Acorn BBC Microcomputer

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BBC Microcomputer keyboard
Acorn BBC Microcomputer.jpg
Branding BBC
Manufacturer Wong's, SMK, Philips?
Keyswitches Futaba MR-6C series
SMK J-M0404 series
Philips keyswitch
Switch mount Plate mount
Keycaps Double-shot spherical
Interface Proprietary internal

The BBC Microcomputer System from Acorn Computers Ltd, commonly known as the BBC Micro or Beeb, was a series of 6502-based 8-bit microcomputers introduced in the United Kingdom in late 1981/early 1982.

Overview

Unusually for an 8-bit home computer, these computers used discrete mechanical switches, mounted in aluminium and steel plates. Switches were sourced from Futaba, Philips and SMK. The three different brands of switch used different keycap mounts and the keycaps are not interchangeable between keyboard types, except presumably the two SMK types.

Prior to the identification of the switches, the keyboards were classified by Chris Richardson of 8-Bit Software into four types,[1] which are not numbered in the order that they were introduced. All the variants were supplied with spherical double-shot keycaps in a curious combination of black (technically very dark brown), flame red for the function keys, and olive drab for the cursor keys. The differences between the variants are minor.

The keyboard is integrated into the computer; it is secured by two screws and nuts and is extremely easy to remove, after removing the four screws that retain the case lid. Unusually for a plate-mounted keyboard, it is the PCB and not the mounting plate that is screwed down. The keyboard has two cables that connect to the motherboard: one ribbon cable for the matrix, and the speaker cable, as the speaker is integrated into the keyboard. The keyboard also has capacity for fitting a ROM socket and a DIP switch bank for setting hardware configuration (prior to the introduction of battery-backed memory in the Master Series). The DIP switch block (when fitted, and typically it was not) appears to be wired directly into the keyboard matrix, with the intention that the switches be read just as if they were additional keys.

Keyboard types

Type 1

This is the original and most common keyboard type, with an aluminium plate and Futaba MR-6C series switches. This appears to have been manufactured from the 1981 to 1984. The OEM was Wong's. The keycaps were manufactured by Comptec; this is not only evident from the design, but Signature Plastics have confirmed that Wong's was a major customer.[2] "Keytop set 'Comtec'" [sic] (£20.83) and "Spacebar (Comtec)" (£0.66) are listed in a catalogue, but the specific keyboard for which it was intended is not given.[3]

Type 2

SMK J-M0404 series switches with angled keystems, mounted onto a steel plate. Known manufacturing dates are from 1984. The OEM was SMK, part number 401KBM-006-90RⒶ. The shift keys, space bar and possibly also tab use the brown and beige low-friction version of the switch.[1] These switches have been reported to be unreliable.[1] The keycaps were sourced from SMK, as they fit SMK's moulding style.

The return key uses a pair of low-force switches in tandem, connected together on the PCB.[4] These switches have the brown slider indicative of low friction switches, together with a beige base.

Type 3

Philips keyswitches[3] The mounting plate is aluminium. Also known to be manufactured in 1984. The PCB is not branded. The keycaps were supplied by Comptec.

Type 4

SMK J-M0404 series switches with upright keystems, on an aluminium plate. Also known to be manufactured in 1984. The OEM was Wong's. The keycaps were supplied by Comptec.

Later computers

The Acorn Electron and the original Master Series machines used Futaba low-profile linear switches. The Master Compact used conductive rubber domes over a PCB, and later Master 128s used Cherry MY switches.[1] The Futaba low-profile linear switch did not have anything close to the reliability level of the simplified linear model.

External links

References

  1. 1.0 1.1 1.2 1.3 8-Bit Software — See Their Insides
  2. Correspondence with Signature Plastics, 2015-10-02
  3. 3.0 3.1 BBC Micro Mailing List — Subject: Interesting DRAM catalogue
  4. Correspondence with Andrew from CJE Micro's, 2016-10-06