Minimig - How to build the thing

BOM

The bill-of-materials for both the rev1.0 and rev1.1 is available for download in the download section. The BOM is pretty generic so I have listed the critical parts in the table below with some more information and possible sources.

XC3S400-4PQ208The Spartan-3 FGPANuHorizons, Digikey (XC3S400-4PQ208C-ND)
SD_CARDMMC flash card push-push connectorFarnell (9186212)
DC_CON2.1mm DC power connector (DC10A)Farnell (224959, 10 per package)
3.5MM_CON_PCB3.5mm stereo jackFarnell (152204)
DSUBH_9Mserial and joystick connectorsFarnell (1099289)
PS2_CONPS2 keyboard/mouse connectorsFarnell (1200113)
SP3232EUCNSO16 3.3V/0.1uF RS232 transceiverI used this one from Sipex, Farnell (9386955) but any compatible 3.3V/0.1uF chip will do
MC68SEC000FU20processor, 10MHz or morecurrently available at Digikey (MC68SEC000AA16-ND)
M68AW512Msram, at least 70ns, 44-TSOPII suitable replacement at Digikey (706-1048-ND)
PIC18LF252I/SPmicrocontroller 3.3V DIP + socketDigikey, Farnell
LM1117MP-ADJadjustable power regulatorDigikey, Farnell(9778187)
LED0805red, green and blue 0805 ledsFarnell (8529884, 8529906, 8529949)
CT_100U/6.3VTantalum B-case, ESR=0.07OhmFarnell (1135233)

For all other parts:
All resistors are 0805 sized, 1% metal film types.
All ceramic capacitors with values 100nF and 10nF are 0805 sized, X7R types.
All ceramic capacitors with values 100pF, 47pF and 22pF are 0805 sized, NP0 types.
All electrolytic capacitors have a pitch of 2.54mm or 50mill.

PIC programming and Bootloader

The only part that needs programming is the PIC microcontroller. The FPGA is configured upon startup by the PIC. This means that you do not need any JTAG cables or special tools to program a Minimig. You only need a pre-programmed PIC18LF252 microcontroller. Programmers for PIC microcontrollers are cheap and widely available, both as diy projects or as commercial programmers. I use the PICkit-2 programmer.
The PIC ship itself is a DIL component that is plugged into a socket and not soldered in as in a in-ciruit-programming setup. This is for good reason; PIC controllers can only be bulk-erased when operated at 5V. The Minimig operates at 3.3V so you would never be able to completely "reset" the PIC when something went wrong during in-circuit programming. Thanks to the socket the PIC can always be taken out and inserted in a programmer for reprogramming when it is needed.
Although the PIC can be directly programmed with the necessary firmware, I strongly suggest the use of a bootloader. A bootlader makes it possible to reprogram the PIC through the serial port. To serial select jumper is designed to facilitate this. By setting the jumper to "MCU", a null-modem cable can be used to connect the Minimig to a PC. This way, new firmware can be downloaded without removing the PIC from the Minimig board. I use the Tiny PIC Bootloader by Claudiu Chiculita. This bootloader is easy to use and works reliably. Please follow the link on the links page to download the bootloader. When you use this bootloader (and you should!) program the file called "tinybld_18F252_20MHz.HEX" (inluded in the Tiny PIC Bootloader archive) into the PIC using a programmer. Then use the Tiny PIC Bootloader download tool to download the Minimig firmware into the PIC. This will make future updates much easier.

SMD soldering tips

Soldering SMD's by hand is not easy but with the proper tools and lots of patience very good results can be achieved. To properly solder SMD's by hand, you should have at least the following tools:
* Soldering iron (preferably temperature controller, about 320-350 degrees celcius) with a tip of 1-2mm.
* solder wire with built-in no-clean flux (resin), less than 1mm in diameter.
* no-clean flux dispenser (pen-style, syringe).
* Tweezers to hold the components in place during soldering.
* Magnifying glass.
* Flux remover.

