Can anyone help me in designing presettable digital timer using 74LS192?
I have known already its pins w/ their funtions.
But I really dont know how to make digital timer(minutes and seconds
only).
Will anyone post a schematic diagram of it?
The timer is complicated because for the seconds count it has to
rollover to 59 instead of 99 and the 74LS192 is difficult to work with
from that perspective, but the timing is easy at 1Hz. The trick is to
activate the 10's digit counter /LOAD when its /BORROW is low on the
rising edge of the 1's digit CTR CLK, and to maintain /LOAD active past
the 1's digit counter /BORROW rising edge which is used to clock it,
ensuring minimum /LOAD pulsewidths are met and the load operation is
clean. The LCE does this by waiting for the coincidence of 10's CTR
/BORROW and 1's CTR CLK high state, which means the CTR's are due to
transition out of the 00 state. It then activates the 10's CTR /LOAD so
that '5' propagates into the 10's digit, which causes 10's CTR /BORROW
into high state. The high state on 10's /BORROW enables the AND gate to
pass the high 1's CTR CLK. This forces the 1's CTR /BORROW into the high
state and decrements the 1's CTR simultaneously. The LCE sense 1's CTR
/BORROW high and removes the 10'S CTR /LOAD about three gate delays
later (NAND+OR+NAND in the LCE), ensuring that the positive going edge
on its CLK due to 1's /BORROW does not corrupt the '5' that has just
been /LOAD'ed. From this time on the CTR's operate as simple decade
counter cascade as the manufacturer intended until the next 00 state.
This operation is not required for the minutes counters. The minutes
10's CTR /BORROW low state indicates that the whole CTR group is in
state 00:00 and CLK is low, so it's time to STOP. This is done by using
10's minutes /BORROW to zero the seconds CLK input AND gate, stopping
the down count while the CLK is still in the low state. This situation
must be adjusted when you go to set the timer for another count because
the DOWN input must be high to enable the individual UP counts, hence
the other signals from the SSSE module. Just to give an idea of what
you're up against, I have included the schematic of presettable down
counter with range from 1 second to 99 minutes and 99 seconds. Press
START, it counts down, and then shuts off. To set it, press STOP/SET,
and then press the UP switches for each digit in the display. Press
START to begin the countdown. The timebase is a 32.768KHz oscillator
using the 74HCT4060 14-stage binary counter with oscillator section. It
is best to maintain consistency and use 74LS parts throughout. If you
want to time in 100th's of seconds, then the oscillator has to be
changed to a 200Hz frequency, remove the LCE from the SDC, make it
identical to the MDC in other words, the counters will roll over to 99,
and change the display colon to a decimal point.
View in a fixed-width font such as Courier.
..
.. COUNTDOWN TIMER
..
.. MINS SECS
.. ------------------------------------------
.. | ---- ---- ---- ---- |
.. | | | | | | | | | |
.. | | | | | O | | | | |
.. | ---- ---- ---- ---- |
.. | | | | | O | | | | |
.. | | | | | | | | | |
.. | ---- ---- ---- ---- |
.. ------------------------------------------
.. | | | |
.. /4 / 4 /4 /4
.. | | | |
.. \---------\----. \---------\----------,
.. | |
.. ,---------------------------------. |
.. | | | |
.. | .-------------------------------------------------,
.. | | | | | |
.. | | | | | |
.. | | ----MDC----- | | ----SDC----- | |
.. +------|-|CLR -----| | '--|CLR -----| | |
.. | | | BO10M|---. | BO10S|------+
.. --- .--|-|UP1M | | | .-------|UP1S | | |
.. /// | | | | | | | | | | |
.. |.-|-|UP10M | | | |.------|UP10S | | |
.. || | | | | | || | | | |
.. || '-|CLKM MIN1S|/| | || .-|CLKS SEC1S|/| |
.. || |--- | | | || | |--- | | |
.. || .-|CLK MIN10|/ | || .---|CLK SEC10|/ |
.. || | ------------ | || | | ------------ |
.. ||--- | || | | -----74LS00----- |
.. ||/// | || | | | | |
.. -SSE-- || | || | | | __ / |---'
.. | | || | || | | / |------o G2|
.. | ___| || | || | '--o G1| \__|---.
.. | CLK|--------------------------------' \__|-- |
.. | | || | || | | | |
.. | CLK|--------------------------------------| \ | | |
.. | ___| || | || |G3 o------| \ |
.. | SSR|-. || --TSE--- '------------|__/ | |G4 o--'
.. | | | || | | || | +----|__/ |
.. ------ | '--------|UPMIN1S | || | | |
.. | | | | || -----------------
.. | '-------|UPMIN10S| || |
.. | | | || |
.. | | UPSEC1S|------'| |
.. | | | | |
.. | |UPSEC10S|-------' |
.. | -------- |
.. '------------------------------------------'
..
..
..
..
.. ****************** LOGIC MODULES ******************************
..
..
..
..
..
..
..
.. (SSSE)
..
