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Thomas the tank engine. TTTE.


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Mr @kress I'd be happy to redesign the mosfets as they appear to be troublesome.

I'm running 28 to 32vdc through my coils and it will be just a 5v output from the arduino or a buffer chip to switch them.

 

Mosfets problematic...Pfffft who would think it....Im already thinking of the Grunta's Super Duper Coil Lock on due to transistor or Mosfet fail circuit......Mmmmm I love the smell of coils cooking in the morning !:redface

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Mosfets problematic...Pfffft who would think it....Im already thinking of the Grunta's Super Duper Coil Lock on due to transistor or Mosfet fail circuit......Mmmmm I love the smell of coils cooking in the morning !:redface
I didn't mention any names.[emoji38]

 

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FETs are just bad design. Yes they work well when all is well but to many outside factors can make it not well, many static.

 

You can blow them open or closed and if you blow a hole through the wafer, you can get the switching voltage straight through them and back into your driver circuitry.

 

FETs were actually designed before transistors but basically sat in the shelf because of these shortfalls in there design but are now being used because of a lower parts requirement which means lower cost and overall smaller size in board design.

 

Of all the driver circuits I have seen I like the Bally SS design for one small part as said here....

 

The computer program that runs the machine also tries to limit this spike by turning off the coil near the zero crossing of the AC line. This helps because the DC that drives the coils is rectified, but not filtered, so it's not smooth DC, but "humpy", as shown in the adjacent picture.

By energizing the coils just after the zero crossing, the in-rush of current caused by a coil is limited. By turning the coils off just after the zero crossing, the voltage spike caused by the collapsing field is also kept to a minimum.

 

This is a small exert from this story here....

 

http://www.publicgames.com/viewtopic.php?t=158

 

Seeing as you are writing your own software you could use it to drive a Bally SS Solenoid Driver Board and let that board do all the coil switching for you.

 

It could be one part you don't need to build from scratch and can drive 19 coils, supply 5vDC and 190v but you're not going to use that part.

 

Best of all if it fails and most failures are in the secondary side or power switching side of electronics, you can easily repair it or replace it. Also these boards have 3rd party replacements available.

 

One thing Bally never did but is quite possible to do is use these transistor circuits on these boards to drive other voltages as long as those other DC voltages share the same ground.

 

If for example you want to drive a 12vDC device using one of the transistor circuits, power the device on the machine with a +12vDC supply rather than the normal 43volts common + rail and providing the +12vDC supply uses a common ground as the 43volts, the transistor will quite happily switch the 12vDC device exactly the same.

 

This last part I will be using on my HomeBrew because I want to drive 5vDC, 12vDC and 43vDC parts.

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Trying to get the engine shed artwork to match the precut wood took a lot of fiddling and trial prints but it's done.

I also created a mask for the multiplier inserts and a template for the laser cut plastic cover.

Next are the plastics. I've already done the Helipad for Harold but there are a few more to go. And the large one that covers the whole playfield.f7bf110a4906b7c22c31c1f14e3ae551.jpg970518e7e14cc19d936196a3f2bbbc27.jpg00a1e9ff973fa9f17f936485b7237479.jpg

 

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Thomas the tank engine. TTTE.

 

I scanned the plastics and used them as templates for the artwork. I think I've got a method sorted now.

Slings are done so far. You can probably tell, I'm no graphic artist.[emoji16]

That's it for today.

Cheers Trev

605d4ca071025bef102ce5ae89d829de.jpg45bdc4573d3cf75d572b39180e4ee554.jpg

 

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I might have missed this previously, but what material & thickness are you using for your plastics?

 

Great work so far!

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I might have missed this previously, but what material & thickness are you using for your plastics?

 

Great work so far!

Thanks

It's 3mm polycarbonate. I made the smaller plastics from the offcut from the center of the large plastic with the track on it.

 

 

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This is one part of building the machine I find very difficult. Artwork. I'm so grateful to @stuzza for doing the cabinet and playfield art.

I've got three more small plastics to go and then it's time for the big one.

Of course I had to put Trevor the traction engine on there somewhere, eventhough you won't see much of him as he's hidden by the big plastic with the track.37f079a4a6a798093b3378b8491689e1.jpg

 

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I'm going to say this again PINBALL SWITCHES LOW

 

Unless you want a flaming wreck

 

There is something I'm not getting here. A switch can get stuck in either position. It can not activate when it should (be stuck permanently off), or it can activate when it should not (be stuck permanently on). So, I would have thought whether you designate the on or the off position as "active" is arbitrary? Either way, it's wrong some for some fault condition.

 

The way I see it, for something that needs to be pulsed, such as a slingshot coil, the only defence is to handle the issue in software. Pulse only after the software has seen another state transition so, if the switch gets stuck either way, the coil will not activate again. No fires that way, as far as I can see?

 

Michi.

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There is something I'm not getting here. A switch can get stuck in either position. It can not activate when it should (be stuck permanently off), or it can activate when it should not (be stuck permanently on). So, I would have thought whether you designate the on or the off position as "active" is arbitrary? Either way, it's wrong some for some fault condition.

