74xx ICs Based Digital Clock aka Das TTL-Grab Uhrwerk*

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.

* "TTL-Grab" in German literally means "TTL grave" - a board with TTL chips arranged in rows and columns, that looks kind of like a graveyard.

Design Overview

Please see the schematic file in the 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) and 7-segment displays (DIS1 - DIS6) are used to decode the binary outputs of the counters and display the result in human readable 24-hours time format.

Bill of Materials

Link to the project on Mouser.com - View and order all components except of PCB.

Link to the project on OSHPark.com - View and order PCB.

Component type	Reference	Description	Quantity	Possible sources and notes
PCB		74xx Clock V1.0 Printed Circuit Board	1	Order from OSH Park or your favorite PCB manufacturers using Gerber files provided below.
Stand		3D printed stand for the clock	1	(Optional) Print on a 3D printer using standforclock.stl file provided below. Thanks to Michael K. for designing this stand.
Capacitor	C1 - C16	0.1uF, 50V, multilayer ceramic capacitor, axial	16	Mouser: 594-A104K15X7RF5UAA
Capacitor	C17	100uF, 25V, electrolytic capacitor, radial, 5 mm diameter	1	Mouser: 647-UVY1E101MDD
Capacitor	C18	12pF, 50V, multilayer ceramic capacitor, 5.08 mm lead spacing	1	Mouser: 810-FK28C0G1H120J
Trimmer Capacitor	C19	5-20pF, trimmer capacitor, 5 mm lead spacing	1	Mouser: 659-GKG20015
LED	D1 - D4	5 mm or 3 mm LED, color matching to DIS1 - DIS6	4	Mouser: 859-LTL-4221 (red, 623 nm, 8.7 mcd) 859-LTL-4211 (red, 697 nm, 2.5 mcd), 859-LTL-4251N (yellow, 585 nm, 8.7 mcd)
LED Display	DIS1 - DIS6	7-segment LED display, 0.4", 14 pin DIP, common anode	6	Mouser: 859-LTS-4910AHR (red, 635 nm, 2.2 mcd), 859-LTS-4810AY (yellow, 585 nm, 2.2 mcd); 859-LTS-4710AP (red, 697 nm, 0.8 mcd), SA04-11EWA (red, 625 nm), SA04-11SRWA (red, 640 nm), SA04-11YWA (yellow, 588 nm), SA04-11GWA (green, 568 nm)
Connector	P1	DC Power Jack	1	Mouser: 806-KLDX-0202-A; Jameco 101178
Resistor	R1 - R5	4.7 kOhm, 1/4 W	5	Mouser: 291-4.7K-RC
Resistor	R6	330 kOhm, 1/4 W	1	Mouser: 291-330K-RC
Resistor	R7	15 MOhm, 1/4 W	1	Mouser: 660-CF1/4C156J
Resistor	R8 - R11	470 Ohm, 1/4 W	4	Mouser 291-470-RC; Jameco 690785
Resistor Array	RR1 - RR6	470 Ohm, 7 isolated resistors, 14 pin DIP	6	Mouser: 652-4114R-1LF-470 Or 42 discrete resistors (e.g. see R8-R11)
Switch	SW1 - SW3	SPDT momentary switch, Omron D2F	3	Mouser: 653-D2F-01, 653-D2F-01L, 653-D2F-01F
Integrated Circuit	U1	14-stage binary counter with oscillator, 74HC4060	1	Mouser: 595-CD74HCT4060E, 595-SN74HC4060N, 595-CD74HC4060E, 771-HCT4060N652, 771-74HC4060N
Integrated Circuit	U2 - U4	Quad 4-input NAND gate, 74LS00	3	Mouser: 595-SN74LS00N, 595-SN74LS00NE4, 595-SN74ALS00AN
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
Crystal Resonator	X1	32768 Hz, 12.5pF load capacitance, tuning fork	1	Mouser: 695-CFS206-327KEZB-U, 815-AB26T-32.768KHZ, 815-AB26TRQ-32.7-T