.. -----------------START/STOP/SET ELEMENT-----------------
.. | |
.. | VCC |
.. | | |
.. | +----------------------+ |
.. | | | |
.. | o o |
.. | -| STOP/SET -| START |
.. | o 74LS14 o 74LS14 |
.. | | |\ | |\ |
.. | +-[560]-+-| o-+ +-[560]-+-| o-+ |
.. | | +| |/ | | +| |/ | |
.. | [330] === | [330] === | |
.. | | 100u| | | 100u| | |
.. | +-------+ | +-------+ | |
.. | | | | | |
.. | --- | --- | |
.. | /// | /// | |
.. | | | |
.. | +--------------------------------------+ |
.. | | | |___
.. | | +--+----------------------------------|SSR
.. | | VCC | |
.. | | | | |
.. | | +--------|-------------------------+ |
.. | | | | | |
.. | | | | | |
.. | | | | | |
.. | | | -------------------74LS112-------------- |
.. | | | | | | | |
.. | | | | +--------+ +--------+ | |
.. | | | | | --- | | --- | | |
.. | | | | | PRE | | PRE | | |---
.. | | +--|-|J Q |---+ +--------|J Q |---|--|CLK
.. | | | | |-- | | | |-- | | |
.. | | +--|-|CK | | | +--|CK | | |
.. | | | | | FF1 | | | | | FF2 | | |
.. | | | | | - | | | | | - | | |
.. | | +--|-|K Q |-+ | | +-----|K Q |---|--|CLK
.. | | | | | --- | | | | | | | --- | | |
.. | | | | | CLR | | | | | | | CLR | | |
.. | | | | +--------+ | | | | | +--------+ | |
.. | | | | | | | | | | | | |
.. | | | ---------------------------------------- |
.. | | | | | | | | | | |
.. | | +--------|------------+--+ | | |
.. | | | | | | | |
.. | +------------+ +------------------+ |
.. | | | |
.. | | | |
.. | | | |
.. | ------------- | |
.. | +----| RESET | | |
.. | | | | | |
.. | ----- | 2HZ 0SC | | |
.. | 32.768K | 32.768KHZ | | |
.. | ----- | XYSTAL | | |
.. | | | | | |
.. | +----| Q14|--+ |
.. | | | |
.. | --74HCT4060-- |
.. | |
.. | |
.. | |
.. --------------------------------------------------------
..
..
.. (TSE)
..
.. ---------------------TIMER SET ELEMENT---------------
.. | VCC VCC |
.. | | | |
.. | | | |
.. | | | |
.. | o o |
.. | -| SWSEC1S -| SWSEC10S |
.. | o 74LS14 o 74LS14 |
.. | | |\ | |\ |
.. | +-[560]-+-| o---+ +-[560]-+-| o-----|UPSEC10
.. | | +| |/ | | +| |/ |
.. | [330] === | [330] === |
.. | | 100u| | | 100u| |
.. | +-------+ | +-------+ |
.. | | | | |
.. | --- | --- |
.. | /// | /// |
.. | +-------------------------------|UPSEC1S
.. | |
.. | |
.. | +-------------------------------|UPMIN1S
.. | | |
.. | | |
.. | VCC | VCC |
.. | | | | |
.. | | | | |
.. | | | | |
.. | o | o |
.. | -| SWMIN1S | -| SWMIN10S |
.. | o 74LS14 | o 74LS14 |
.. | | |\ | | |\ |
.. | +-[560]-+-| o---+ +-[560]-+-| o-----|UPMIN10
.. | | +| |/ | +| |/ |
.. | [330] === [330] === |
.. | | 100u| | 100u| |
.. | +-------+ +-------+ |
.. | | | |
.. | --- --- |
.. | /// /// |
.. -----------------------------------------------------
..
..
..
.. (SDC)
..
.. -----------------SECONDS DOWN COUNTER--------------
.. | |-----
.. | +-------------------------|BO10S
.. | | |
.. | +---------------------------------------------+ |
.. | | | | |
.. | | -----PDCE----- | ------LCE------ | |
.. | | | ---| | |--- ---- | | |
.. | | | BO1|-------|BO1 LOAD |--+ |
.. CLR|--|---|CLR | | | | |
.. | | | ----| | |---- | |
.. | | | BO10|---+---|BO10 | |
.. UP1S|--|---|UP1 | | | |
.. | | | | |--- | |
.. UP10S|- |---|UP10 | +---|CLK | |
.. | | | | | --------------- |
.. | | |---- | | |
.. | +---|LOAD 1S_DIGIT|-----------/4----------------|SEC1S
.. | | | | |
.. CLKS|------|DOWN 10S_DIGIT|-----------/4----------------|SEC10S
.. | -------------- | |
.. ---| | |
.. CLK|-------------------------+ |
.. ---------------------------------------------------
..
..
..
.. (MDC)
..
