(Topic ID: 282423)

Medieval Madness - LED Troll Eyes Mod - What resistor value?

By Barakawins1

3 years ago


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  • 40 posts
  • 8 Pinsiders participating
  • Latest reply 3 years ago by G-P-E
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#1 3 years ago

I'm adding 2mm led's to my trolls and followed the online directions below. I' m at the last step which is to add a 1N4007 diode and a 4.7K resistor between the 70vdc coil and leds. Instructions initially call for 4.7 k diode. However, in reading the last step, it looks like the resistor value changed to 3k6 which I'm gathering is a 3.6k resistor.

So I'm wondering what resistor should be used here? 4.7k or 3.6k. Anyone do this mod?

http://iobium.com/medieval_madness_troll_eyes.htm

#2 3 years ago

based upon the resistor value of the one he used in the picture, it was a 4.6k ohm. (Yellow, blue, black band w/ brown mulitpler and brown tolerance) You should stick with the 4.7k. I'm betting the 4.7 was "fat fingered" as 3.6 which are the buttons just next to them respectively.

#3 3 years ago

I'll hook this up tomorrow and will post my results. I'll obviously do one of the trolls first. I think you're right with the 4.7k resistor

#4 3 years ago
Quoted from Barakawins1:

I'll hook this up tomorrow and will post my results. I'll obviously do one of the trolls first. I think you're right with the 4.7k resistor

let me know how it goes. I've been meaning to do this mod on my mmr for month/years.

#5 3 years ago

One thing I will say is that it is a royal pain getting the leds mounted inside the troll head. Takes a while to align

#6 3 years ago

I think this mod really needs a bit of added thinking to assure safety and prevent things from burning up.

To calculate resistor for LED Resistor:
RL = (70V - VF(diode) - VF(LED)) / IF(LED)

Assumptions:
Coil voltage really = 70V
Rectifier VF = 0.8V (typical for a lightly loaded 1N400x rectifier).
LED VF = 2.1V. Varies with LED color and specific LED manufacturer.
LED IF - assuming using typical value of 10mA

(70 - 0.8 - 2.1)/0.01 = 6710 ohms, closest standard value = 6.8K
Power dissipated by 6.8K resistor = (6800)(0.01)(0.01) = 0.68W (assuming 100% duty cycle).
A 1/2 watt resistor will burn up if left on too long. I try to never exceed 25% of rated power so you want a 5W resistor there. Wattage can be lower if you can *guarantee* the duty cycle is low (how long the LED is on / how long the LED is off). Even with a low duty cycle then you never want to go below a 100% load rating so you need a 1W resistor. But from a safety point of view - you should not assume anything other than a 100% duty cycle (e.g. shorted driver transistor).

If you use a 4.7K resistor (as shown in photo) -- LED IF will be 14mA. Might be OK but it depends on your specific LED. I try to never exceed 10mA for most LEDs.
Power dissipated by a 4.7K resistor = 0.94W! That puppy will be burning up if your solenoid voltage is really 70V and the LEDs were left energized.

So -- what is the typical period of time that the trolls are left hoisted up (hold voltage on coil)?
And can you guarantee to coil driving transistor will be shorted?

#7 3 years ago

Edit -- forgot there are two LEDs in series so this does drop the power a tad:

RL = (70V - VF(diode) - (2 * VF(LED))) / IF(LED) = (70 - 0.8 - 2*2.1)/0.01 = 6500
Power of RL = 0.65W

Less than 5% change in power dissipation so not a lot of difference if driving one or two LED's at the solenoid voltage.

#8 3 years ago

Before I hook this up tomorrow. I'm gonna post the true coil voltage. I'm wondering if the 4.7k resistor is enough

#9 3 years ago

I dont have a MM but wouldn't,
it be easier and safer to just power the leds from a 5v bulb in the GI string?
True the eyes will always be on but it will not be visible when the trolls are down

#10 3 years ago
Quoted from pinballjj:

it be easier and safer to just power the leds from a 5v bulb in the GI string?

Yes, I think this is much easier. However, since it's a bit of task aligning the LED's and then applying silicone or hot glue to secure everything inside the head, I'd prefer the leds last a long time as I don't intend on going back in there if I don't have to. Keeping the leds lit all the time may burn them out quicker so I'd prefer they only go on when needed.

