there. I left question marks in the table, because I have to guess at the various values as well. As best I can tell, actuator 00 is the bare pin (definitely matching this switch), and that comes with a minimum 100gf activation.

Also worth mentioning is that the VM5 switches were described by everyone I can remember as being unsuitable for play, immediately upon installation while brand new. We'll see why shortly.

Button Presses

1C22 1C23 D449 LS V71D V73A V75F VM5 (Hover above links to isolate their graph.)

There's eight switches on the graph. To my eye there's an obvious cluster of four near the left (don't miss the yellow one), three in the middle, and one outlier off to the right. A theoretically ideal switch would be a vertical line straight up at microsecond zero, but we're in the real world. My testing machine takes time to charge up the solenoid, time for it to move, and time for it to overcome the force of three springs (one built into the solenoid, one in the button housing, and then the one in the switch itself). That's the twelve-ish millisecond delay before any of the lines on the graph start to climb. And then real world randomness means that each trial happens at a slightly different time. That and the randomness of the bounces determines the slope of the line. Being closer to that theoretical straight-up line towards the left of the graph indicates a "better" switch. So how close does each one get?

The most critical thing is really the moment where the switch is done bouncing and is always closed. So I'll go in the order that I see them touch the top of the graph. First is the dark blue line (the V73A) which fully activates (here, this means time from the earliest to the latest reading across all 250 samples -- worst case) within 4.5ms of the first moment that it starts. Next is the yellow line (the V71D) with a nearly identical slope, and right behind it is the green line (the 1C23) which takes about 5.5ms. The light blue line (D449) finishes out this group at 6ms.

For all practical purposes, these buttons are identical. We'll have to look at some minimally processed data to tell them apart. Three of these bounce only two or three times typically (seven or eight worst case), only the V73A is bouncier. They all typically finish bouncing in well under two (or one!) millisecond, and the worst case (individual sample) is still under three milliseconds. They're all fine buttons, with the V73A being slightly towards the bottom of this pack.

So for the group in the middle: Purple (1C22) is the first of these three, taking 7.5ms. Red (V75F) is next with orange (LS) both taking 7 to 9 ms. A second glance at the data shows however that these three bounce many more times, with worse average and maximum single sample times bouncing.

Finally there's the outlier which forced me to zoom the graph way out: the VM5. Excepting the worn-out LS, it's a full two or three milliseconds slower to start the process of switching. But it has a timing spread from there of another 35ms, with lots of bounces and a 24ms worst-single-sample time to settle. This one is completely unacceptable. A simple "wait 20ms and then see what state the button is in" approach (which is exactly the sort of thing a simple debounce system might do!) will accidentally read the not-pressed bouncing state sometimes! This lines up perfectly with the real play experience with these switches: they're just not reliable enough.

So can we use data to explain where these lines fell on the graph? I think so! The first "good" group of four have activation forces of 50, 150, 49, and 76. The other four have activation forces of 25, 15, 100 (worn out), and 20. Again excepting that one worn out model, it's clear that the higher weight springs produce a more reliable button.

Button Releases

1C22 1C23 D449 LS V71D V73A V75F VM5 (Hover above links to isolate their graph.)

Releasing a switch is much easier than pressing it. So all switches tested have significantly fewer bounces on the release, and activate more quickly. There's not really much more to say here. This isn't an important criteria.

Subjective Experience

I installed all these switches into the local arcade cabinet and asked players to let me know what they thought of all of them. They all played okay, so there was only one consistent bit of feedback: despite one player who loved it, everyone else commented negatively about the 150gf V71D. So despite a heavier spring producing better looking data, we know that we can go too far.

Results?

The one thing to say for certain is that the model of replacement switch matters! Any name brand should do fine, and 50-100gf activation seems to be the sweet spot. Optimize for cost within that range. I'm interested in trying the LS in a non-worn-out state!