This is for other Ghostbusters Props that don't fit into the categories above.
Hot off the heels of my K.U.D Meter I figured I'd try my hands at making a replica Radiacmeter. I gather they are reasonably easy to find in the United States but less so here in the UK. So I'm going to need to make one myself.

While I source some of the other materials such as an appropriate shell (I've found someone who is willing to make a resin cast of their own) and some other components I thought I'd begin experimenting with controlling an analogue gauge with an Arduino using the skills I gained making my K.U.D.

Using the measurements someone helpfully took of their own Radiacmeter and posted to the Ghostbusters Reference Library I've identified a suitably sized analogue voltmeter.


Alas, it looks nothing like the real screen.


However, the voltmeter I've ordered from Amazon can be taken apart and so I should be able to print off a new graphic to go in place of the old one. I've commissioned someone from Fiverr to turn the Minirad screen into a scalable vector graphic so I can resize and tweak it to fit. My running plan is that this can be glued inside the shell of the device so that it fits where the window is. As this will be recessed back in the shell I may need some additional acrylic to go on the surface but it kinda depends on how this resin shell turns out.

Sample image from Epic-Props (mine hasn't arrived yet so I don't know how much cleaning up will be needed)

Once again I'll be using an Arduino Nano to control the device. This is because I can use the analogWrite function to make the needle twitch. My current circuit consists of a 9V battery which is connected to a latching push button which I will put underneath the 'Test' button to effectively act as an on/off switch for the Arduino. The 'Read' button will be a momentary push button (i.e. it will only work when the button is held down) which will trigger the microcontroller to twitch the needle madly in the yellow/red areas. When idle (on but the 'read' button is up) then the needle will jiggle at the very low end of the green area to represent some sort of slight background radiation/spiritual presence. The real device has no sound but I might add a high pitch tone if there's enough room.

This is my Tinkercad project so far: ... adiacmeter
Last edited by Mercifull on April 12th, 2023, 9:39 am, edited 2 times in total.
Nighty80 liked this
My commission has come back from Fiverr. Neets a bit of tweaking and tidying up but I can do that myself in BoxySVG. It will also need scaling slightly different to the real screen to match the low and high needle positions of the voltmeter I've got.

I ran out of revisions on fiverr and figures I could tweak the rest myself such as tidying up the little white identifiers for the levels, the angle of the text around the arch and the low/high lines. I'm not bad at tidying up in my svg editor I just didn't really know where to start to make the initial draft (hence going to fiverr).

Lol on closer inspection the file I got from fiverr is trash. It looks on at first to the naked eye but when you look more detailed or use rulers to check lengths of lines etc it’s a mess. The image I sent has just been traced with no logic applied to straighten it up or keep it symmetrical etc. So it looked is like I’m going to have to make it again myself from scratch. At least the Minirad logo is usable especially as that’s something I probably can’t do due to its complexity.
A small update. I’m struggling to find a suitable voltmeter that will fit into the shell of the fake radiacmeter. For some reason (possibly to aid the manufacturing process by using the same components across multiple variations on the voltage readings) it’s too deep/thick to fit. I’m going to see if I can shave a few mms here and there by taking off the old plastic screen and by cutting as much plastic off the very back as possible. If need be I could also 3D print a new housing for it. Alternatively I need to source a thinner gauge. I keep looking at my basic battery tester and wondering if one of those could be repurposed. If I can’t get this original voltmeter to fit I’ll open one up and see if I can bodge it to work instead. Just setting a pin Arduino pin to analogWrite 255 and using probes in the + and - only moves the needle about 20% of the way but I’m assuming there’s some resistors in there which are affecting that.
Despite shaving off as much of the plastic from the back of the voltmeter housing as well as sanding back the rains Ed screw holes I just couldn’t fit it in the shell. A shame because it would have been a nice fit visually.

So instead I’m Going down the route of using the gauge in The battery tester. It’s smaller but has plenty of room to fit. And I can make the arc of the screen graphic bigger (but screen inaccurate) to make it look better.

I’ve started remaking the screen graphic to fit the full width of the gauge. It means that the minimum and maximum needle points won’t be quite at the start and end but that won’t really matter.

