TTL Clock with 7447 7490 and 7400 IC's - Page 4 - Electronic Circuits Projects Diagrams Free

RODALCO · 17th March 2008, 04:53 AM

Some data from the TTL IC 7492 is attached.

Bear in mind that the 7492 only gives a BCD code off from 0 to 5.
(see truth table)

Source: ( Digitale Klokschakelingen, Herbert Bernstein )

Regards, Rodalco

Pete61 · 28th March 2008, 01:53 AM

Hi All,

I need help with designing a clock with old the 7400 series IC's. I have a 1 MHz crystal "can" oscillator (4-pin).
How can I use this to drive seconds, minutes and hours.
I have tried basic design but it is not working. HELP!!!!!!

RODALCO · 28th March 2008, 04:03 AM

Are you sure that your crystal is working ?

If yes, you have to divide the output it to get the 1 Hz frequency .

Inefficient but it works, is to divide it with 6 x 7490 IC's to 1 Hertz. It is probably easier to get a standard 3.2768 MHz crystal and divide it by 16.

To test your clock use the 50 Hz mains frequency double it via a bridge rectifier to 100 Hz via a small 5 or 6 Volts transformer.
Take off signal via a 1 K 0hm resistor ( I draw you a sketch later , teatime sorry ).

MRCecil · 28th March 2008, 05:49 AM

Quote:

Originally Posted by Pete61

Hi All,

I need help with designing a clock with old the 7400 series IC's. I have a 1 MHz crystal "can" oscillator (4-pin).
How can I use this to drive seconds, minutes and hours.
I have tried basic design but it is not working. HELP!!!!!!

Hi Pete,

You didn't say what Vcc was for your oscillator, but the attached ckt. will operate OK at both 3.3V and 5V. It's just three cascaded '390's configured for 100 division per with the output at 1 Hz at 50% duty cycle. It should fit the bill.

RODALCO · 28th March 2008, 08:06 AM

Here are the promised schematics.

One is how to make an oscillator with a 7400.
Others are for 50 and 100 Hz ripple to drive clock circuit instead of crystal.

Regards, Raymond

Pete61 · 12th April 2008, 11:59 PM

Thanks for the help but I still have a problem! The canned oscillator I am using will only drive 10 TTL Max. I got it to work the seconds, however, it will not clock minutes.

Is there any way to boost or amplify the crystal's output?

I am using the old 7400 series IC's. Would changing to 74HC work better?

audioguru · 13th April 2008, 12:11 AM

74xxx ICs have a max input current of 1.6mA. 10 have a lot of current.
74HCxxx ICs have no input current. But might not detect a high from a 74xxx.
A 74HCxxx can drive only 2 old 74xxx inputs.

cls_tec · 13th April 2008, 12:45 AM

I built the second "ones" hand of a 74LS90 clock.But it seems to be stuck.but if I remove power and plug back in , then it changes.Could somebody advise how to resolve this problem?

thanks

audioguru · 13th April 2008, 01:13 AM

All digital circuits need a circuit to reset them when the power is applied.

cls_tec · 13th April 2008, 02:16 PM

Let me go into more detail. I nuilt it from this page http://electronics.howstuffworks.com/digital-clock6.htm

My timebase is the 60Hz line from AC mains.I plugged power in, but the leds seems stuck, no counting.They just dont move.It seems like something the preventing the counter from counting.

Could somebody please advise on this problem , Thanks a lot.

cls_tec · 13th April 2008, 03:49 PM

never mind my above question, I decoupled all power leads with .1uF and rebuilt the whole thing.I connected leds to QABCD checking for binary out. So it works now . thanks.I still dont know whether It is working right , since I cant read binary!

RODALCO · 13th April 2008, 08:30 PM

Decoupling all IC's is a must with TTL. (0.1µF or 100nF ceramic)

The IC's draw small surges in the 5 volt supply during switching which may trigger an input of an other IC hence erratic readings.

As cls tec sais use 74LS90 IC's.

I'm not sure what pete61 means with the canned oscillator ?
The output from the crystal is normally going to the divider and that output normally only drives one TTL gate.

cls_tec · 14th April 2008, 01:57 AM

Hi again guys ,

Canned Oscillators are those square 4 pin metal can oscillators.

http://electronics.howstuffworks.com/digital-clock4.htm

Above is the link for the power supply/timebase I built.The only modification I made is using a 9V-0V-9V transformer and used one side(9V-0V).

So I built some counters to experiment and found that I had to use four decade counters to get it slow enough to get the 0-9 second side.Problem is I dont have enough chips to then get the minute and hour side.It seems like somehow using a 9-0-9 transformer caused the AC line frequency to increase(it should have been 60Hz and I should have to only use 2 chips in divide by 10 and 6 to get 1 Hz and then one more decade counter to get 0-9 second side)

Thanks again very much,very fun project.

Pete61 · 14th April 2008, 03:46 PM

The canned oscillator I am using will drive 10 TTL max (Load). It oscillates at 1 Mhz. I'm using 6 - 74160's to aquire my 1 hz timebase. 2 - 74160's for seconds, 2 - 74160's for minutes etc...

