Braille Printer Photos A project from 1980 Part of the Braille Printer Web Pages by Douglas W. Jones THE UNIVERSITY OF IOWA Department of Computer Science These photos date from when I worked at the University of Illinois School of Basic Medical Sciences at Urbana

I took these photos in early 1980 during the assembly of the Braille printer. I scanned them in 2022 from 8 inch wide prints that had been stored in a manilla envelope for over 40 years.

Note that I took the photos during printer assembly, and none of them show the printer in its final working state. Photos showing the wiring include a small number of wiring errors that we fixed after the photos were taken, and other wiring and parts were not yet installed when I took the photos. None of the photos include the carriage motor, and none include the final platten assembly with its brass platten and toggle-jointed paper holddowns.

Numbers (such as 3.1.7.1) given with each figure reference the parts list making up section 3 of the text.

Parts mounted on the base plate (3.1)

The center rear of the printer includes barrier strips C and D, and the filter capacitor for the 24V DC supply. barrier strip A is at the top left of this photo, and the filter capacitors for the 8 and 16V supplies are on the left. The exhaust fan and heat sinks for the current limiters are on the right.

The empty space in the center left will be largely filled by the carriage motor, and the empty space at the lower right is where the circuit card will go.

The left rear of the printer includes barrier strips G and H as well as tie-point strips E, F and I. The capacitors have not yet been installed on top of strips E, F, H and I, so you can see the bridge rectifiers suspended between strips E and F.

The two big transformers on top are wired in parallel to provide the 24 volts at fairly high current needed by the carriage motor. The two smaller transformers provide logic power and the +/- 12V power needed by the single card computer.

At the bottom of the photo, in front of the motor mounting plate, you can see the microswitch used to sense the carriage home position and the loudspeaker used to indicate error conditions. These both sit under where the paper advance assembly will go.

Rear view of cabinet (3.1.2.1)

From the rear of the printer, air inlet on the right ventilates the power transformers, with the line fuse above and to the right of the inlet and the line cord below and to the left of the inlet. The DB-25 socket left of the inlet is the RS-232 port, while the exhaust fan is on the left of the photo.

The paper hold downs, visible from the rear on top of the printer did not work, so they were redesigned. The problem was that the tension on the paper required to pull embossed braille bumps out of the dies on the platten was enough to lift the hinged lids over the sprocket teeth.

Circuit Card Assembly (3.1.7)

The circuit card component side fully assembled onto the mounting bar, oriented so that it reads from left to right like the schematic diagram, but upside down. The voltage regulator for the 5V supply is on the left. This supplies both the chips on the board, the loudspeaker and the various switches that are inputs to the single card computer.

The rightmost transistors switch the power to the carriage motor windings. These high-current windings need fast rise time, ensured by the current limiters, and fast fall time, helped along by the 5-ohm power resistors on this board.

The notch in this circuit card clears the paper advance sprocket.

The circuit card wire side fully assembled onto the mounting bar, shows that the board is spliced because the available proto-boards were not big enough.

The photo also shows that the ground for the higher power circuits (solenoids and motors) has been carefully separated from the logic ground. These grounds were only connected at one point, on terminal strip I.

Carriage Installation (3.1.12.1)

The assembled and installed carriage rides on low-friction ball bushings on hardened shafts, pulled left and right by a tight loop of stainless steel wire wound around the drum of the carriage motor. Unfortunately, the motor is out of sight in this photo.

Barrier strip K under the carriage is linked by the loop of ribbon cable to barrier strip L on the side of the carriage. At the left end of its travel, the carriage closes the microswitch visible to the left.

Paper Advance Mechanism (3.2.1)

The assembled paper advance mechanism sits just above and behind the carriage. It is arranged to clear the top rear arms of the carriage end plates, while cut-outs in the carriage motor mountin plate clear the sprockets and paper advance motor.

Barrier strip J is close enough to the motor to be within easy reach of the pigtail leads of the motor wires and it supports wires just long enough to reach barrier strip D by the circuit card.

Computer Support Plate (3.4)

The assembled computer support plate serves as the lid of the printer case. It supports the Cromemco SCC (Single Card Computer) that controls the mechanism, the control switches and the power switch.

The 3 internal control switches are for options that the user is not expected to set, while the external switches and buttons are for user controls.

From the outside, the computer support plate and the paper-advance mechanism form a single smooth top, supporting the paper on the output side of the mechanism where it should be easy for a user to read (or feel) the embossed dots.

The controls to the left of the paper path include a big on-off switch, a small operating mode switch and two push buttons, one for linefeed (single line advance) and one for form feed (full page advance).

Some of those who looked at our prototype wondered why we didn't include any status LEDs. Visual indicators are of little use for a blind user, which is why we put a loudspeaker in the printer. We found ways to use the speaker to indicate a number of error conditions, including a horrible noise to mean "turn me off now" — on hearing this, nobody we tried it on needed to be told what to do.

The paper advance mechanism can be reconfigured for narrow (letter size) paper or wide (computer printer size) paper. Reconfiguration requires partial dissassembly of the paper advance mechanism, so it is not very convenient.

The photo shows the early hinged hold-downs for the paper over the sprockets. As already noted, this design did not work well and was replaced.