I’ll also need to design and 3D print some sort of holder for the gauge and switches that will slide inside the shell.
Test fit of the graphic with the smaller voltmeter. It’s a shame I’ve had to shrink it down but it’s not too bad. But there was just no way to get the larger one in there. The other component was just too thick

Arc graphic still WIP

I’ll definitely make some sort of cradle or holder that will slip into the casing of the shell so that I can ensure it’s fixed in place.
Fairly comfortable with my graphic now.


Given the amount of space I've got at the edges I might move the 0 and 200 a bit wider away from the arc. The black/yellow hatching is the "danger zone" i.e. thats where the needle mechanism is so nothing can go there.
Dioxide liked this
I've been looking at this all evening trying to work out how I'm going to fit all the components inside and where I'm going to put a battery. My original concept of designing some sort of slide in enclosure might still work, but I'm going to try first of all gluing a couple of layers of EVA foam together and making just a rectangle of foam for the inside. Then I'll carve into it with a knife to find locations for the gauge, momentary switch, Arduino nano and battery.

Because it's a resin cast of the real thing it has elements I don't care for. The slide in unit which presumably on the real device is the battery and brains etc is too big for me. It takes up virtually the whole space inside. I can easily shave off half of that chunk of resin and it will still screw together nicely. Then the bottom cap has these compartments splitting it up. I want to carve them out so I can use it to fit a 9v square battery to power the Arduino. I'd really like to make this something "alive" but ultimately if I end up just making it a dumb prop then so be it... not defeated yet though. Tomorrow we play with foam.
This afternoon I started trying to see what might fit where. I cut a chunk of resin away from the middle section that slides inside. In doing so I’ve been able to fit the needle gauge and arduino nano (although I have needed to clip the pins a bit). Not sure I’ll be able to get a push button in there yet, I’ll see. I also need to carve out a bit more in order to fit a 9v battery. I wanted to have a manual on/off switch as well but there’s just not enough space to work with. I shall persevere.
RedSpecial, Nighty80 liked this
After some experimenting I believe it's possible to fit in the mini voltmeter (a little more miniature than I'd have liked but I can't find a component that's closer to the screen width but still thin enough to fit inside), the Arduino Nano and a push momentary switch under the "read" button. The battery (a regular 9v) can fit in the very bottom section with a bit more drilling out of the middle section. What I'm struggling with is how to also fit in an actual on/off switch so I don't have to unscrew the bottom to put in a battery each time I want to use it. If I can fit a latching on/off push switch in there I'll put it under the "test" button.

I think my graphic still needs a bit of work. The arc is a little flatter than the direction of the needle so I'm going to tweak it a little bit more perhaps. It depends if in doing so I still leave enough room for the numbers/digits to show and not be too high or underneath the lip of the screen opening.

Worst case scenario I'll just stick in the voltmeter that's wider and not have an Arduino or anything fancy just have it as a static prop. I can see why nobody else appears to have attempted anything like this before haha.
Through grit and perseverance, I managed last night to fit the original, larger, voltmeter into the shell of the Minirad. It's basically wedged between the nuts at the top and the bottom of the voltmeter and causes a slight bulge in the middle. but it's not really noticeable unless you look really close. I'll need to use globs of hot glue to hold it into place but it should stay in there nicely.

I'm quite pleased because I was never truly happy with the smaller battery tester meter because it was so much smaller and, while I could have been crafty with the graphics going beyond the min/max of the needle, it would have always been in my mind that it could have been better.

Now the downsides... it means there's very VERY little room for a microcontroller now. The nano i was originally going to use is going to be an extremely difficult and fiddle thing to slot in there. I'm going to try clipping down the lengths of the pre-soldered pins or even remove them entirely and solder directly onto the board itself. If that fails I may need to look at a smaller Arduino.

My circuit design is very basic. Effectively a battery connected to VIN and GND of the Arduino with an inline switch on the VIN so i can turn it on/off without disconnecting the battery. Then there's the other toggle switch which acts an an input (using 1 digital pin, 5v to the switch and ground). And the voltmeter output one connected to a PWM pin and to gnd.

There are smaller Arduinos than the nano. The Seeeduino is teeny tiny and would certainly fit. However, it can only take an input voltage of 3-7v which means a 9v battery is a no-no. I'm really really tight for space so I don't know if I can use another battery.


These cost £25 though so easily 4-5 times the cost of a Nano I'm not sure I want to sink that cash into this project.

If I do though I'll need to resolve the power situation.

