CMOS 4017 Decade counter, can I sync and source the same output?

[Dead Crow]

Hi I have only recently read about sync and sourcing. I have made a simple circuit which uses a NE555 timer and a 4017 Decade counter to simply, as each output comes on it turns on a LED then as it goes off the next starts etc. I was just wondering if i can use the outputs when they are low to switch on other LEDs by supplying VS to the LED (obviously in the opposite direction as the LED which comes on when the output is high) AM I BEING DUMB?

[SgtWookie]

OK, it's "sinking" current and "sourcing" current.

Yes, you could do that. Keep in mind that you'll get the 4017 mighty toasty if you're sinking current from a bunch of LEDs. It's best if you keep the current per output under 4mA.

[Bill_Marsden]

Actually I've used it with 10ma for literally decades on the same part, but it is outside the specs. There has been some debate as to the actual spec, but as I interpret the data sheet it is 6.8ma. I wouldn't push this part too hard though, else Wookie's interpretation becomes prophecy.

A general rule of thumb within electronics is to keep it 50% of rated capacity, but if the circuit is not too important (just playing around) you can step out of bounds a little, as long as you're not going to freak if/when it blows.

Have you read this?

LEDs, 555s, Flashers, and Light Chasers

[SgtWookie]

It's commonplace for hobbyists fiddling around with things like solar robotics and other 'bots to abuse IC's far beyond their specified design limits.

One big objection is that if you load 4000 series CMOS logic IC's too heavily, you are in the "forbidden zone" - neither a logic 1 nor zero. This fact has wreaked havoc on many "n00b" projects. A n00b might assume that you can both operate an LED and output a logic level from a 4000 series CMOS, and then become disillusioned when it fails to work.

While one might get away with doing such things with some manufacturer's IC's, it is not a very good idea to do such things continually, and expect to always get away with it. Frequently, you will find yourself letting the magic smoke out of parts, even if you think are operating them within their specifications - at room temperature.

The trouble is, parts don't stay at room temperature. When parts heat up, their limitations change. If you're operating well out of specifications at higher temperature, things "go south" in a hurry.

My point is that this forum is primarily oriented towards the budding electronics hobbyist, who has an interest in electronics, but has limited knowledge of it. It's important that their projects be successful, as that brings a feeling of accomplishment, and that satisfaction will lead to future projects.

Encouraging enthusiasts to stay well within all specifications of components, will help a great deal to ensure that their future projects will have a high probability of success.

After all, if builders built buildings the same way that programmers wrote programs, the first woodpecker that came along would destroy civilization.

In a small, one-off single IC circuit, it really does not matter that much if it breaks - unless it's your first circuit. The idea is to teach people how to make reliable "building blocks" - so that they can assemble them into larger systems that will function reliably.

Remember the Eniac? The first general purpose computer? It broke several times a day in the first few years.
http://en.wikipedia.org/wiki/ENIAC
Of course, that's more dealing with the level of complexity coupled with the MTBF's of the day (Mean Time Between Failures), but such lessons learned should not be forgotten.

[Dead Crow]

thanks for that , sinking and sourcing, haha. I was wondering as i typed it. I will use transistors to power the leds, I need to get the right transistors the last i tried burnt out. I have some info of how to properly select them and will try expand my knowledge. The sinking and sourcing capability has really excited me to the artistic doors opened in making a really nice display eg. A bunch of bi-colour LEDs which are red when sinking and turn green when sourcing creating a green LED running through a red carpet sort of look. .. Thanks again, and its true what you say about sticking to the specifications I lost interest in electronics for a while because I tried to do things differently and it didnt work. cheers

[Bill_Marsden]

You miss a key point though, the circuit I've built has lasted 30 years, more than long enough to prove the basic concept. I always add the proviso about design, but it is possible to go to the other extreme and overcomplicate something.

If it works, use it.

To the OP, show us what you did (schematic). Odds are it is a simple fix. Wookie and I may disagree about minor issues, but overall we both get along pretty well, and both of us are very active here.

[Dead Crow]

hey thanks , i will upload the circuit soon

[Dead Crow]

Hi , I used a 2n3904 transistor to bring on multiple LEDs on the 4017 output with a 10K resistor in series to limit the base current. Unfortunately I didnt work out which to use ,I just copied someone elses circuit (It may have been Bills) . Looking at a datasheet I have discovered the PNP equivalent is a 2N3906 so Im going to try that out to sink bi-coloured LEDs red and source the same LEDs green when the output switches on. I surf and I cant wait to get a good wave effect going. Sorry I have not yet uploaded the circuit I will soon as possible, the problem is that the program I use is autocad and not everyone would be able to see it, but i may print and scan it at work as obviously the idea is, to share circuits.My girlfriend will never understand my obsession with LEDs

[SgtWookie]

Try bringing your AutoCad schematic up on the screen, size it to fill the screen, and then press Ctrl+PrintScreen or Alt+PrintScreen to capture the image of your screen in a buffer.

Then start MS Paint, and select Edit->Paste (or press Ctrl+V) to put the image into Paint.

Save it in .png format, as that format works great for line-drawing type images, is very compact, and it is not "lossy" like .jpg format is.

Then attach it using the "Go Advanced", "Manage Attachments" feature.

[Dead Crow]

Hi its in Jpeg format, only saw Sergeant's advice now, I will try that with autocad in future. Pls excuse the rest of the circuit missing and the untidy work I was in a rush to just upload something! Ok Im not sure if I need a 10kohm resistor for the PNP transistor but I will try it out. I couldnt design a way to sink and source the same output for a Bi-colour LED without using two transistors because the cathode of the LED is common to both colours. Im sure theres a way to do it with gates... but I have never used one sooo...transistors cost about 80 south african cents .... Please advise me, I have never used a PNP transistor... Im just using the same principles as I use with the NPN type. Cheers! hope the jpeg is readable