Why is this CD4001 so noisy ?

Thread Starter

DarthVolta

Joined Jan 27, 2015
521
I have a cd4001, on a new BB, running from the computer's 5V. I have 10k pullldown res's on the 2 input's I'm using, w/ switches, and a 1k and LED on that O/P and the other inputs are grounded, and I have a 22uF and 100nF next to the chip. And it still runs poorly, changing brigness a lot, turning off even. So I GNDed the other outputs, and still no luck. I can unhook it's GND, and it still keeps driving the output LED, just not as bright.

I shouldn't need an RF can just to use this, even if it's a cheap breadboard.
 

Alec_t

Joined Sep 17, 2013
12,009
Breadboards with straggly wires are notorious for picking up interference. Each wire acts as an antenna.
It's not good practice to ground the outputs of CMOS gates directly. That can stress the IC unnecessarily.
 

Tonyr1084

Joined Sep 24, 2015
5,868
A project I did a while back - - - I was getting some huge ringing from an output and couldn't figure out why. Till someone pointed out that I was using my scope probe at 1X. (or was it 10X) Whichever, I was introducing a ton of ringing by the short ground cable. When I set up the scope properly the ringing was just about completely gone. Said "Just About Completely Gone".

Check your probes and your setup.

And yes, I also agree that breadboards are notoriously noisy.
 

ebeowulf17

Joined Aug 12, 2014
3,275
I have a cd4001, on a new BB, running from the computer's 5V. I have 10k pullldown res's on the 2 input's I'm using, w/ switches, and a 1k and LED on that O/P and the other inputs are grounded, and I have a 22uF and 100nF next to the chip. And it still runs poorly, changing brigness a lot, turning off even. So I GNDed the other outputs, and still no luck. I can unhook it's GND, and it still keeps driving the output LED, just not as bright.

I shouldn't need an RF can just to use this, even if it's a cheap breadboard.
According to the datasheet, even asking 3mA from the output may be too much. Try increasing your LED resistor quite a bit, maybe 10k to start.

Screenshot_20200415-064159~2.png

Also, I don't know how well protected the outputs are, but the others are right that you definitely should not have been grounding the outputs directly. It may be possible that the chip is damaged now because you've shorted outputs to ground (unless those outputs have over current or thermal protections, which I'm not sure about.)
 

Audioguru again

Joined Oct 21, 2019
3,007
I agree that the IC might be damaged now. NEVER short the output of a Cmos gate to ground or to the positive supply. The unused inputs can be shorted to ground.
The datasheet shows that with a 5V supply, it can typically produce 2.5V at 3.2mA so without a current limiting resistor an LED will be dim and the output transistor in the IC dissipates only (5V - 2.5V) x 3.2mA= 8mW. The maximum allowed dissipation of an output transistor is 100mW so it is fine without a current-limiting resistor.

The Texas Instruments datasheet shows an output current of 18mA into a 2.5V LED when there is no current limiting resistor and the supply is 10V. Then the output transistor dissipates (10V - 2.5V) x 18mA= 135mW which exceeds the maximum allowed dissipation so a current limiting resistor or additional series LEDs must be used to share the heat.

I agree that a solderless breadboard is the worst way to connect electronic parts together. I have always used a compact layout soldered together on a stripboard. The parts and copper strips formed most of a pcb when a few short jumper wired were added.
 

KeithWalker

Joined Jul 10, 2017
1,691
I have a cd4001, on a new BB, running from the computer's 5V. I have 10k pullldown res's on the 2 input's I'm using, w/ switches, and a 1k and LED on that O/P and the other inputs are grounded,

First, the output:
The resistor and LED should be connected between the output and ground . Even then in the worst case, with a VCC of 5 volts it can only source 1.6 mA. At the best, 3 mA if you are lucky, as pointed out in the previous post.
Second, the inputs:
This device inputs are FETs with extremely high input impedance and are very susceptable to radiated noise. The wiring to the pull-down resistors and switches must be kept as short as possible. In this case, some of the picked up noise can be filtered out by connecting a 0.01uF capacitor from each input to ground.
Regards,
Keith
 

Thread Starter

DarthVolta

Joined Jan 27, 2015
521
Ok I didn't remember their current output/pin being so low. Yeah and I might have damaged the chip in the past too.

I did read in an article, that u could short the unused outputs to GND, but yeah if this thing isn't stable, and it does switch on an output, that's not good.
https://www.dummies.com/programming.../digital-electronics-4000-series-logic-gates/
The input pins of CMOS logic chips are notorious for picking up stray signals in the form of electrical noise. Although it isn’t necessary to do so in experimental breadboard circuits, in an actual circuit you should connect all unused input pins to the positive supply voltage or to ground. (You don’t have to connect the unused outputs to anything — just the inputs.)
It was too late last night, it doesn't say that u could do that.
 

ci139

Joined Jul 11, 2016
1,696
? how you drive your LED-s -- the upper shoulder for 4000 series is 10x poorer than the lower shoulder

for the CD4000 (although it "works" down to 3V) the Vcc is best to kept equal above the +6V --e.g.-- it's not too good to drive the LED-s with it powered by +5V

the 10kΩ pull-downs might be too big allowing the noise to sneak in - which i doubt would be the case powered from battery . . . . but if you have your circuit attached to the PC that is perhaps fed by UPS ← then such may introduce transients to your PC.GND that may cause the anomalous instability
 

Thread Starter

DarthVolta

Joined Jan 27, 2015
521
I'll try another 4001, and a battery. I had the LED sat on GND, and with all 60Hz mains near me, I remember why I didn't like these chips, that and the 50 million wires needed to do anything w/ logic chips.

Overall, I found a DIP-8 EEPROM that I want to play with, and I've never tried much with my digital stuff, so it's about time I try some, now that I have a big bag of 10k's, and lot's of nice cat5 wire for jumpers, and nice wire-strippers
 
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Thread Starter

DarthVolta

Joined Jan 27, 2015
521
My goal last
through the resistors or immediately ? explain
Directly, that doesn't make sense, except that lately, reading about Arduino, etc, and I'm used to thinking there's some enable pin. I know there's not on that CD chip, dam.

Yeah, that just kicked in LOL.
 

Audioguru again

Joined Oct 21, 2019
3,007
Your stereo will play 60Hz if you unplug an RCA cable from your CD player and put your finger on its end, Then you are an antenna that picks up the 60Hz from electrical wiring all around you. We can hear frequencies down to 20Hz but most speakers do not go that low. When you hear the 60Hz then think about sound that is one octave below it. 30Hz is one octave below 60Hz and some speakers can produce it.
 
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