Urgent Help Please Circuit Design 555 Cd4017

[spec]

In the video of post 93, when you measured across the initial cap it was zero volts. That means that the battery must not have been conected?

 

[spec]

i have more of those 10uf's i can swap them out

Be worth a try

 

[eTech]

Hi

Here's another way to drive the LED's. You could use aULN2004A.
The LED's are set for 2v@20mA but each channel can drive up to 200mA.

 

[Keshin]

ok i just changed out the first cap from the battery and after i plugged it in i got a reading of 2.28v but it was going down.
as i removed the 0v wire from the board it was hot, i cannot visually see any shorts

your help has been absolutely incredible and i think a safe bet would be for me to buy new components and start over (ill just hook his name plate up as ON for now until i make a new unit)
however as this opens up more time frame for this i reckon maybe we could try one of your more advanced ways of doing it (if your up to the challenge of helping me haha)
also i still will buy the components and retackle the schematic you have done as i would like to get to your issue 4

 

[spec]

You must get this circuit working.

But as to the future sure, I will help. But the advanced chip that the other members mentioned would be the way to go. There are quite a few experts on ETO who know exactly what to do and have actually built circuits with them. If you do a search on ETO you will find stacks.

Before you hang up the soldering iron. Can you take out the counter chip completely and see if the timer starts working then.

 

[Keshin]

ok i have disconnected the 4017 from the 555 circuit
and am replacing both caps this time, can i replace one
with a 25v 10uf instead of the 16v 10uf

 

[spec]

yes 10uF 25V will be just fine. As general rule, the voltage rating of a cap is just a not-to-exceed figure. You can always use a higher voltage. Same with all components, transistors included.
Think about maximum RPM with a car engine.

 

[audioguru]

I love/hate the 555. What I cant understand is that there are much better timers, but they never caught on. The 555 wasn't supposed to go into production I understand- it was just a design execise at National- I think that is true.

Nope. The NE555, SA555 and SE555 were designed by Signetics. Signetics also designed good RF ICs and compander ICs the NE570, NE571 and NE572 and their SA and SE sisters. Philips saw that Signetics had great ICs so Philips bought Signetics in 1975. I have the Signetics databooks. Later, National and everyone else copied the 555. Signetics/Philips had a 555 in a 14 pins case.

 

[Keshin]

still no luck, this second 555 timer is out of my 1st attempt board, and the 555 it replaced was the new one i got today, my guess is they are both fried. both new caps are still reading in the 0.20 - 0.30 area,

 

[spec]

still no luck, this second 555 timer is out of my 1st attempt board, and the 555 it replaced was the new one i got today, my guess is they are both fried. both new caps are still reading in the 0.20 - 0.30 area,

How strange. There is something I am missing. Apart from the reset imput on a 555 chip they are pretty rugged. I woud love to get my hands on your board and the possibly blown chips to find out what is going on- I'm intregued and baffled especially as I have said before there is nothing to the circuit. I guess you are out of 555s now.

 

[Keshin]

i would say something went wrong in todays circuit with the new 555 and i probably ruined the 1st 555 when i was trying to do it myself haha, its okay its 3am sunday here now so monday morning i will go pick up some new 555's and some other components.
if you get bored or anything and feel like continuing to join in you could write me a list of components that i should get to do this over again or a better way? its up to you, don't want to bother you to much haha

 

[spec]

3am Hell

Get some sleep and you will have a fresh view in messing with electronics. Shame we didn't get your sequencer sorted; I was certain we would. There is something wrong that I am mising.
You will never bother me. Just ask all you want and I will be only be to happy to help if I can.

You are good to deal with because you take a positive view and give plenty of data feedback which is a great help.

Talk to you again

So long

spec

 

[KeepItSimpleStupid]

Hat to butt in:

My take:

Make the exact circuit 50% duty cycle oscillator here:**broken link removed** on a solderless breadboard.

Make sure you can count the pin numbers correctly.

You should be able to transfer this to a real PCB. Make the LED connection to pin #3 a jumper. You will need the pull-up in spec's circuit. The resistor from the output to ground.

==

The LED's you already have working, I suppose. A logic level on the transistor turns on the appropriate LED.

==

The CD4017 CAN get damaged IF input pins are not connected.

 

[spec]

R11 at 560 ohms drops a max of 5.2V or so for 9mA base drive. But you are asking for 14 x 0.03A (if LED Vf =3V), or 420mA. 9mA is not enough base drive. For full saturation switching you need 40mA or the transistors will overheat in their linear region.

Hi Mo,

Thanks for your observations. Of course, you are quite right about the LED drive current. The thing is there was just not much time and the component choice was limited to what Keshin had.

My calculations are bit different to yours. It is my understanding that the VF of a blue LED is around 3V4, so with 200 Ohm ballast resistor that would give maximum If of 6V-3V4/200= 2V6/200=13 mA per LED. As a LED bank comprises 14 individual LEDs and associated resistors that would give a total current for each LED bank nof 14*13= 182mA.

