Gerty Part 5 – Finishing Off

<< Part 4

There are 2 fluorescent strip lights which are cast in resin and intended to be lit from behind by a row of 8 LEDs provided in the kit. I decided to try and create a more energy efficient light to prolong battery life. After a fair bit of experimentation and prototyping, I came up with the following solution:
What would be the clear section of the resin part was carefully removed using the milling machine.

A sliver of stripboard that was trimmed down to fit inside the resin part, whilst still having the remains of 2 copper strips running along its length. One of the copper strips was then cut in the middle of the board to electrically isolate one half of each end.
a thin piece of solid core wire was soldered onto each copper strip so that it protruded past the end of the stripboard.
Now for the really tricky part – a surface mount cool white LED (1206 size) was soldered onto the protruding wires at each end, about 5mm from the end of the board. The LEDs were arranged so that both cathodes were connected to the wires on the strip that runs the length of the board, and the anodes were connected to the wires on the 2 separated strips.
The LEDs were then carefully bent up so they faced inward to each other from the top side of the board.

A couple of pieces of clear acrylic rod were turned down on the lathe to about 5mm in diameter, and were gently sanded with 800 grit wet & dry. This will help diffuse the light that comes later.
Each piece of acrylic rod was trimmed in length so that they fitted exactly between the 2 LEDS once the stripboard was mounted inside the resin light unit. The ends of the rod were countersunk a little to help the LED sit as flush as possible with the end.

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Finally some 2mm wide end covers were cut from some 8mm styrene tube – first a 2mm ring was cut from the tube, then a near 180 degree segment was cut so that it sat neatly over the acrylic rod, whilst coveing up the LED and connecting wires. This took several attempts to get an exact fit.

3 wires are soldered to the bottom of the stripboard, one common connected to both cathodes, and one for each anode. These will be connected to the controller unit in due course.
Meanwhile all the major components were sprayed white, or dark gunmetal as appropriate. They were then given several coats of Johnson’s Wax (aka Future Floor Polish) to provide a glossy surface on which the many decals will be applied.
The 3 small “mechanical” looking inserts were base-coated in gunmetal and then had the detail accented with some light silver drybrushing. Some thin brass rod is supplied to provide extra detailing.


Decal application was relatively painless but time consuming due to the number required. I tackled this in several sessions to allow one set to adhere completely before applying more in the same area. Beforehand I tested a couple of scraps of the decal material with both Micro Set and Micro Sol setting solutions. Micro Sol was a bit too agressive and caused considerable wrinkling of the film, but Micro Set seemed to be ok. None of the decals need to go on curved surfaces or over uneven details, so you could probably get away without a setting solution at all. Although Steve provides 3 sets of decals to cover mistakes, I found them plenty strong enough and didn’t need any spares at all.

After they were all throughly dry, an overcoat of Testors Acryl Master clear matt was liberally applied to remove any remnants of the glossy Johnson’s coat.

One of the issues with this kit was always going to be how to display it. Gerty ferrys himself around the moonbase suspended from tracks in the celing. To have a ceiling, you also need a wall and a floor. Steve had an impressive section of corridor used to display his master at the UKGK Show last year, but it was huge! I’d never have space for something like that so decided to come up with a “bare minimum” version. The critical dimension was the space between shelves in my display cabinet, which is 17″. I made a basic gallows from 1″ wooden batten and a bit of MDF I had kicking around. This gives a scale room height of 8 feet which seems reasonable.
3 holes were drilled into the end of the batten in line with the 3 holes in the large flat plate in the kit – 2 of these are for threaded studding to hold the kit in place, and one is for the power leads to exit. The kit is supplied with studding but they were too short for my needs, so I found some longer M3 bolts and cut the heads off.

The gallows was then blocked out into a basic corridoor wall section using foam core and sheet styrene. Nothing fancy, just a basic “C” shape with a slot in the ceiling where Gerty would trundle along.

