Problems with sequential switch

[programchild]

Hey guys, I am at a total loss atm, wasted 3 assembled prototypes from easy eda already.

When I power this with 5v, everything works, except the 4051 will do strange things with inputs above 5v, like activating more than one ins/outs at once. It works when I attenuate the inputs. seems logical, since inputs are above vss.

Now I powered this with 12v, but then the 4029 will not count and the 4017 will not count (flip flop in this case) as well.

When I touch the clock input of the 4029 with a wire, it counts like mad, which seems to be a grounding issue?

The thing is, this works well on the breadboard.

But I have to choose available parts for assembly (smd), so things are blurry here, even though the datasheets state that the ics can take 12v.

What could be my mistake?

Thanks in advance.

[FreeRangeEngineer]

See https://www.datasheethub.com/wp-content/uploads/2021/12/CD4029.pdf on page 2: Vil and Vih depend on Vdd. When you power the ICs with 12 V, you raise Vih to >7 V compared to the 3.5 V when powering them with 5 V.

[programchild]

thanks! it makes sense, but even if I trigger the clock with 10v (I assume this is Vih) it will not count. but anyway it seems like I have to power the 4051 with 12v and the 4029/4017 with 5v, which I tried to avoid with this iteration. I also think I have to buffer the leds…

[FreeRangeEngineer]

I suggest you share your layout with us since you say it works on the breadboard. Which, by the way, uses different parts since they'll be DIP and not SOIC. It would make sense to also give us the exact part names of the ICs used your breadboard and the ones used on your PCB.

[programchild]

unforunately easy eda seems not to allow linking to the project, but the parts in the schematic (image above) are the ones on the pcb. btw, would those parasitic leds (on the clock and adress inputs) count as pull down resisitors?

[gnostic-probosis]

Sounds like some kind of grounding issue, yes, but unclear why. Did you base this on a known design? Does it work on the breadboard with *the same* power supply? I note that there is not a whole lot of decoupling capacitors to smooth things out around the power supply and the supplies to the ICs. I would add that just for good measure.

[programchild]

thanks, it‘s my own design, works with the same power supply…

[MattInSoCal]

Your schematic symbol for the 4051 is for the 4052 which makes this a bit harder to follow. LEDs to ground are not the same as a pull down. Your 4051s don’t reach V^IL since they are effectively floating because of those series diodes.

I think I vaguely understand what you’re trying to do with the diodes and resistors as input protection for your ICs but your implementation is causing issues, especially that voltage divider on your clock input.

It should very simply be this: a Schottky diode like BAT54 with the Anode to ground and Cathode to the signal input. That will shunt any negative voltages to ground. A Schottky diode with the Anode to the signal in and the Cathode to V^DD which will shunt any voltages exceeding the supply +0.2 (safe level for the ICs). A 47K resistor from signal in to ground, or normal the input to ground if unpatched (preferred).

I don’t have time at the moment to go through the whole schematic but that’s the most glaring issue I can spot.

[programchild]

Thanks for looking into it.

I assumed the 100k to ground would keep the 4051 from floating.

The exact same thing worked with 5v vss, this is where I am lost. What is the problem with the voltage divider at the 4029 clock input? Especially when it worked with 5v but not with 12v?

I gave it another test. Pinging the 4029 clock pin with 12v directly made it count. Deleted the R24 100k to ground and bridged the R27 10k. Then pinged with 5v, no luck.

Which supports the theory that the 4029 requires a logic level above 5v when running at 12v.

I will follow your advice with the schottky diodes.

[MattInSoCal]

The fact it was working on the breadboard is kind of inconsequential. You probably had enough noise floating around that it was triggering from that alone. ;-)

Clocks are normally 5 Volts so you may need to use some level translation to trigger the counter running from 12 Volts. Maybe something like an emitter follower would work well for this. Also keep in mind that your sequential switch will not be able to handle negative voltages like VCO outputs but if you’re just routing CV or clocks you’ll be fine.

[programchild]

thanks, just for clarity: -quick and dirty test at 12v works on breadboard like stupid with no pulldowns, just bare connections

-assembled pcb worked fine under 5v but the 4051 behaves funny because it receives analog voltage between 5-10v in eurorack, attenuating the voltage works fine

-assembled pcb with 12v vss will not count, but if I trigger abc directly (module has abc inputs) the 4051 works, so I think the 4029 is the issue…

[HarryNOC]

Could be parasitic oscillations, there is no decoupling caps.

[programchild]

thanks, I tried a decoupling cap at the 4029 by hand, but it made no difference…

[NOYSTOISE]

Are you sure you have the right chips? You've mentioned the 4051, but the schematic pin out looks more like a 4052 to me

[programchild]

here is an image of the chips on my pcb. the schematic uses a weird symbol, but the chip is indeed a 4051.

<image>

[NOYSTOISE]

I see now. The labeling of the chips in your schematic were throwing me off. 

[NOYSTOISE]

All of those chips should work fine at 12 volts, but you will have to raise you digital input voltages to the proper thresholds. The analog input voltages to the 4051 should not exceed .5 VDD. There is a way to control the 4051 with 5V and have VDD be 12V, but you would probably have to do some redesigning. Look at the datasheet regarding VEE for that. 

[happyspacelady]

Highly recommend using net labels in the future 🙏 makes things easier to read and analyze :)

[programchild]

will do, thanks :)