Taking saturation Hfe of 20, this gives a requirement of 9.1mA base current. So from (6V- 600mV)/Rb Ib you get, a max RB of 615 Ohms. 560Ohms seemed close enough. You need to take away the 400 Ohm buffered output impedance of the CD4017, so the resistor would really need to be 614-400= 214R. I just didn't want to chance such a low value though.

For simpler construction.I'd suggest a 12V supply , and string 3 LEDs together at a time (2 minimum) with a 200R resistor to make up the letters. That should make the wiring a lot simpler and cut the number of dropping resistors down significantly. Current loads drop by around 2/3rs toperhaps 120mA per transistor (12mA base drive) and R11 can then be (12-.65)/.012 or about 1K.

Afraid that is not an option: 6V specified

Given a free choice of components, I would have gone for a micro coupled to a MOSFET driver array, but then that would not be electronics.

 

[audioguru]

Each LED has a 200 ohm series resistor. The supply is actually 6.4V and the blue LEDs might be as low as 3.2V. Then the 200 ohm resistors will have 6.4V - 3.2V - 0.5V saturation= 2.7V across them and the current is only 2.7V/200 ohms= 13.5mA not 30mA.
Most little transistors have their max saturation voltage spec'd with the base current at 1/10th the collector current, not 1/20th. Then the base current is 18.9mA but a CD4017B with a 6.4V supply has a typical output current of only 7mA when it drops 3V which is not enough current. So the transistors might have a 1.5V saturation voltage loss and the LED current will be 10mA if you are lucky. The poor little transistors will be fairly hot.

 

[spec]

Each LED has a 200 ohm series resistor. The supply is actually 6.4V and the blue LEDs might be as low as 3.2V. Then the 200 ohm resistors will have 6.4V - 3.2V - 0.5V saturation= 2.7V across them and the current is only 2.7V/200 ohms= 13.5mA not 30mA.
Most little transistors have their max saturation voltage spec'd with the base current at 1/10th the collector current, not 1/20th. Then the base current is 18.9mA but a CD4017B with a 6.4V supply has a typical output current of only 7mA when it drops 3V which is not enough current. So the transistors might have a 1.5V saturation voltage loss and the LED current will be 10mA if you are lucky. The poor little transistors will be fairly hot.

Apart from assuming x20 sat Hfe I just said all that.

The trans would not fry. Transistors do not automatically die just because they are not in saturation. Even if you asume that the VCE is as high as 1V the dissipation would still only be 182 mW. Thinking about it, maybe I will put heaters on the transistors in case they get cold in the winter months.

 

[MrAl]

Hi again,

Hey i dont know if you guys are aware of this but on this site there is also a 'chat' room you can go to talk back and forth. That might help in troubleshooting too. Wishing you good luck with this project.

 

[spec]

Nope. The NE555, SA555 and SE555 were designed by Signetics. Signetics also designed good RF ICs and compander ICs the NE570, NE571 and NE572 and their SA and SE sisters. Philips saw that Signetics had great ICs so Philips bought Signetics in 1975. I have the Signetics databooks. Later, National and everyone else copied the 555. Signetics/Philips had a 555 in a 14 pins case.

Quite right ag- my bad

'The IC was designed in 1971 by Hans Camenzind under contract to Signetics, which was later acquired by Dutch company Philips Semiconductors (now NXP).'

'An amazing fact about the 555 is that a billion are made every year.'

https://en.wikipedia.org/wiki/555_timer_IC

 

[absf]

....

I have the same experience helping someone on the forum and it turn out to be a nightmare. I just wish the one I helped would send the problematic board to me and I can repair it in no time, rather than answering on the keyboard typing as I am a slow typist plus I have to check my grammar while I type.

May be the OP should have started on a breadboard. Make the circuit working first, then commit to a PCB. Or put sockets on the 2 chips.

I have checked the wiring and I see no mistakes on both sides but if there is any solder bridges or dry joints, it would be difficult to notice on the pictures.

Allen

 

[spec]

I have the same experience helping someone on the forum and it turn out to be a nightmare. I just wish the one I helped would send the problematic board to me and I can repair it in no time, rather than answering on the keyboard typing

Hello Allen,

yes that is exactly how I feel- so frustrating, and such a simple circuit too. As you say, just a few minutes hands-on and you would soon suss it.

I am a slow typist plus I have to check my grammar while I type.

Me too, but I have to check for spelling, sense, and gross errors in addition. Your grammer is pretty good.

May be the OP should have started on a breadboard. Make the circuit working first, then commit to a PCB. Or put sockets on the 2 chips.

Yes, sockets (turn-pin) would have helped a lot, but it was all done in a rush to meet the deadline

I have checked the wiring and I see no mistakes on both sides but if there is any solder bridges or dry joints, it would be difficult to notice on the pictures

Nice work. You must be very thorough and have a load of patience- all signs of a good engineer. I suspect that there was a couple of faults. I would love to get my hands on the board to find out what was going on.

Chuck