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The power wires connect through the support gantry to a battery box hitten in the top section of the base. 3 AA cells provide enough power for around 24h of continuous operation – certainly enough to cover a weekend show period.

After final assembly, some weathering was applied using Flory water soluble washes. A liberal coat of dark grey was applied and then wiped around to give the required overall dirty appearance. Then some rusty stains were added around the vent slots in the large grey unit on the right hand side, and around some of the other grey items. Finally a liberal amount of “coffee” was slopped and splashed around the cup holder on the left.

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A video of Gerty in action

Gerty is available direct from Steve Howarth through Etsy

Gerty Part 4 – Finalising the Electronics

<< Part 3

The original plan was to put together a PCB with a minimalist ATMEGA 328 circuit to ferry the images from the SD card to the display in an appropriate sequence, but after a bit of rooting around I found I could buy a complete Arduino Pro Mini clone from the far east (free shipping) for less than I could source the 328 MCU alone locally (with inevitable excessive shipping). So that’s what I did.
The new plan was to just connect the Pro Mini, SD and display with a rats-nest of wires but eventually I decided to put together a small motherboard that would house the Pro Mini and SD, and use a couple of JST PH connectors to wire up the display, and LEDS for the 2 “fluorescent” tube lights on the body, and for Gerty’s “eye”. These will be driven by additional I/O lines from the Pro Mini so that they can be controlled via the software rather than just being always on. This also allows the motherboard to be detached and removed from the body of the kit for software updates.

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Getting the Display board into the right place has been a bit of a challenge, and has involved the addition of plastic mounting runners and guiding tabs to hold it securely. The bottom of the LCD has to protrude at exactly the right angle so that it mates with the bezel precisely once the bezel is inserted in place. I intend to leave the two halves of the body unattached, and held in place just with a couple of small neodymium magnets. This means that the bezel cannot be permanently fixed to the body either since it spans both halves.
After much fiddling & tweaking & fiddling & swearing, I’ve eventually managed to get everything in and staying in the right place!

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Part 5 >>

Gerty Part 3 – A New Display

<< Part 2

Despite having good results with the OLED, it was just a bit too small – there was a 2-3mm border around the outside of the active area of the display that I just wasn’t happy with. A bit more poking about on the internet revealed a possible replacement – a 1.8″ 160×128 pixel LCD, which across the short side was almost exactly the right size for the width of Gerty’s screen. It didn’t matter that it was taller, because the way the screen is angled, the unused portion would stick up inside the body.

One was duly ordered and delivery awaited (deliveries from the far east seem to have got considerably longer in the last few months…)

When it finally arrived, there were a few issues to deal with:

  • The LCD is attached on each side with sticky foam strips to a breakout PCB which is a tad too big, but as the connector is at one end it was possible to very gently separate the display from the sticky strips so that it could be lifted up at an angle. The PCB will be mounted inside the body, with only the display itself sticking out into the bezel around the screen.
  • The glass of the display is encased in a thin plastic surround, and this is still marginally wider than the original resin bezel that comes with the kit. I had to make a whole new bezel and shade from plasticard that was 3mm wider – a lot of work for such a small gain, but the display now fits perfectly.

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  • The display extends up into the body far more than anticipated – I had to mill out quite a bit of resin to get it to sit high enough but again this was mainly due to the size of the breakout PCB.

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  • The breakout includes a SD card reader on the PCB, but for some reason every time data is read from the SD card, the display flickers. Using the original standalone microSD reader I bought, there was so such problem, so I’ll probably go with the that one.

The active area of the LCD that is visible in the bezel is 128 x 85 – a slight increase in resolution from the 96×64 of the OLED, but the OLED does not suffer the viewing angle issues that are inherent in LCDs. It’s aggrivated because I’m basically mounting the LCD upside down. Swings and roundabouts…

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>> Part 4

Gerty Part 2 – OLED Test

<< Part 1

The OLED display uses a serial interface (SPI) to the microcontroller, which basically means all the data is send along one wire, one byte at a time (with a couple more wires to control the flow of the data). This makes connections very simple, but this comes at the expense of speed of communication. The software library that was supplied with the display wraps up the control of the data lines so that it is also easy to send commands such as draw line or show bitmap without having to worry about how the data is actually sent between the MCU and the display.