#11 3 years ago

Here are my calculations before hooking up. The troll solenoid coil voltage is 50vdc as is shown in the attached photo. My calculations are also included. Looks like
4600ohms or 4.7k is the correct resistor. GPE can you confirm?
50vdc circuit (resized).JPG50vdc circuit (resized).JPGCalculation (resized).JPGCalculation (resized).JPG

#12 3 years ago

4.7K would be right if the voltage is 50V. But that resistor would be dissipating (4700)(0.01)(0.01) or 0.47 watts. That is still way too high for a 1/2 watt resistor. The 1/2W rating is assuming the resistor is going to operate at maximum temperature which you don't want to do. Never exceed more than 50% of rated power and I always shoot for about 10-20% max.

Note that the 50V is an approx unregulated voltage and is largely dependent on his local mains voltage levels. If his solenoid voltage measures significantly higher than a larger resistance may be required.

#13 3 years ago

Ok so I installed a 1n4007 diode and 4.7k 1 watt resistor and it works well. Here’s a pic of the first troll Install. Going on second one now.

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#14 3 years ago

Yes - it will work. But what size resistor (wattage) did you use? And can you hold onto the resistor with your fingers the entire time the troll is held up?

#15 3 years ago

Done. Both trolls complete. Used a 1 watt resistor. Yes I held onto the resistor and it was not hot. Leds are nice and bright.

105180A3-BE33-4B14-8409-6469C42CB6A4 (resized).jpeg105180A3-BE33-4B14-8409-6469C42CB6A4 (resized).jpeg
#16 3 years ago

For those attempting this mod, take my advice on one thing. Do not use silicone inside the troll head to hold down the wires to the eyes. Use a hot glue gun. Don’t overdo it. Just enough to get onto the wires. Also before applying glue, tape the wires to the back of the troll head to make it easier to glue

#17 3 years ago

How about a parts list (links to where parts were purchased) or install video? Is this install on a 97 MM or a new Mmre? Ty.

#18 3 years ago
Quoted from Westsiderkg:

How about a parts list (links to where parts were purchased) or install video? Is this install on a 97 MM or a new Mmre? Ty.

This was already mentioned in the first post. See below link for install photo. The only changes that needed to be made is that a 4.7K resistor needed to be added. That's the only correction. All other parts are the same. Sourcing parts you can find online.

This is for an original MM

http://iobium.com/medieval_madness_troll_eyes.htm

#19 3 years ago

Darn....IDK if this would work on a MMR...are the application different? I know the MM and MMR use the same coil...any input from a MMR owner is appreciated...dont want to fry anything!

#20 3 years ago
Quoted from Westsiderkg:

Darn....IDK if this would work on a MMR...are the application different? I know the MM and MMR use the same coil...any input from a MMR owner is appreciated...dont want to fry anything!

I’ll be doing this at some point, but man do I have a freaking list of projects to do first....I mean I should probably clean my games :-p

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#21 3 years ago

Correction to "that's the only correction":
4.7K but rated at 1W *minimum*. At 1W, it will still be running very hot if left energized for any amount of time.
Would be better off if you used a 2W resistor for lower temperature.

#22 3 years ago

I just wish there was a kit out there for DIY folks.

#23 3 years ago
Quoted from G-P-E:

Correction to "that's the only correction":

Thanks for that Ed. Yes. I used 1W which works fine. 2W is obviously better.

#24 3 years ago

You can wire the eyes up to the flashers on the L+R of the playfield. So only running off 12v. The eyes will light up when the trolls pop up and when they are hit.

I did this on my MMR, and it looks and works fantastic.

I have since put green LEDs under the trolls so the holes glow green as well.

#25 3 years ago
Quoted from erak:

You can wire the eyes up to the flashers on the L+R of the playfield. So only running off 12v. The eyes will light up when the trolls pop up and when they are hit.
I did this on my MMR, and it looks and works fantastic.
I have since put green LEDs under the trolls so the holes glow green as well.

Looks like these are tied to the flasher domes on the left and right, is that correct?
If so, all you need are pre-wired 3mm 12v red leds, tapped off the flasher dome connectors. Seems like this is being made more difficult than it otherwise should be, but maybe I am missing something.

