My HC4017's arrive today. Should I go with 2N2222 BJT's or with 2N7000 MOSFET's? I'm going to use only two 4017's, the first directs the march, the second dictates which section marches.

Isn't only one LED going to be lit at a time? Then what are the transistors for? An output from a 74HC4017 can source 55mA which is enough to destroy itself, destroy an ordinary LED and destroy your vision. Use a current-limiting resistor instead of a transistor or Mosfet that need more resistors. Since your supply is only 5V then all 10 LEDs need only a single resistor, because the LEDs that are turned off get a reverse voltage of 5V which is their maximum allowed voltage.

 

I'm driving three stages (3 x 10) of LED's. The transistors are only to turn on a single stage at a time so I don't have lights all over the place. Q1, Q2 and Q3 provide ground each through a 330 Ω resistor. I'm not done yet with my drawing but here's a preliminary post so you can see how the transistors are controlled:

Darn it! Forgot to upload!

 

Here: [edited]

 

I see what you are doing.
But you have three serious errors because you did not read the datasheets.
1) VR1 must connect to 5V as shown on its datasheet not to the output of the 555.
2) The supply must have a supply bypass capacitor as mentioned in its datasheet mounted close to the 555 because the 555 causes a huge supply current draw each time it switches which will mess up the counters.
3) Many ordinary 555 ICs (old TTL) will not be able to drive the clock on the 74HC4017 (modern Cmos) because the datasheets show that the minimum output high of a 555 with a 5V supply is only 2.75V and the minimum clock input of a 74HCxxx is 3.5V when it has a 5V supply. Use a Cmos 555 (LMC555 or TLC555) instead.

 

Some comments.

I don't see anywhere on the HC4017 datasheet where it says the part can deliver 55 mA in normal operation. It's guaranteed to make around 5 mA. The output voltage will decrease about 0.5 V with 4 mA output current. This increases with increasing output current, but not linearly. The max rated output current per pin is 25 mA, source or sink.

You can shift the input transition levels lower by changing to the HCT version. This part will work with the standard TTL input range of Vlow below 0.8 V and Vhigh above 2.4 V. But the CMOS 555 is a better part in many areas, so changing to it rather than changing the 4017 is the better solution.

The 555 oscillator schematic has an error that is easy to resolve. Delete the connection to pin 7 (let pin 7 float), and it should work fine.

ak

 

I don't see anywhere on the HC4017 datasheet where it says the part can deliver 55 mA in normal operation.

I am posting some graphs I got from Texas Instruments.

You can shift the input transition levels lower by changing to the HCT version. This part will work with the standard TTL input range of Vlow below 0.8 V and Vhigh above 2.4 V.

I forgot about the "T" version because I have never seen one.

The 555 oscillator schematic has an error that is easy to resolve. Delete the connection to pin 7 (let pin 7 float), and it should work fine.

Then the extra resistor might mess up the timing.

 

1) VR1 must connect to 5V as shown on its datasheet not to the output of the 555.

Um - I copied this from AAC:

 

2) The supply must have a supply bypass capacitor as mentioned in its datasheet mounted close to the 555 because the 555 causes a huge supply current draw each time it switches which will mess up the counters.
3) Many ordinary 555 ICs (old TTL) will not be able to drive the clock on the 74HC4017 (modern Cmos) because the datasheets show that the minimum output high of a 555 with a 5V supply is only 2.75V and the minimum clock input of a 74HCxxx is 3.5V when it has a 5V supply. Use a Cmos 555 (LMC555 or TLC555) instead.

2), BYPASS? Please explain.
3) I'll look and see if I have any, but I don't think I do. How about running a pull-up transistor?

 

I don't see anywhere on the HC4017 datasheet where it says the part can deliver 55 mA in normal operation. It's guaranteed to make around 5 mA. The output voltage will decrease about 0.5 V with 4 mA output current. This increases with increasing output current, but not linearly. The max rated output current per pin is 25 mA, source or sink.

My LED's should only be drawing around 7 mA. Notice the resistor is just before the transistor, limiting the current of any single LED that will be lit at any given moment. And the 2N3904 appears to only be dropping about 22 µV from Collector to Emitter. The base of the transistor has its own resistor; a 1K Ω limiting the current to 5 mA. So I'm not pushing anything close to the limits. Let me know if you disagree; I'm not arguing the point I'm offering my thinking. If I'm wrong I'd appreciate being redirected in the correct direction.

By the way, my chips did not come in today. They were in Arizona this morning, so they should be in town tonight and at my door tomorrow.

As you can see by the title of this post, I don't do well understanding the data sheets. Some are clear enough, others are a bit more confusing because I'm not well versed in the language.

 

The only 555's I have are NE555P.

Here's the data sheet. Says it can source (@5V) 200 mA and is compatible with TTL devices.

http://www.ti.com/lit/ds/symlink/ne555.pdf

 

Um - I copied this from AAC: "ATTACH"

Yours is different since it has pin 7 connected between the two resistors.

BYPASS? Please explain.