.. -----------------MINUTES DOWN COUNTER--------------
.. | |
.. | |
.. | VCC |
.. | | -----PDCE----- |
.. | | | ----| |
.. | | | BO1S| |
.. CLR|--|---|CLR | |
.. | | | -----| |-----
.. | | | BO10S|-----------------------------|BO10M
.. UP1M|--|---|UP1 | |
.. | | | | |
.. UP10M|--|---|UP10 | |
.. | | | | |
.. | | |---- | |
.. | +---|LOAD 1S_DIGIT|-----------/4----------------|MIN1S
.. | | | |
.. CLKM|------|DOWN 10S_DIGIT|-----------/4----------------|MIN10S
.. | -------------- |
.. | |
.. | |
.. ---------------------------------------------------
..
..
.. (PDCE)
..
.. --------------PRE-SETTABLE DOWN COUNT ELEMENT--------------
.. | |
.. | VCC---+----+----+-+-+-+--------------+----+---+ |
.. | | | | | | | | | | |
.. | +--------------------------+ | | | |
.. | | | | | | | | | | | | |
.. | | +----------------------------------------------------+ |
.. ---| | | | | | | | | | | | | | |
.. BO1|--+ | +----------------------------+ | | +-|-+---+ | |
.. | | | | | | | | | | | | | | | | | | |
.. ----| | | | +-------------+ | | +-------------+ --- | |
.. BO10|----+ | | |VCC A B C D| | | |VCC A B C D| /// | |
.. | | | | | | | | | | |
.. | | | | --| | | | --| | |
.. CLR|------+----|CLR BO|---+ +-|CLR BO|-----+ |
.. | | | __| | | __| |
.. | | | CO| | | CO| |
.. UP1|-----------|UP 74LS192 | | +-----|UP 74LS192 | |
.. | | | CTR1 | | | | CTR2 | |
.. | | | | | | | | |
.. DOWN|-----------|DOWN QA|\ +-------|DOWN QA|\ |
.. | | | | | | | | | |
.. | | | QB|\| | | QB|\| |
.. UP10|-----+ | |---- | | | |---- | | |
.. | | +--|LOAD QC|\| | +-|LOAD QC|\| |
.. ----| | | | | | | | | | |
.. LOAD|--+ | | QD|\| | | | QD|\| |
.. | | | |GND | | | | |GND | | |
.. | | | +- -----------+ | | | +-------------+ | |
.. | | | | | | | | | |
.. | | | --- | | | --- | |
.. | | | /// | | | /// | |
.. | | +---------------------|---+ | | |
.. | +------------------------|-------+ | |
.. | | | |
.. -----------------------------------------------------------
.. | |
.. /4 /4
.. | |
..
.. 1S_DIGIT 10S_DIGIT
..
..
..
..
.. (LCE)
..
.. -------------------LOAD CONTROL ELEMENT------------
.. | |
.. | +------------------------------------+ |
.. | | +--------------------------------+ | |
.. | | | | | |
.. | | | ----------74LS00--------- | | |
.. | +-----|--------+ +--------|--+ | |
.. | | | | __ | | __ | | |
.. | | | | / |-+ +-| \ | | |
.. | +-------|--o G3| |G1 o--|--+-|--+ |
.. | | | | | \__|-+ +-|__/ | | | | |
.. ---| | | | | | | | | | | |
.. BO1|-------------|--------+ +--------|--|-+ | |
.. | | | | | | | | | |
.. | | +-----|--------+ +--------|--+ | | |
.. | | | | __ | | __ | | | |
.. | | | | / |-+ +-| \ | | | |
.. | | +-----|--o G4| |G2 o--|----+ | |
.. | | | | | \__|-+ +-|__/ | | | |
.. ----| | | | | | | | | | |
.. BO10|---+---------|--------+ +--------|--+ | | |
.. | | | | | ------------------------- | | | |
.. ----| | | | | | | | |
.. LOAD|-----------------------------------------------+ |
.. | | | | | | | |
.. | | | | | -----------74LS32--------- | | |
.. | | | +----|---------+ +--------|-------+ |
.. | | | | | __ | | __ | | | | |
.. | | | | | / /-+ +-\ \ | | | | |
.. | | | +--|--< G7| |G5>--|--+ | | |
.. | | | | \ __\-+ +-/__/ | | | |
.. | | | | | | | | | |
.. | | +------|---------+ +--------|-+ | | |
.. | | | | | | | |
.. | +--------|---------+ +--------|----+ | |
.. | | __ | | __ | | | | |
.. | | / /-+ +-\ \ | | | | |
.. | +----|--< G8| |G6>--|-+ | | |
.. | | | \ __\-+ +-/__/ | | | |
.. | | | | | | | | |
.. | | +--|---------+ +--------|-+ | | |
.. | | | -------------------------- | | | |
.. | | +----------------------------------+ | |
.. | | | | |
.. | +---------------------------------------+ |
.. ---| | |
.. CLK|-----------------------------------------+ |
.. ---------------------------------------------------
..
*********************** END MODULES ****************************
PART NO QTY
74LS00 2
74LS14 1
74LS32 1
74LS112 1
74LS192 4
74HCT4060 1
100UF10WVDC 4
560R1/4w 4
330R1/4W 4
32.768KXSTL 1
SW MOMON 6
0.01UF50V 12
DISPLAY 1
22PF 2
I drew it up on the fly- was fun