 

The way I see it, for something that needs to be pulsed, such as a slingshot coil, the only defence is to handle the issue in software. Pulse only after the software has seen another state transition so, if the switch gets stuck either way, the coil will not activate again. No fires that way, as far as I can see?

 

Michi.

 

Having a switch go to ground when it's closed helps eliminate spurious readings due to voltage spikes caused by coils etc it has no effect on wether a switch is stuck closed.

If the switch is high when in the off state and a spike is encountered the spike has no effect as the signal is already high.

If a switch is low in the off state and a spike is encountered it will trigger a reading as the voltage will change from low to high without the switch being closed.

My code will detect when the switch has changed from high to low (closed) and sends a pulse to the coil through a 555 timer and transistor circuit which energizes the coil long enough to pull in fully.

It will then look to see if the switch has gone high again (opened) before it will allow the coil to be fired again.

So if the switch is stuck closed the coil will only fire once for a predetermined time set by the 555 and not fire again until the switch fault is rectified.

Well that's the theory anyway.

 

 

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Having a switch go to ground when it's closed helps eliminate spurious readings due to voltage spikes caused by coils etc it has no effect on wether a switch is stuck closed.

 

Ah, OK, thanks for that! I was just reading things wrong, my apologies.

If the switch is high when in the off state and a spike is encountered the spike has no effect as the signal is already high.

 

Yes, that makes perfect sense; you don't have a floating circuit that way.

 

So if the switch is stuck closed the coil will only fire once for a predetermined time set by the 555 and not fire again until the switch fault is rectified.

Well that's the theory anyway.

 

 

Well, that'll be it in practice, too, I would think. It'll just work.

 

I guess similar idea could be used to stop oscillations as well, such as when you have a sling with the switch contacts too close, and the vibration from the sling firing causing the next switch closure. You could count how many times in the last n seconds each switch has triggered. (Just keep a counter for each switch in an array.) Then scan the array every five seconds or so from a timer task and check whether there is an unreasonable count on any of them. You'd have to tune this a bit, to deal with multi-balls where a lot of stuff can happen in a short time. But it should effectively stop this kind of thing, especially for slings and pop bumpers.

 

Michi.

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So much useful information in this thread. I am loving it... I do wish I understood it though.

 

Have a read of things like Bally's Theory Of Operation and the William's WPC Theroy Of Operation and it helps understand exactly the problems encounted on pinballs.

 

Electronics used in pinballs is some of the most technically demanding because it is one of the harshest environments to use electronics in with the vibration, EMF created by coils turned on and off, dust and heat. Add to this all the connectors where low voltage is likely to encounter voltage drops and you get a good understanding on why precautions need to be designed in on the circuitry.

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Having a switch go to ground when it's closed helps eliminate spurious readings due to voltage spikes caused by coils etc it has no effect on wether a switch is stuck closed.

If the switch is high when in the off state and a spike is encountered the spike has no effect as the signal is already high.

If a switch is low in the off state and a spike is encountered it will trigger a reading as the voltage will change from low to high without the switch being closed.

My code will detect when the switch has changed from high to low (closed) and sends a pulse to the coil through a 555 timer and transistor circuit which energizes the coil long enough to pull in fully.

It will then look to see if the switch has gone high again (opened) before it will allow the coil to be fired again.

So if the switch is stuck closed the coil will only fire once for a predetermined time set by the 555 and not fire again until the switch fault is rectified.

Well that's the theory anyway.

 

 

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Don't you use "pull up" or "pull down" resistors

(which ever suits your switch logic)

So no inputs are floating

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Having been an electrician for a number of years, all my fault finding was with switched actives, the neutral is always the common.

I found it difficult, and still do, to work on electronic equipment and pins as I'm not used to thinking that the ground line is switched.

It's kinda like thinking mirror image to me.

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I guess similar idea could be used to stop oscillations as well, such as when you have a sling with the switch contacts too close, and the vibration from the sling firing causing the next switch closure. You could count how many times in the last n seconds each switch has triggered. (Just keep a counter for each switch in an array.) Then scan the array every five seconds or so from a timer task and check whether there is an unreasonable count on any of them. You'd have to tune this a bit, to deal with multi-balls where a lot of stuff can happen in a short time. But it should effectively stop this kind of thing, especially for slings and pop bumpers.

 

That kind of logic can cause issues too. For instance on radical, there's 3 switches in the lock Lane. When one ball is already locked, if the top switch closes, the kicker fires, and the locked ball knocks the incoming ball out of the lock Lane before returning to rest on the bottom switch. It's pretty cool.

 

Unfortunately, if you manage to backhand the ball back into the lock Lane immediately, the top switch is ignored as a bouncing switch, and you end up with both balls locked when you shouldn't.

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  • 2 months later...
  • 3 months later...

Slowly getting back in to it. I've got some money now to get the playfield and plastics printed so I'm starting to do the artwork for the plastics again.

Cranky and the windmill are new only two more to go.

Cheers Trev 375acd9d681a084fc08123994951920f.jpg

 

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