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RC1 Real Time Clock

tebl·RC-ONE·RC1 Real Time Clock/RC1 Real Time Clock.kicad_pcb

RC1 Real Time Clock PCB layout, top view — open source board by tebl

About the RC1 Real Time Clock PCB

RC1 Real Time Clock is an open source PCB design by tebl, published on GitHub under the CERN-OHL-1.2 license. It is a 2-layer board measuring 99.1 × 59.7 mm, with 28 components from 18 distinct parts.

Other key parts include the 74LS04, DS12885, 74LS14, 74LS27 and 74LS138. By type, the board carries 8 capacitors, 6 ICs, 4 connectors, 3 diodes, 3 resistors and 2 jumpers.

It belongs with the retro computing and displays & leds designs in this gallery.

From the project

A recreation of the MOS KIM-1 microcomputer, the start of the Commodore-line of computers. Complete with hex keypad, six digit displays and a lot of 8-bit fun!

Wanted a Real Time Clock, but have been a hard time locating a suitable circuit for it since most of them either contain batteries that ran out a decade ago or are based on I2C or SPI (which I don't feel like bit-banging now or possibly ever). Appearantly there is a chip called DS12885 that is suitable and was readily used on the XT and AT line of computers, so they are cheap and plentiful though have a multi-plexed bus that is probably why it haven't been much used for SBC builds. Did however find an article in Elektor Electronics from april 1985 that uses it, so I've tried my best to adapt…

Main components on the RC1 Real Time Clock

74LS04DS1288574LS1474LS2774LS138

RC1 Real Time Clock bill of materials (BOM)

28 components, 18 distinct parts.

QtyPartRefs
1
74LS04
U1
1
DS12885
U2
1
74LS14
U3
1
74LS27
U4
2
74LS138
U5, U6
1
32.768kHz
Y1
1
Expansion
J1
1
ADDRESS
J2
1
SQW
J3
1
Battery
J4
1
RES_SEL
JP1
1
IRQ_EN
JP2
1
RAM_CLR
SW1
3
1n4148
D1, D2, D3
7
100nF
C1, C2, C3, C4, C5, C6, C7
1
10uF
C8
2
100k
R1, R2
1
150k
R3

RC1 Real Time Clock design files

The KiCad project lives in the tebl/RC-ONE repository on GitHub; these links point at the commit this page was built from.

RC1 Real Time Clock: common questions

How big is the RC1 Real Time Clock PCB?

The RC1 Real Time Clock measures 99.1 × 59.7 mm, has 2 copper layers and is 1.6 mm thick.

How many components are on the RC1 Real Time Clock?

28 components, from 18 distinct parts. The full bill of materials is listed on this page.

Where can I download the RC1 Real Time Clock design files?

From the tebl/RC-ONE repository on GitHub, which has the KiCad layout; the links under Design files point to each one.

Can I use the RC1 Real Time Clock design in my own project?

Yes, under the terms of its CERN-OHL-1.2 license, which tebl chose for the repository.

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