The datasheet for the LM555 says, "Adequate power supply bypassing is necessary to protect associated circuitry. Minimum recommended is 0.1μF in parallel with 1μF electrolytic." Another manufacturer (Intersil) shows the very high current surge (400mA) produced by an ordinary 555 which is why it needs power supply bypassing. The capacitor provides power for the current surge so that the 74HC4017 ICs do not get messed up.

The base of the transistor has its own resistor; a 1K Ω limiting the current to 5 mA.

You said you want the collector current 7mA, then the base current should be no more than 7mA/10= 0.7mA then the base resistor should be (5V - 0.7V)/0.65mA= 6.2k ohms.

The only 555's I have are NE555P.
Here's the data sheet. Says it can source (@5V) 200 mA and is compatible with TTL devices.

It says the minimum output high is 2.75V for an NE555 which is too low because a 74HC4017 needs an input of at least 3.5V.
The 74HCxxx is not TTL, instead it is high speed, high current Cmos which is different.
I never mix TTL and Cmos, therefore I have never tried a pullup resistor at the output of an ordinary 555.

 

@Audioguru Thank you.

Right now I'm having trouble just making a 555 oscillate.

You said you want the collector current 7mA, then the base current should be no more than 7mA/10= 0.7mA then the base resistor should be (5V - 0.7V)/0.65mA= 6.2k ohms.

Will take that for what it is. Thanks.

Haven't gotten my HC4017's yet, so I can't blow any of them up (yet).

I guess I'm OK with theory, but when it comes to practical understanding - I have lots to learn.

 

Right now I'm having trouble just making a 555 oscillate.

I hope it is not a cheap Chinese fake from ebay.

 

I hope it is not a cheap Chinese fake from ebay.

No. Had pin 4 held low, not high. Oops! Stupid breadboard. HEY! It's not MY fault. I just wired the darn thing. One problem I'm having is the leads of my resistors are about as thin as a Gnat's whisker. Really makes poor contact with the cheap breadboard contacts.

People -=-=-=-=- don't cheap out. Get the good stuff. You'll be much happier.

Good night y'all. Going watch TV with the wife. "(

 

Here:

Put the current limiting resistors between the LED and the Collector of the Transistor.

No. Had pin 4 held low, not high. Oops! Stupid breadboard. HEY! It's not MY fault. I just wired the darn thing. One problem I'm having is the leads of my resistors are about as thin as a Gnat's whisker. Really makes poor contact with the cheap breadboard contacts.

People -=-=-=-=- don't cheap out. Get the good stuff. You'll be much happier.

Good night y'all. Going watch TV with the wife. "(

Watch the new episode of The Orville. Excellent topic - they visit a world with a pure democracy. Not overly “sci-fly”. My wife really likes the show.

 

You said you want the collector current 7mA, then the base current should be no more than 7mA/10= 0.7mA then the base resistor should be (5V - 0.7V)/0.65mA= 6.2k ohms.

For the standard 10% rule of thumb for hard saturation, the base current should be no *less* than 0.7 mA. More than that is perfectly fine up to the point that you might damage the transistor.

However, that rule of thumb dates back to the 60's, when transistors - especially small signal general purpose transistors - were not as good as they are today. For an application like this I've never had any hint of a problem with Ic/20 or Ic/30. A 10K base resistor would yield about 15:1 Ic/Ib, plenty good enough for hard saturation under such a light load.

ak

 

I am posting some graphs I got from Texas Instruments.

Interesting plots. The numbers I quoted also are from the TI datasheet.

ak

 

If a common 555 is not heavily loaded, 1 -2 mA, it will easily drive a 74HC4017 with Vdd of 5V. Surley my 1975 Archer 555 data sheet would not lead me astray.
I would keep R7, minimum 1k,; Set VR1 & R7 ( Post #63 ) to 0 & note how hot 555 gets.
At first glance , the present plan seems to screw up plans for a comet tail.
Timing values not given so suggest VR1 about 1 meg., C1, 1 to 5 uF, R7 10k.
74HC4017, no current limiting , white LED, max. current measured was 44 mA @ Vdd =5V.

 

Watch the new episode of The Orville.

Been streaming it. Catching up. Like it too.

At first glance , the present plan seems to screw up plans for a comet tail.

Would have been nice, but I've wandered away from that route. Simple enough is simple. This is, after all, a child's toy. And no, they won't be able to access any of the electronics, mechanism's or the marbles. So even the 18 month old can enjoy the action, noise and lights. After all, my WIFE says she enjoys what I've got built so far. And I confess, I like it too. Will probably build another machine in the near future. But mine might have open marbles with tracks, loops and other stuff. NOT for children that might put marbles in their mouths.

 

Been streaming it. Catching up. Like it too.

Would have been nice, but I've wandered away from that route. Simple enough is simple. This is, after all, a child's toy. And no, they won't be able to access any of the electronics, mechanism's or the marbles. So even the 18 month old can enjoy the action, noise and lights. After all, my WIFE says she enjoys what I've got built so far. And I confess, I like it too. Will probably build another machine in the near future. But mine might have open marbles with tracks, loops and other stuff. NOT for children that might put marbles in their mouths.

This was a toy my we had when I was a kid. I just bought one in mint condition at a garage sale for $2.

This is not mine but enjoy...