#26 3 years ago
Quoted from Westsiderkg:

I just wish there was a kit out there for DIY folks.

Instructions just call out generic "Red LED" but doesn't get into specifics on sizing. Based on drill bit size specified (7/64"). Way too small for popular T1-3/4 (5mm) LEDs. My guess, these would be size T1 LEDs at about 3mm diameter.

Per eyeball pair:
Qty 1 resistor, value 4.7K ohms at 2W. RMO2-4.7K
Qty 2 LED, Red, Size T1 = Avago part number HLMP1700
Qty 1 Blocking diode, part number 1N4004 (anything 1N4001 and up).

Working up an inexpensive kit for these but the resistors are backordered.
Also out of heat shrink. Looking at:
M23053/5-102-0 for leads, maybe size 103... will try both.
M23053/5-105-0 for over all
Wasn't planning on including the wire, though. I don't normally stock wire and heat shrink.

I don't like the idea of a 2W resistor being heat shrinked (cut off airflow). Looking at ideas for mounting near solenoid rather than inline splice.

#27 3 years ago

Ed the 2mm red diodes are best. 7/64 is the correct diameter drill bit. They fit nicely and when you use hot glue it seals well.

#28 3 years ago

2mm isn't a standard size. Who has 2mm?

#29 3 years ago

Here is your source for 2mm. They are ceramic led's and the white band the led is great for natural whites around the eyes look. I'm sure these are available on other sides as well. These work best.

lumex (resized).JPGlumex (resized).JPG
#30 3 years ago

My personal preference

led (resized).JPGled (resized).JPG
#31 3 years ago

... sigh.... obsolete according to other resellers.
Will check direct.

Or maybe use the 22mm version?

There's also 2mm tower style LEDs where only the tip sticks through the opening.

#32 3 years ago
Quoted from Lermods:

Looks like these are tied to the flasher domes on the left and right, is that correct?
If so, all you need are pre-wired 3mm 12v red leds, tapped off the flasher dome connectors. Seems like this is being made more difficult than it otherwise should be, but maybe I am missing something.

No, tied into the boards molex plugs right beside the trolls on either side under the playfield. I posted pics and what I used in the MMR mods thread

Could also be used right off the coils. If you change the resistor value. Would be the same length of wire.

#33 3 years ago

does anyone here where there is a constant 12vdc on MM? what location?

#34 3 years ago
Quoted from Barakawins1:

does anyone here where there is a constant 12vdc on MM? what location?

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#35 3 years ago

Thanks for all the info! Hopefully someday a member will post a step by step, with pics or video, for the MMR. Would be great seeing the underneath board soldering points.

#36 3 years ago
Quoted from Barakawins1:

My personal preference[quoted image]

Direct link to purchase?

#37 3 years ago
Quoted from Barakawins1:

does anyone here where there is a constant 12vdc on MM? what location?

Presume you are talking about the original. J139-j141 have 12v. J140 should be open.

#38 3 years ago

Has anyone attempted this with constant current diodes?

#39 3 years ago

Current Limiting Diodes (CLD) never really got popular as you can do the same thing with cheaper components (simple FET and resistor) or just a resistor since minor variations are acceptable.

On the plus side - CLDs can give you a much more stable current regardless of differences in source (solenoid) voltages... not that anybody's eyes could notice the slight deviation in LED brightness from one machine to another.

But - these have too many disadvantages to them:
CLDs in a low input voltage & low current application work well but when you start increasing the input voltage & output current, they become less attractive. I haven't researched them for all variations but most CLDs that can survive this high solenoid voltage cannot put out enough current.
You would probably have to parallel multiple CLDs to get sufficient current for the LEDs in this application (I would shoot for 10mA).

CLD's are a also linear circuit which means you get lots of heat - just like the current limiting resistor method.

You still need the blocking diode (1N400x or similar).

And using a pair of CLDs such as the E562 per LED would cost about 50x more per LED with no real gain in functionality.

#40 3 years ago

Ya know - Barakwins1 may be onto something with post #33.
Why go complicated with the large resistor and only turn on the LEDs when the head is up.
If the head is down and the LEDs are still on... who's gonna know?
Just use a low voltage with a much smaller resistor and leave the LED on full time.

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