I got the seconds to work, but the minutes stay at zero.

Any Idea's?

Pete61 · 18th April 2008, 05:00 AM

Guess Not!

A can oscillator has four pins.

Thank you all anyway. I will continue experimenting.

The clock is an anniversary present for wife. I have until Aug 1st to complete it.

I'm sure I will will have it all figured out by then.

Thank you all again and take care.

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28th March 2008, 01:53 AM	(permalink)
Pete61	TTL Clock Hi All, I need help with designing a clock with old the 7400 series IC's. I have a 1 MHz crystal "can" oscillator (4-pin). How can I use this to drive seconds, minutes and hours. I have tried basic design but it is not working. HELP!!!!!!

28th March 2008, 04:03 AM	(permalink)
RODALCO	Are you sure that your crystal is working ? If yes, you have to divide the output it to get the 1 Hz frequency . Inefficient but it works, is to divide it with 6 x 7490 IC's to 1 Hertz. It is probably easier to get a standard 3.2768 MHz crystal and divide it by 16. To test your clock use the 50 Hz mains frequency double it via a bridge rectifier to 100 Hz via a small 5 or 6 Volts transformer. Take off signal via a 1 K 0hm resistor ( I draw you a sketch later , teatime sorry ). __________________ There are more ways to get to Rome. Electricity, Electric clocks, Meters and Trains are great.

12th April 2008, 11:59 PM	(permalink)
Pete61	Thanks for the help but I still have a problem! The canned oscillator I am using will only drive 10 TTL Max. I got it to work the seconds, however, it will not clock minutes. Is there any way to boost or amplify the crystal's output? I am using the old 7400 series IC's. Would changing to 74HC work better?

13th April 2008, 12:11 AM	(permalink)
audioguru	74xxx ICs have a max input current of 1.6mA. 10 have a lot of current. 74HCxxx ICs have no input current. But might not detect a high from a 74xxx. A 74HCxxx can drive only 2 old 74xxx inputs. __________________ Uncle $crooge

13th April 2008, 12:45 AM	(permalink)
cls_tec	Help with 74ls90 counter I built the second "ones" hand of a 74LS90 clock.But it seems to be stuck.but if I remove power and plug back in , then it changes.Could somebody advise how to resolve this problem? thanks

13th April 2008, 01:13 AM	(permalink)
audioguru	All digital circuits need a circuit to reset them when the power is applied. __________________ Uncle $crooge

13th April 2008, 02:16 PM	(permalink)
cls_tec	Let me go into more detail. I nuilt it from this page http://electronics.howstuffworks.com/digital-clock6.htm My timebase is the 60Hz line from AC mains.I plugged power in, but the leds seems stuck, no counting.They just dont move.It seems like something the preventing the counter from counting. Could somebody please advise on this problem , Thanks a lot.

13th April 2008, 03:49 PM	(permalink)
cls_tec	never mind my above question, I decoupled all power leads with .1uF and rebuilt the whole thing.I connected leds to QABCD checking for binary out. So it works now . thanks.I still dont know whether It is working right , since I cant read binary!

13th April 2008, 08:30 PM	(permalink)
RODALCO	Decoupling all IC's is a must with TTL. (0.1µF or 100nF ceramic) The IC's draw small surges in the 5 volt supply during switching which may trigger an input of an other IC hence erratic readings. As cls tec sais use 74LS90 IC's. I'm not sure what pete61 means with the canned oscillator ? The output from the crystal is normally going to the divider and that output normally only drives one TTL gate. __________________ There are more ways to get to Rome. Electricity, Electric clocks, Meters and Trains are great.

14th April 2008, 01:57 AM	(permalink)
cls_tec	Hi again guys , Canned Oscillators are those square 4 pin metal can oscillators. http://electronics.howstuffworks.com/digital-clock4.htm Above is the link for the power supply/timebase I built.The only modification I made is using a 9V-0V-9V transformer and used one side(9V-0V). So I built some counters to experiment and found that I had to use four decade counters to get it slow enough to get the 0-9 second side.Problem is I dont have enough chips to then get the minute and hour side.It seems like somehow using a 9-0-9 transformer caused the AC line frequency to increase(it should have been 60Hz and I should have to only use 2 chips in divide by 10 and 6 to get 1 Hz and then one more decade counter to get 0-9 second side) Thanks again very much,very fun project.

14th April 2008, 03:46 PM	(permalink)
Pete61	The canned oscillator I am using will drive 10 TTL max (Load). It oscillates at 1 Mhz. I'm using 6 - 74160's to aquire my 1 hz timebase. 2 - 74160's for seconds, 2 - 74160's for minutes etc... I got the seconds to work, but the minutes stay at zero. Any Idea's?

18th April 2008, 05:00 AM	(permalink)
Pete61	Guess Not! A can oscillator has four pins. Thank you all anyway. I will continue experimenting. The clock is an anniversary present for wife. I have until Aug 1st to complete it. I'm sure I will will have it all figured out by then. Thank you all again and take care.