Soldering 0805, small ic's, sot23 and other small components

Soldering these components is a 4-step process:
1) Hold your soldering iron in one hand and the solder in the other. Apply solder to one of the pads by first pressing the soldering tip to the pad (pre-heating the pad a little bit) for a second or so, then apply some solder to the junction of the soldering tip and the pad. If all is wel the solder will flow out to cover most of the pad. If the solder stays at one place on the pad or won't stick to the pad at all, check the tip temperature or pre-heat the pad a little longer. If that doesn't help, use a little bit of extra flux.
2) Hold your soldering iron in one hand and the tweezer in the other. Get the component between the tweezers and heat the solder on the (now pre-tinned) pad again using the soldering tip. Position the component and remove the soldering tip. The component is now fixed at one end to the PCB and can not be moved anymore. We can now solder all other pins in step 3.
3) Hold your soldering iron in one hand and the solder in the other. Now solder the other end of the component. Hold the soldering tip against the junction between the component and the pad. Wait a second or so and apply solder to the junction. The solder will flow easily and form a nice-looking joint. Do this for all remaining pads.
4) Although the component is now fixed completely to the PCB, the first joint (the one that was created in step 1 and 2 to "fix" the component) probably doesn't look that nice. It is therefore advisable to resolder that joint using the method described in step 3. This way, all joints will look perfect!

Soldering large ic's and quad flat packages

These components are best soldered using the so-called "drag soldering" technique. Follow this link for a good explanation and a video demonstration of this technique. Your PCB will probably look like a mess after soldering these components because of the flux that is needed. Techically, the flux does not need to be removed because "no-clean" flux will not corrode are damage your PCB. To make it look good however, use flux remover to clean up the PCB.

Building order

Although it is generally recommended to solder all difficult parts (like the FPGA, RAM chips and 68000) first, I would like to advise another order of building the Minimig. This alternative order of building will allow the builder to test a sub-section of the board before soldering the expensive components like the FPGA.
One of the most important parts of the board is the power supply system. So, we are going to build this part first by soldering the following components:

All 10nF capacitors:
C5,C6,C7,C8,C16,C18,C19,C21,C22,C25,C28,C29,C30,C35,C36,C39,C40,C43,C44,C46,C52 and C55.
All 100nF capacitors:
C3,C10,C11,C12,C13,C20,C23,C24,C26,C31,C32,C33,C34,C38,C41,C42,C45,C50,C53,C54 and C56 (note that C10,C11,C12 and C13 are not strictly part of the power supply system but it's better to solder them now than to forget them later).
All tantalum capcitors: (NOTE: the marker on tantalum capacitors indicate the POSITIVE terminal! Please observe correct polarity, tantalum capacitors WILL burn...)
C4,C17,C27 and C37.
Power regulators:
IC1,IC3 and IC4.
Resistors and leds:
R37,R38,R42,R14,R26,R28,R2 and D1.
Electrolytic capacitors and the power plug: (NOTE: the marker on electrolytic capacitors indicate the NEGATIVE terminal)
C14,C9 and J2 (C15 is better not placed at this stage, see below).

The reason for not placing C15 at this stage is that C15 can get in the way when soldering the FPGA. C15 is to provide enough capacitance as close as possible to regulators IC3 and IC4. C15 is not strictly necessary and can be left out during testing at this stage.
At this stage, the power supply can be tested. Double check if all components are soldered correctly (especially the capacitors!) and connect a 5V regulated power supply to J2. D1 should light up blue. Feel if any of the regulators don't get hot. If all is wel proceed by testing the following voltages:

TestpointVoltage
Voltage at J6, pin 7+5V +/-5%
Voltage at J10, pin 7+5V +/-5%
Voltage at J5, pin 4+5V +/-5%
Voltage at J8, pin 4+5V +/-5%
Voltage at tab of regulator IC1+3.2V to +3.4V
Voltage at tab of regulator IC3+1.20 to +1.26V
Voltage at tab of regulator IC4+2.40 to +2.6V


Only if all of these voltages check alright you can proceed by soldering the big chips IC5, IC6, IC7 and IC9. Because all SMD parts at the bottom side of the PCB are now soldered, you cannot lay the board flat anymore. Therefore, give the PCB some "feet" before soldering the big chips. After that solder the remaining SMD parts and finally solder all trough-hole components. The PCB is now done!

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