Count Down Timer Problem (Again) - Electronic Circuits Projects Diagrams Free

GOkussj5okazu · 23rd June 2008, 11:23 PM

Ok, I've got a problem with this circuit again. A member on here helped me the first time I had a problem and it was solved, but now there's a new problem.

When I press the reload button that connects pin1 of IC5 to ground, it loads the input value of 60. However, instead of holding that value and counting down from 60, it imediately jumps to random numbers and then to either 99 or 88. From there the count down function doesn't work. HOWEVER, if the count down is initiated before the counter lands on 99 or 88, it will count down to 00 just fine like it's suppose to. Pressing the reload button to 60 causes it to jump randomly again. Any ideas?

Mikebits · 23rd June 2008, 11:40 PM

You might need to debounce your switch. First you get bounce when you press the switch, then more bounce when you move your finger off the switch.
Check this link, your best bet is the RC solution, the other is adding a chip.
http://www.ganssle.com/debouncing.pdf

GOkussj5okazu · 24th June 2008, 02:19 AM

Alright, I modified it as such. It still does it. That was,actually, my first thought, because I know the switching circuit is very sensitive. It seems that the two 74HC192's are having errors holding the input value of 60. When I press the reload switch, it loads the 60, but then it jumps to either 99 or 88, and it's always one or the other.

I have another circuit similiar to this, but it's input value is 32. Also, I modified the wiring on the first gate of the 74HC20. In my other circuit, pins 12 and 10 are each pulled high through a gate from 74HC14. Logically, I would think it could work either way. Am I wrong in the assumption? Could the way I have it wired now be causing a problem?

Mikebits · 24th June 2008, 02:38 AM

Your debounce circuit needs to be built as shown in the link I provided.

You can work out the RC values as shown in the equations, also in link.

Also, there is no need for the extra inverter.

MrDEB · 25th June 2008, 03:27 AM

Your sw1 is not debounced
Also your 4 leds in parelle need a resistor. As your schematic indicates the Leds are pulling 28 amps as simulated using TINA.
This alone would rattle the power supply and cause all kinds of weird happenings
A 150 ohm resistor should bring it down to 23ma.
I would opt for a 200 ohm = 17ma

blueroomelectronics · 25th June 2008, 06:03 AM

MrDEB is right, you need a current limiting resistor for each LED segment not one common one. 170 would be about right. You'll also need 0.1uf decoupling caps on every IC.

GOkussj5okazu · 26th June 2008, 04:31 AM

Alright, here's what I've got. I haven't made these adjustments yet, but I will if ya'll think they look about right.

Boncuk · 26th June 2008, 11:01 AM

Come on and give LEDs 1 through 4 also an individual current limiting resistor.
They like it.

MrDEB · 26th June 2008, 11:21 AM

If you use a 2 watt or even a 1 watt resistor you don't need more than 1.
did adding the resistor, adding a switch de bounce, adding caps to supply/ground help??

Boncuk · 26th June 2008, 11:04 PM

Quote:

Originally Posted by MrDEB

If you use a 2 watt or even a 1 watt resistor you don't need more than 1.

Yes, he can do that of course. With different foreward voltages of the LEDs he'll get nice looking uniform brightness of all four. They do have different UF.

Mikebits · 26th June 2008, 11:35 PM

Yes, your debounce looks correct. Just calc the right values. I don't think you need R5 anymore.

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23rd June 2008, 11:23 PM	(permalink)
GOkussj5okazu	Count Down Timer Problem (Again) Ok, I've got a problem with this circuit again. A member on here helped me the first time I had a problem and it was solved, but now there's a new problem. When I press the reload button that connects pin1 of IC5 to ground, it loads the input value of 60. However, instead of holding that value and counting down from 60, it imediately jumps to random numbers and then to either 99 or 88. From there the count down function doesn't work. HOWEVER, if the count down is initiated before the counter lands on 99 or 88, it will count down to 00 just fine like it's suppose to. Pressing the reload button to 60 causes it to jump randomly again. Any ideas?

23rd June 2008, 11:40 PM	(permalink)
Mikebits	You might need to debounce your switch. First you get bounce when you press the switch, then more bounce when you move your finger off the switch. Check this link, your best bet is the RC solution, the other is adding a chip. http://www.ganssle.com/debouncing.pdf

24th June 2008, 02:19 AM	(permalink)
GOkussj5okazu	Alright, I modified it as such. It still does it. That was,actually, my first thought, because I know the switching circuit is very sensitive. It seems that the two 74HC192's are having errors holding the input value of 60. When I press the reload switch, it loads the 60, but then it jumps to either 99 or 88, and it's always one or the other. I have another circuit similiar to this, but it's input value is 32. Also, I modified the wiring on the first gate of the 74HC20. In my other circuit, pins 12 and 10 are each pulled high through a gate from 74HC14. Logically, I would think it could work either way. Am I wrong in the assumption? Could the way I have it wired now be causing a problem?

24th June 2008, 02:38 AM	(permalink)
Mikebits	Your debounce circuit needs to be built as shown in the link I provided. You can work out the RC values as shown in the equations, also in link. Also, there is no need for the extra inverter.

25th June 2008, 03:27 AM	(permalink)
MrDEB	De bounce ALL switches Your sw1 is not debounced Also your 4 leds in parelle need a resistor. As your schematic indicates the Leds are pulling 28 amps as simulated using TINA. This alone would rattle the power supply and cause all kinds of weird happenings A 150 ohm resistor should bring it down to 23ma. I would opt for a 200 ohm = 17ma

25th June 2008, 06:03 AM	(permalink)
blueroomelectronics	MrDEB is right, you need a current limiting resistor for each LED segment not one common one. 170 would be about right. You'll also need 0.1uf decoupling caps on every IC. __________________ Bill Smart Kits build Smart People http://www.blueroomelectronics.com

26th June 2008, 04:31 AM	(permalink)
GOkussj5okazu	Alright, here's what I've got. I haven't made these adjustments yet, but I will if ya'll think they look about right. Last edited by GOkussj5okazu; 26th June 2008 at 04:32 AM.

26th June 2008, 11:01 AM	(permalink)
Boncuk	Come on and give LEDs 1 through 4 also an individual current limiting resistor. They like it.

26th June 2008, 11:21 AM	(permalink)
MrDEB	Why add more? If you use a 2 watt or even a 1 watt resistor you don't need more than 1. did adding the resistor, adding a switch de bounce, adding caps to supply/ground help??

26th June 2008, 11:35 PM	(permalink)
Mikebits	Yes, your debounce looks correct. Just calc the right values. I don't think you need R5 anymore.