0 2026/chumpchump pcb
spending 6 hours soldering and pretending i am having fun. a 4-bit computer made from ttl logic chips.I thought I’d post this project that I did this year, making a 4-bit computer from TTL logic chips. It’s a reimplementation of the final project for the computer architecture elective at harker, based on the following paper:
- Feinberg, David. “A Simple and Affordable TTL Processor for the Classroom”. https://doi.org/10.1184/R1/6591362.
Table of contents
Schematic and PCB
First, I drew up a schematic in KiCAD and designed a PCB. You can download the project files here.
I honestly yolo’d this design for the PCB, and the wiring was mostly done greedily and by vibe. I actually had to restart doing the traces halfway through my first attempt since I did not know what I was doing. Anyways, I sent this 4-layer PCB off to JLC PCB for $48 and thankfully everything worked first try. Never punished.
Instruction Set & ROMs
| Instruction | op7 a2 | op6 a1 | op5 a0 | op4/sel | ALU | S3 c7 | S2 c6 | S1 c5 | S0 c4 | M c3 | Cn (=c4) | Acc c2 | RW c1 | PC c0 | hex |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| LOAD const | 0 | 0 | 0 | 0 | B | 1 | 0 | 1 | 0 | 1 | x | 0 | 1 | 0 | AA |
| LOAD it | 0 | 0 | 0 | 1 | B | 1 | 0 | 1 | 0 | 1 | x | 0 | 1 | 0 | AA |
| ADD const | 0 | 0 | 1 | 0 | A+B | 1 | 0 | 0 | 1 | 0 | 1 | 0 | 1 | 0 | 92 |
| ADD it | 0 | 0 | 1 | 1 | A+B | 1 | 0 | 0 | 1 | 0 | 1 | 0 | 1 | 0 | 92 |
| SUB const | 0 | 1 | 0 | 0 | A-B-1 | 0 | 1 | 1 | 0 | 0 | 0 | 0 | 1 | 0 | 62 |
| SUB it | 0 | 1 | 0 | 1 | A-B-1 | 0 | 1 | 1 | 0 | 0 | 0 | 0 | 1 | 0 | 62 |
| STORETO const | 0 | 1 | 1 | 0 | A | 1 | 1 | 1 | 1 | 1 | x | 1 | 0 | 0 | FC |
| STORETO it | 0 | 1 | 1 | 1 | A | 1 | 1 | 1 | 1 | 1 | x | 1 | 0 | 0 | FC |
| READ const | 1 | 0 | 0 | 0 | A | 1 | 1 | 1 | 1 | 1 | x | 1 | 1 | 0 | FE |
| READ it | 1 | 0 | 0 | 1 | A | 1 | 1 | 1 | 1 | 1 | x | 1 | 1 | 0 | FE |
| JMP const | 1 | 0 | 1 | 0 | Logic 1 | 1 | 1 | 0 | 0 | 1 | x | 1 | 1 | 1 | CF |
| JMP it | 1 | 0 | 1 | 1 | Logic 1 | 1 | 1 | 0 | 0 | 1 | x | 1 | 1 | 1 | CF |
| JEZ const | 1 | 1 | 0 | 0 | Not A | 0 | 0 | 0 | 0 | 1 | x | 1 | 1 | 1 | 0F |
| JEZ it | 1 | 1 | 0 | 1 | Not A | 0 | 0 | 0 | 0 | 1 | x | 1 | 1 | 1 | 0F |
And I loaded a program to print out the fibonacci numbers on the LEDS:
0 LOAD 1
1 STORETO 0 # ram location 0 holds f(n)
2 STORETO 1 # ram location 1 holds f(n-1)
3 READ 0
4 LOAD
5 READ 1
6 ADD
7 STORETO 1 # ram location 1 = f(n+1)
8 READ 0
9 ADD
10 STORETO 0 # ram location 0 = f(n)+f(n+1) = f(n+2)
11 JMP 3I used the same program and python script shown in the original chump post. Contents of the program rom (U6) and control rom (U7):1
$ hexdump -C ctrl_rom.bin
00000000 aa 92 62 fc fe cf 0f 55 55 55 55 55 55 55 55 55 |..b....UUUUUUUUU|
00000010 55 55 55 55 55 55 55 55 55 55 55 55 55 55 55 55 |UUUUUUUUUUUUUUUU|
*
00002000
$ hexdump -C program_rom.bin
00000000 01 60 61 80 10 81 30 61 80 30 60 a3 55 55 55 55 |.`a...0a.0`.UUUU|
00000010 55 55 55 55 55 55 55 55 55 55 55 55 55 55 55 55 |UUUUUUUUUUUUUUUU|
*
00002000I programmed the AT28C64B EEPROMs with a XGecu Pro T48 programmer, using the minipro software tool. This EEPROM programmer ended up being the most expensive part at around $70, even more so than shipping a custom PCB all the way from China.