Displaying a full screen 96×64 bitmap took nearly a second, and the image could be seen appearing down the screen. When Gerty is in his unhappy/concerned mood, the image alternates between two views, one looking left, one looking right. I wanted to be able to reproduce this on my version, but that was going to be impossible at that speed.

The display library code library is generic and flexible, but controls all of the actual data transfer itself. The Atmel MCU supports a “hardware” SPI mode which allows the MCU to take over the data transfer at a very low level and is about 5 times faster that doing it via software. It was relatively straightforward to modify the display library to use the hardware SPI mode which gave an immediate improvement to the speed the screen is drawn.

The MCU does not have much RAM (2k) and a single full screen image is 12,288 bytes in size (6144 pixels with 2 bytes of colour data per pixel). The MCU does have much more flash memory (32k) and the display library expects any bitmaps to be displayed to have been saved into the flash memory when the MCU is initially programmed. I wanted to be able to load an image on demand from the SD card and then display it, so another modification to the library was required. An additional function was added that would display a single pixel high bitmap from data held in RAM. It then became a case of loading each line of the bitmap from the SD, sending it to the display and then moving down to the next line, until all the bitmap had been transferred.

The end result of these modifications was the ability to show any image on the SD card on demand, almost instantaneously.

Part 3 >>

Gerty from “Moon”

One of the best films of 2009 was Duncan Jones’ debut Moon, not least because it featured some high quality physical model-work. I’ve already built the SRS kit of the Lunar Rover, but now a kit of Gerty the computer is also available from Steve Howarth, the model shop supervisor on the film, and builder of the original props!
This is a 1/6th scale exact replica and comes in 24 resin pieces, as well as some LED assemblies for the strip lights, Gerty’s eye and a backlight panel for the main screen. To complement this there is a selection emoticons colour printed on acetate to insert into the screen to bring Gerty to life. There is also some brass wire and foil for extra detailing, some printed Post-It notes as seen in the film and finally a comprehensive set of decals – of which there is 3 copies of each to cover any mistakes in application.
The resin is of good quality generally but there were quite a number of pinholes that needed filling, particularly on some of the edges. Filling is fairly straightforward but did take quite a while in the end to get them all. It’s sometimes easier to drill out a tiny bubble with a 1mm bit just so you’ve got something a bit larger to squish the putty into.
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It would normally be quite a straightforward build – fit of the parts is good and can be painted beforehand in most cases, but I decided to go a little bit further and try and replace the screen with a fully functional OLED one, driven by a microcontroller and able to show the full range of Gerty’s emoticons.
The kit screen is almost exactly the same side as a 0.96″ colour OLED device available from – the active area is just marginally smaller, but it’s good enough. The biggest problem is that it comes attached to a larger PCB containing the display controller which means it’s not going to be a drop-in solution and some surgery will be required to get it into place. I think I will need to completely remake the surround & shade from scratch to accommodate it, but this should be a relatively simple job in plasticard.
The display controller communicates over a serial interface which means it’s very simple to connect to a micro controller. It has a resolution of 96×64 pixels with a 65k colour depth – not huge but even at this size, the data for just one emoticon would nearly fill the available flash memory of the microcontroller. I want to have all 11 emoticons available, plus a “boot” screen so additional off-chip storage in the form of a micro-SD adapter is also required. Luckily this uses the same serial interface so again connectivity is kept simple.
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There’s plenty of room inside the main body behind the screen for all the electronics, but probably not the batteries too. This probably isn’t too much of a problem as Gerty is designed to be suspended from above, so will need some sort of corridor section to hold her (him?) anyway which will probably give ample battery storage space.

Part 2 >>