Mini Amiga A4000 (Pi 3b Emulated/3d Printed)

A While ago we (myself and my daughter) had found a 7 inch LCD screen in a field when we were out walking the dog. To cut a long story short we had originally picked it up to put it in the recycle bin but when we arrived at home, we decided we would try drying it out and see if we could get it working.

Being a bit of an amiga fan I have always wanted an a4000 but they were (and still are) unreasonably expensive so we decided to design and 3d print a miniature one including a replica mini 1084s colour monitor. Where ever possible we like to use recycled or reclaimed electronics and components, with this in mind we went through some old projects to re-use some parts. We had an old cardboard box mame arcade machine project that we had created, played with and then left laying around for sometime as we had, had our fun with it. During the course of time some components had been removed for other projects, however there was a Pi 3b+ still in the box with a 32 GB SDcard so we figured this would be a good starting point to create our own amiga 4000.

While looking for what other parts we could use from our salvage box we happened across a power supply from a broken XBOX one S which was 12v 10A which worked, this was more than ample power that we could use to power this whole project including the display and other auxiliaries.

Now we just required sound output, we had been given a pair of old computer speakers from a family member not too long ago, we had already "stolen" the transformer from the speakers to use in another project but this was not and issue as we could simply power them from the XBOX supply.

We also salvaged some old connectors from sources such as old pc usb ports and an old Composite-RCA to Scart connectors.

Supplies

Raspberry Pi and memory card(3b+ in this case)

a usb memory key/dongle

a screen

a barrel power jack/plug

a HDMI2AV converter depending on the screen

a PSU

some terminal blocks

a buck converter (depending on PSU, 12v-5v3a in this case)

some wires (preferably old recycled ones)

a couple of switches

(where-ever possible recycled) screws

A hot glue gun

some cable-ties/tie-wraps various sizes

either a TDA2822 (ans some components)/2 speakers or an old pair of computer speakers.

old/used PC usb add on ports

some RCA cables 1 that can be destroyed, to be used as a lead

3 Leds (choose your favourite colour or green and 2x green and 1x red for authenticity)

2 old SCART to RCA connectors (optional)

3 500 ohm resistors (or there about's, we used 1k just because its what we had in the drawer)

heat shrink or electricians tape

Hot glue gun (optional)

an arduino if you are recycling a display

amiga software/adf which you can get for free from abandonware sites such as myabandonware.com

amiga workbench roms to copy to the usb key/dongle

Step 1: Assessing What We Have and Need

Now we have to asses if anything else was required for this project, a major issue we had was we were using a 12v Power source however as we are sure most of you will be aware, a pi requires 5v, we do have a couple 7805 regulator I.C's in our component supplies but they are not very efficient and would probably not provide enough current required for the pi, as a DC to DC buck converter is relatively cheap and super efficient it makes sense to purchase a new one of these as the pi 3b+ requires a 2.5 amp supply we purchased a 3 amp buck so as to give us a little "wiggle room".

For power indicators etc we would require 3 leds and (we user 470khm) resistors again this would come from our pre owned kit.

We will require some PLA and then require to design an amiga look-a-like case.

Some self taping screws recovered from previous projects we have worked on.

finally we require a 3.5 mm jack to RCA VIDEO to connect the screen and audio from the pi.

(You will also need to acquire a copy of amiga roms and workbench adf images which we already own)

Step 2: Getting the Screen Functioning (tracing Power Feeds With Basic Reverse Engineering)

(please note some of the photos have been recreated for dramatic effect or because we had a memory card failure so we lost the first lot :) )

First of all we opened up the screen and found that part of the plug was broken, we found an earth test point which was basically a big silver square in near the middle of the board so we could track down the the earths on the plug, we used our multi meter in continuity mode to do this and basically touch every pin on the connector, if there is a connector mark the pin as a - ground. Next we need to track down a positive input, we looked closely at the components on the board near the connector, we discovered an SS24 Schottky diode and after a quick google we discover that its part of a power regulation circuit so we can be confident that what ever pin connects to the positive side (arrowed in pics) is the power in, we used our multimeter in continuity mode to find the pin that was connected to the SS24 anode. all that was left to do was attach a 12v supply and bingo we have power, mark the pin. We soldered our black wire to the ground test point and a red wire to the live pin marked this was now the power in connections.

Now to figure out (assuming by the type and age of the screen) the location of the the composite input, first we power the screen on and put our meter on volts and then connect the meter ground to ground and then we touch every other pin on the connector, if there are any Positive connections we mark them DO NOT USE this is to ensure any device we connect to discover the input does not get any back voltage.

We now need one of the RCA leads from our supplies (preferably yellow so we know its a composite signal or we mark accordingly) we cut the plug off one end and strip the wires and tin. We next connect the outer wire to one of the grounds that we traced on the connector earlier. Now we need something with a composite output to track down the correct connection (this is possible using an arduino) , its as simple as turning the screen and RCA source on then touching each pin on the screen connector and checking to see if anything is displayed on screen obviously avoiding any pins that you may have marked as live(DO NOT USE) or ground earlier.

when you discover the correct pin mark then solder the wire and remember to use heat shrink to cover up to prevent any short circuits.

We have a working screen put the screen back together with the RCA plug and newly attached power leads hanging from the case, either use correct coded colours. i,e red, black yellow or mark with tags to help keep track of the connections. Use the hot glue gut to make a strain reliever at the point where the leads leave the screen case.

Now to solder one of the led's (a 1084s usually come with a green LED) to add a resistor inline, the longest leg of led being positive, remembering to add heat shrink attach some wires which is then joined to new voltage input wire for the screen we created. this is now the voltage in and the led power indicator for the front of the 3d printed case which will eventually have a switch and a barrel socket attached for voltage input.