Buying shit from Jameco
I actually messed up here a bit, as I did not assign the correct footprint to some of my parts. The push button is scuffed, as the legs did not fit through the holes on the PCB so I just tacked it on with balls of solder on the pads. Also, the single pole double throw switch was completely incorrect. For the switch, I had to solder in some header pins and just use some jumper wires to connect to the switch.
| Item Number | Manufacturer P/N | Description | Quantity | Total |
|---|---|---|---|---|
| 46973 | SN74LS181N | IC, 74LS181N, DIP-24, ARITHM. LOGIC UNIT/FUNCT GENERATOR (.600”W IC, 74LS181N,DI | 1 | $6.60 |
| 46931 | 74LS174 | IC, 74LS174N, DIP-16, HEX D-TYPE FLIP-FLOP W/CLEAR HEX D- TYPE FLIP-FLOP DIP- | 1 | $1.23 |
| 46818 | 74LS161 | IC, 74LS161N,DIP-16, 4BIT SYNCHRONOUS BINARY COUNTR 4- BIT SYNCHRONOUS BINARY | 1 | $1.00 |
| 46771 | 74LS157 | IC, 74LS157N, DIP-16, QUAD 2-TO-1 LINE DATA SELECTOR QUAD 2-TO-1 LINE DATA SE | 1 | $0.94 |
| 46640 | SN74LS14N | IC, 74LS14N, DIP-14, HEX SCHMITT-TRIGGER INVERTER HEX SCHMITT TRIGGER INVERTE | 1 | $0.66 |
| 46252 | SN74LS00N | IC, 74LS00, DIP-14, QUAD 2-INPUT POS. NAND GATE QUAD 2- INPUT POSITIVE NAND GAT | 1 | $0.71 |
| 126797 | LMC555CN | IC,LMC555CN (TLC555CP) CMOS TIMER, 8-PIN DIP IC TS555CN CMOS Single (555) Lo | 1 | $1.32 |
| 48004 | 74LS74 | IC, 74LS74N, DIP-14, DUAL D-TYPE FLIP-FLOP DUAL D-TYPE FLIP-FLOP DIP-14 | 1 | $0.56 |
| 46359 | 74LS06 | IC, 74LS06N, DIP-14, HEX INVERTER BUFFER/DRIVER HEX INVERTER BUFFER/DRIVER DIP | 1 | $0.85 |
| 74827 | AT28C64B-15P | IC, EEPROM, 28C64B-15,5V 8kx8,DIP-28,150ns IC, EEPROM,28C64B-15,5V 8kx8,DIP-28 | 2 | $10.74 |
| 661757 | CF1/2W103JRC | @RES,CF, 10K OHM, 1/2 WATT, 5%, (10 BAG) Resistor Carbon Film 10k Ohm 1/2 Watt | 10 | $0.95 |
| 691622 | CF1/4W155JRC | @RES,CF, 1.5M OHM, 1/4 WATT,5%, (10 BAG) Resistor Carbon Film 1.5M Ohm 1/4 Wa | 10 | $0.43 |
| 2237175 | RC1W330EJT | @RES,CF,330 OHM, 1 WATT, 5% (10 BAG) Resistor Carbon Film 330 Ohm 1 Watt 5% | 10 | $1.33 |
| 2237191 | CF1W102JRC | @RES,CF, 1K OHM, 1 WATT,5% (10 BAG) Resistor Carbon Film 1K Ohm 1 Watt 5% | 10 | $1.33 |
| 2237204 | RC1W2K20JT | @RES,CF,2.2K OHM,1 WATT,5% (10 BAG) Resistor Carbon Film 2.2K Ohm 1 Watt 5% | 10 | $1.33 |
| 333973 | UT1871-81-M1-R | @LED,RED, 643NM,T-1 3/4, 75MCD,2.2V,V/A30,(10) LED Red Diffused 5mm T1-3/4 6 | 10 | $1.43 |
| 2357287 | C320C104M5R5TA-JVP | @CAP,MONO CER, RAD, 0.1uF, 50V, 20%, X7R, R20XR104M05L1YS, (10) @CAP,MONO CER,RAD | 10 | $1.14 |
| 33662 | TAP105K035SCS | CAP, TANT, 1uF, 35V, 10%, 4.2Dx6Hx3LSmm 1 uF 35 Volt Tantalum Capacitor | 3 | $1.68 |
| 137673 | DC-470-2P-R | PLUG,DC PWR, FEM,2.1X5.5mm,SLDR LUG, PC MNT,RT/ANGLE14.5mm L Connector Power | 1 | $0.47 |
| 155249 | ADTS31NV -JVP | SW,PB,TACT, SPST, OFF-(ON), OFF-(ON)50mA@12VDC, BLK,KRS- 3550-BK-Black SPST Mom | 1 | $0.33 |
| 2314127 | EG218 | SWITCH, SLIDE, SPDT, ON-ON.5A@50VDC, 3PIN PCB, BRD BD.31x. 16x.39” SWITCH, SLIDE,S | 1 | $0.81 |
| 2288607 | PH1-36-UA | HEADER, STRAIGHT, MALE, 1RW, 36PIN,. 1”CTR, 025”PST,.23”, GOL DTAIL HEADER, MALE, 1 | 1 | $0.85 |
| 48557 | SN74S189N | IC,74S189N, STATIC RAM, 16x4, TTL, 16-PIN-DIP IC,745189 | 1 | $4.65 |
| 47669 | SN74LS377N | IC, 74LS377N, DIP-20, OCTAL D-TYPE FLIP-FLOP OCTAL D-TYPE FLIP-FLOP DIP-20 | 2 | $2.38 |
I also bought a 5V DC power brick with a barrel jack connector off Amazon.
Photos!
After acquiring everything, I proceeded to spend like 6 hours in Area01’s Dabble Lab hand soldering all the components into the board, pretending to have fun. Here are the fruits of my labor.
Ignore how dirty my PCB is, I did not clean the flux off after I soldered and now it’s disgusting.
There you go! For about $150, you too can make an awful 4-bit computer. This post should have everything you need to recreate this monstrosity if for some reason you wish to.
Footnotes
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🫴 six sevennnn 🫴 ↩