Imported from GitHub: skiselev/ttl-clock · commit 995f059 · license GPL-3.0

Description

74xx ICs Based Digital Clock

README

TTL Clock

74xx ICs Based Digital Clock

Introduction

I got a bit tired from soldering SMD components, writing firmware, (and also observing people building vintage-looking Nixie clocks using modern microcontrollers). And recently when cleaning my parts boxes I found several 74LS47 7-segment decoders, some 74LS90 decade counters, and MAN1A 7-segment displays. So I thought, why not to build a nice little clock using these components.

Assembly Instructions

Assembly Instructions

Design Overview

Please refer to the schematic file in the Design Files section below.

The clock uses a 32768 Hz quartz crystal (X1) and 74HC4060 counter/divider IC (U1) to generate 2 Hz signal. This signal is divided further by 2 using a part of 74LS90 counter (U6). The obtained 1 Hz signal is fed to two 74LS90 counters (U11 and U12) that count seconds. The seconds reset circuit implemented using two 74LS00 NAND gates (U4A and U4B). This circuit resets both seconds and tens of seconds counters when they reach "60" or when "SECONDS" switch (SW1) is pressed, allowing seconds adjustment.

The most significant bit of tens of seconds counter is fed to the minutes counter implemented using two 74LS90 counters (U13 and U14) through a multiplexer built from three 74LS00 NAND gates (U2C, U2D, U4D). The multiplexer selects between this "one pulse per minute" signal and the 2 Hz signal allowing setting up minutes. Two additional 74LS00 NAND gates (U2A and U2B) implement an RS flip-flop used to de-bounce "MINUTES" switch (SW2). The tens of the minutes 74LS90 counter (U14) is wired so that it resets itself when it reaches count of "6", so that minutes wrap around at "60".

Similarly to minutes, the most significant bit of tens of minutes is fed to the hours counter implemented using two 74LS90 counters (U15 and U16) through a multiplexer built from three 74LS00 NAND gates (U3C, U3D, U4C). The multiplexer selects between this "one pulse per hour" signal and the 2 Hz signal allowing setting up hours. Two additional 74LS00 NAND gates (U3A and U3B) implement an RS flip-flop used to de-bounce "HOURS" switch (SW3). Both hours counters are wired in such a way that they will reset themselves once they reach the count of "24".

Six 74LS47 7-segment decoders (U5 - U10) are used to decode the binary outputs of the counters and 7-segment displays (U17 - U19) display the result in human readable 24-hours time format.

Design Files

Schematic - Version 1.1

Board - Version 1.1

Bill of Materials

TTL Clock V1.1 project on Mouser.com - View and order all components except of the PCB.

TTL Clock Version 1.1 project on OSH Park - Order PCBs.

Component type	Reference	Description	Quantity	Possible sources and notes
PCB		TTL Clock V1.1 Printed Circuit Board	1	Order from OSH Park or another PCB manufacturer using provided KiCad or Gerber files
Stand		3D printed stand for the clock	1	(Optional) Print on a 3D printer using stand.stl. Thanks to Michael K. for designing this stand.
Screw		M3 x 6mm screw	2	(Optional)
Capacitor	C1 - C16	0.1uF, 50V, multilayer ceramic capacitor, axial	16	Mouser: 594-A104K15X7RF5UAA
Capacitor	C17	100uF, 25V, electrolytic capacitor, radial, 6.3 mm diameter	1	Mouser: 710-860040473003
Capacitor	C18	12pF, 50V, multilayer ceramic capacitor, 5.08 mm lead spacing	1	Mouser: 810-FK28C0G1H120J
Trimmer Capacitor	C19	5-30pF, trimmer capacitor, 5 mm lead spacing	1	Mouser: 659-GKG20015
LED	D1 - D4	3 mm LED, same color as U17 - U19	4	Mouser: 859-LTL-4221 (red, 623 nm) 859-LTL-4211 (red, 697 nm, 2.5 mcd), 859-LTL-4231 (green, 565 nm)
Connector	P1	DC Power Jack	1	Mouser: 806-KLDX-0202-A
Resistor	R1 - R5	4.7 kOhm, 1/4 W	5	Mouser: 588-OK4725E-R52, 603-MFR25SFRF52-4K7
Resistor	R6	330 kOhm, 1/4 W	1	Mouser: 588-OK3345E-R52
Resistor	R7	15 MOhm, 1/4 W	1	Mouser: 660-CF1/4C156J
Resistor Array	RR1 - RR6	470 Ohm, 8 isolated resistors, 16 pin DIP	6	Mouser: 652-4116R-1LF-470, 652-4116R-1-470, or 46 x 470 ohm discrete resistors
Switch	SW1 - SW3	SPDT momentary switch, Omron D2F	3	Mouser: 612-SS0750301F040P1A, 653-D2F-01L
Integrated Circuit	U1	14-stage binary counter with oscillator, 74HC4060	1	Mouser: 595-SN74HC4060N, 595-CD74HCT4060E, 595-CD74HC4060E
Integrated Circuit	U2 - U4	Quad 4-input NAND gate, 74LS00	3	Mouser: 595-SN74LS00N, 595-SN74LS00NE4
Integrated Circuit	U5 - U10	BCD to 7-segment decoder, 74LS47 or 74LS247	6	Mouser: 595-SN74LS47N, 595-SN74LS47NE4, 595-SN74LS247N, 595-SN74LS247NE4
Integrated Circuit	U11 - U16	Decade counter, 74LS90	6	Mouser: 595-SN74LS90N, 595-SN74LS90NE4
LED Display	U17 - U19	7-segment LED display, 2 digits, common anode	3	Mouser: 859-LTD-6910HR (red, 623 nm), 859-LTD-6410G (green, 569 nm)
Crystal Resonator	X1	32768 Hz, 12.5pF load capacitance, tuning fork	1	Mouser: 695-CFS-20632768EZBB, 815-AB26T-32.768KHZ
Power Supply		5 V, 550 mA	1	Mouser: 490-SWI3-5-N-P5 (US plug), 490-SWI3-5-E-P5 (EU plug)