Step 3: Writing Amibian Image

We started by downloading balena etcher to "burn" the amiga emulator we would download to the memory card in the raspberry pi.

next we download amibian to install on to the sdcard using balena etcher by following the instructions in the link.

skip onto the next sections util the first time you boot the pi then return to this point for help with configuration.

The first time you boot the pi you will boot into uae4arm config menu, assuming you have a keyboard and mouse connected, type in raspc or rapsi-config and press return when the software opens press 1 and expand the file system on your memory card reboot the pi and when the menu appears press 4 to load midnight commander, this is where we copy the roms and any amiga adf files you may have. when you are presented with the dual windows, in the left windows use the arrow keys to select /.. and press return until you can see the /media folder, using the arrow keys navigate to the media folder and browse until you find your usb drive, now navigate to the right window by pressing tab key, browse to the amiga directory using the arrow keys and select by pressing return, you will be presented with some predefined uae directories copy any adf files into the floppies folder and and amiga kickroms into the kickstarts folder, to do this in the right window highlight the folder kickstarts with the arrow keys then press enter to enter and select the folder, press shift and tab together to jump back to the left window, navigate to the folder where your kickstart roms are stored use the arrow keys and the spacebar to highlight any files you would like to copy over then press F5 to copy them, follow the same procedure for any adf files (which go in the floppies folder) reboot the pi when finished copying.

Step 4: Designing the Cases and Printing

For this part i'm afraid i'm not skilled enough in fusion 360 to design an miniature case set so i had to use my usual design software to design the case with a pi 3b+ mount (please feel free to modify the case as required). I basically used primitive cubes and modified the meet the shape of the commodore 1084s and amiga A4000/040

Step 5: Audio

After connecting up and testing the amplifier and speakers we discovered the amplifier was broken but the speakers where working, we simple attached a set of wires to each speaker and used a AAA 1.2v battery to touch the wires on the contacts and listened carefully to see if we could hear a light popping sound coming from the speaker, if the sound was present we could be confident the speaker worked. To solve this problem of the non working amplifier we used a TDA2822 ithat we had in our components drawer. Following the instructions from the TDA2822 datasheet we built the basic amplifier circuit as recommended and installed this in the monitor with our speakers for sound.

Step 6: Assembly

Now we needed to strip down and use all the plugs and leads that we are using and then wire them and make the appropriate leads such as usb extension cables and RCA extensions for the rear of the screen and then mount them using tie wraps and a hot glue gun.

on the xbox PSU the grey wires are 12v+ and the black wires are ground, we next connect them to a terminal block and paint the terminal block red with nail varnish to highlight the live outputs of the psu. next we need to make a mains plug extension to plug into the XBOX PSU, masking sure the cable is NOT PLUGGED INTO THE MAINS feed the cable through gap in the rear panel of the case labeled AC in on the case,.put some large tie-wraps on the cable to act as a cable arrestor just in case the cable gets pulled allowing a little room for slippage plug the cable into the PSU and leave un plugged from the mains until finished.

Next is to mount everything inside in their respective places, this is something that will vary depending on the scavenged components used, where you will be able to mount them, however the 3d print includes points to pull tie-wraps through to mount most things, anything else a hot glue gun will suffice. You will have to make the necessary cable lengths to suite your needs.

To make external usb connections we basically found an old set of pc usb ports and 2 faulty usb cables, cut the micro usb ends off, we then simply joined the cables to the ports connecting the wires colour by colour, like for like.

We mounted the USB ports in the slot pre made in the amiga case for them. we made a slight oversight and had to cut the casing off the usb ports to allow the amiga case lid to close fully we then plugged them into the pi.

we essentially followed the same procedure as above but wiring RCA wires to the RCA sockets that we had reclaimed from old scart plug and made RCA extensions using a tie-wrap to mount the ports on the back of the amiga

the buck converter we purchased all ready has an micro usb cable connected so its just necessary to connect the respective power cables to the XBOX PSU terminals, then plug the micro usb into the pi, next connect up the hdmi to rca converter and hot glue the converter in place.

Next we used an old molinex socket, added a wire to the PSU 12V out so we could link an external power point for the monitor/screen thus allowing us to power everything from the amiga base by simply putting a molinex plug on one end of the cable and a barrel power plug on the other which will connect to the monitor.

Construct the monitor by first pushing the screen into its mount inside of the monitor case attaching the power wires to the jack plug and our wires to the other set of the RCA/audio plugs that we salvaged.

Use tie-wraps and hot glue to install all the components, leads and plugs to the screen and the base. there are screw holes included in the 3d model for self taping screws to ultimately join the case together.

Step 7: Conclusions and Hindsight

After running the system for a couple of weeks we noticed that it run rather hot at sustained full loads to remedy this we mounted a fan into the back of the case where the vents are located at the back of the case and made a "wind director" out of cardboard to aim the air movement at the pi which seemed to fix the cooling issue.

We also found that the amplifier would make fizzing and varying high pitched "weeeeee" noises when no sound was playing so we drilled a hole in the monitor case and added a switch to the power of the amplifier to be able to turn it off when not in use it has the added advantage of not using any unnecessary power (albeit not very much) when not in use.

Thing we would change :

Install the HDMI2AV converter in the monitor rather than the amiga case and use a hdmi out on the amiga case so its not tied to the little monitor or a monitor with a composite input, then put a switch on the monitor input to select between composite direct and HDMI2AV so the monitor would have a RCA and HDMI input making it useable by other more modern devices such as a mini amiga or mini64 as well as older hardware.

Use a better solution than the molinex connector for the power out from the base to the screen.