Stacking 3 or 4 button batteries like LR44/AG13 would get me to 4.5 or 6v which might be enough. Capacity would be substantially less than a 9v but it's not a particularly taxing circuit and might still last plenty long enough for just the occasional demo, it's not like i'd be using this on a daily basis.

I did manage to cram in a Nano afterall. I cut off the pin headers and I’ll have to solder directly onto the nano but that’s ok. In hindsight I should have just bought a bare bones Nano that wasn’t presoldered with anything but nevermind.

The voltmeter finally fits in nicely with a hidden spacer at the very top. My first attempt at a screen graphic wasn’t quite right so it’s not shown here. The needle will also need painting white. To secure into position I’ll just glob a load of hot glue in there.

What was the mounting screws of the gauge nicely line up with the push button holes so I’ll shave those down so I can put some little switches on top. One will be the on/off button and the other will be the button that activates the jiggling needle part of the program.

The bottom “battery” cover is a little strange in that there’s less room than you might think. I now think that I’ll use two CR2032 batteries to generate 6v which I can feed to the Nano. The capacity of button cells isn’t great but it only needs to work for a few seconds at a time to demonstrate so battery life isn’t a huge concern.
Nighty80, simcarr liked this
It’s not a particularly complex shape once you’ve got the dimensions dialled in. I might whip something up in Tinkercad at some point. There’s a couple on Thingiverse already but they aren’t very good (no offence intended towards the creators, but they probably didn’t have access to the real device).

I took a break this weekend from this project to work on some other bits and pieces but will revisit this soon as I’d like to “tick” it off my todo list. Then I can release the instructions/code incase anyone else wants to try.
Small update; getting some latching (i.e. switches that when depressed stay on until pressed again) just ain't gonna fit with the larger voltmeter. And I'd rather have the larger voltmeter so need to rethink the functions. So... I'm not going to bother with an on/off switch at all. I'm just going to unscrew the bottom bolt to connect the battery and then screw it back together. It's not like I need it to be available all the time anyway. This also enables me to better replicate the real device functionality. That is that when 'Test' is pressed the needle goes straight to max, when released it goes back to 0. When the 'Read' button is pressed that's when the real device would give a reading in roentgen but I'm just going to make the needle twiddle back and forth between half way and the red zone.
Right I’ve been scratching my head trying to get this circuit working in reality using the voltmeter. I may/may not have damaged the resistor that it came with but in my experiments I ended up replacing it with just a 1k resistor. Sending the full analogWrite of 255 was overkill but 155 seems to take it to max without the needle flinging right off for the “Test” mode! I then chose a random range of 50-150 for the twitching “Read” mode.

You’ll have to excuse the messy looking breadboard, wiring spaghetti with alligator clips all over the place, the final version will be a lot neater, honest!


Just realise the 2 and 20 are having a hissy fit in the wrong place but I think im getting close now to a final screen design that fits with the voltmeter i have. I could have just digitally replicated the genuine screen but then the arc and stuff would be in the wrong place relative to the needle on the voltmeter im using.
simcarr, Dioxide liked this
Quick update. Still a final few tweaks needed to the screen design but fairly happy with it. Going to need copious amounts of glue to keep everything in place though as there’s a risk of moving it all when the buttons get pressed. We’ll see.
Nighty80 liked this
Screen isn’t dead-centre but I didn’t want to peel the sticker off and do it all again. It’s a really tight fit for all those spaghetti wires.
All connected to an arduino nano
Powered by four AG13 button batteries.

There’s no on/off switch sadly so I have to unscrew the bottom and slip a piece of cardboard between the batteries when I’m not using it.
RedSpecial, Nighty80 liked this
Lol its broken already, my fault. The glue I used on the buttons reacted with the rubber material and has basically broken the buttons. So at some point, I'm going to have to take it back apart again and solder some new buttons onto it. Whoopsie. Thankfully it's not too difficult a fix, albeit a pain in the bum.
I managed to "unstick" one of the buttons and in the serial monitor console I can see that the Arduino successfully detects a button press but the needle still doesn't move. I tested sending just an analogWrite to the needle and it moves fine so I can only assume it's something to do with the buttons being busted which is why nothing is happening. I don't have any more spares at the moment so I've ordered some more and I'll see what happens when I solder them back. Quite frustrating because I felt I was so close to completion.

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