Introduction

A fax sends a sheet of paper over a telephone wire. The sending machine reads the sheet line by line: a head with an eye moves across the sheet, and every dot — black or white — goes into the line as 1 or 0. In the same second the receiving machine puts that dot with its pen onto its own blank sheet. There is no memory for a whole page: a dot has come — a dot is drawn. In this kit you build two identical faxes, put them on one line and send a drawing from one to the other.

  • lesson 1 — the feed: two feed rollers, a belt between them and a right-angle drive from the motor;
  • lesson 2 — the sheet sensors: PAPER at the entry and ENDPAPER at the exit;
  • lesson 3 — the head: a carriage on a belt with a pen and a line sensor on it; the motors are stepper motors;
  • lesson 4 — the stepper motor driver: a CD4029 counter and a decoder on “AND” gates;
  • lesson 5 — a line: two CD4013 flip-flops take the carriage along the line and back home;
  • lesson 6 — the whole sheet: a CD4017 sequencer feeds the sheet after each line and ejects it at the end;
  • lesson 7 — the FAXBRD board and the second machine: the start bit, the first transmission;
  • lesson 8 — quality: from a 2.6 × 5.2 mm dot to 0.65 mm — the sensor spot, a reduction gear, half steps;
  • lesson 9 — both ways: a line there and a line back, a needle pen, the receiver timeout;
  • lesson 10 — A5 format: the machine finds out the sheet width by itself;
  • lesson 11 — one line for the two of them and a panel with lamps, as on a real fax.
One machine assembled on its base: the panel lamps and switches on the left, the mechanics in the middle — rollers, head, sensors, reduction gears, the sheet below; on the right the line key, the 60 Hz clock and the FAXBRD board.
One machine assembled on its base: the panel lamps and switches on the left, the mechanics in the middle — rollers, head, sensors, reduction gears, the sheet below; on the right the line key, the 60 Hz clock and the FAXBRD board.
sheet sensorsPAPER · ENDPAPER · INLINEboard FAXBRDdrivers · line · sheetmachine Bthe sameheadline sensor · pensteppersfeed · headpanelSTART · RECV · FINEDOTPENFA…FD · HA…HDthe lineThe 60 Hz clock is outside the board, on its CLK pin
One machine: the sensors tell the board where the sheet is; the line sensor on the head sees a dot, the pen puts a dot; the board steps the feed and head motors and sends dots to the line — or takes them from the line if the machine is receiving.

What you need

The chips are ready-made: the kit file fax-chips.json, imported into the library with one button. These are real Texas Instruments chips — CD4029, CD4069, CD4081, CD4013, CD4071, CD4072 and CD4017 — with the same pin names as in the datasheet. Here we do not build them, we use them: you place a chip and hang labels on its pins.

The mechanics — rollers, gears, belts, motors, limit switches and the slide — you place yourself from the tables, part by part: a fax is above all mechanics, and the lessons show why each part stands exactly where it does. The drawings to send are ready-made, the files fax-house-a4.json, fax-chip-a4.json and fax-house-a5.json: they load with the ⬆ button in the sheet panel. You can also draw your own — with the pen right on the sheet.

How much it is

One machine is 26 chips with 2,172 transistors inside. Two machines on a line are 52 chips and 4,344 transistors.

Mode

Build and check in Fast mode. In Real the mechanics slow down and the motors skip steps.

If something goes wrong

At the end of each lesson there is a paste (Cmd+I): it puts into a new project everything built in the lessons from the first up to that one. If something does not work, paste it next to yours and compare it with your build.