555 timer pulses in audio signal

[greysun]

Hi everyone!

For my latest project, I'm converting an old enclosure that was drilled for a battery to one that has the foot switch down at the bottom. I retrofitted the old hole with a jewel lens and a 555 timer LED circuit with 2 LEDs flashing (think old pinball or carnival display).

https://youtube.com/shorts/k1Dx8S_cJPE?feature=share

The problem: I can hear the timer pulses in the audio signal.

My assumption is that possibly a cap at the power source might help (or maybe even at the ground), but I have no idea how to think of values and all that...

The timer circuit is below (I'll admit it's a bit sloppy - definitely would make changes next time, but trying to work with what I've got here) - 9v is directly to the power supply, ground is to the LED lug of the typical 3pdt foot switch.






I could always just throw a standard LED in there, but I'm trying to have a little fun here, hehe... each pin with any power has 100u cap on it, and the rest are 1k resistors (I have so many, so I just ran them in parallel to get the values I wanted).

Any thoughts?

[jwin615]

Hey, you did it!
Try adding a .1uf ceramic cap parallel to the electro on the VCC pin.
You could also try a CMOS 555, as it won't have the current spikes of a ne555, but you'll likely need to tweak the RC filter some.

[greysun]

Hey, you did it!
Try adding a .1uf ceramic cap parallel to the electro on the VCC pin.
You could also try a CMOS 555, as it won't have the current spikes of a ne555, but you'll likely need to tweak the RC filter some.

I'll give the cap in parallel a try - I disconnected the timer board entirely to try and breadboard a few scenarios - including decoupling caps, setting the power supply same as a standalone pedal (5817 > 100u > 100n) and nothing even phased the pulse, so for now I just threw a red LED into it, which is still kinda cool.

the 555 chips were cheap, and I ordered so many thinking I'd be using 2 in each circuit for a 3-way flash, but alas... I simplified to 2 colors, so I'll stick with what I have to not be wasteful... BUT, I have a 2nd identical pedal to modify, so I'll give this a shot in that one and retrofit this pedal if it works... more to follow for sure.

This pedal is cool - I modded a mudbunny in Mayo specs with some varied part replacements and a switchable mids pot, but it never fit right in the enclosure, so I took out the 25kb pot, I used a 50kb with a 100k resistor in parallel (don't care about the taper, honestly) to get to 33k on the dot (a 4k7 sits between lugs one and 2), which is the exact value for R18 - all the way down is stock, turn it and you've got mids control. This left yet another drill hole to fill, so I guess more LEDs equals more better, hehe...

Thanks for the help - if you (or anyone else) thinks of anything else, my eyes/ears are open. :-)

[jwin615]

Another alternative is instead of an astable vibrator, use it as a hysteric oscillator. See attached. Not sure if it would improve or not but easy enough to breadboard.
Noise is likely from the current spikes from the NE555 because, for a brief moment both transistor are high. I didn't even consider this 2hen I made the original recommendation. My apologies. This isn't the case with a CMOS 555(LMC555) and they're almost as cheap as NE555. About $1.50 each.  Or you can get 10 for about $4 on AliExpress. Tayda doesn't carry them unfortunately. They can't handle as much current as the NEs, but 2 LEDs would be fine.
You could always use your spare NE555s and make some Atari punk consoles. Or a stun gun... Then you'll really be down the rabbit hole.

[greysun]

Another alternative is instead of an astable vibrator, use it as a hysteric oscillator. See attached. Not sure if it would improve or not but easy enough to breadboard.
Noise is likely from the current spikes from the NE555 because, for a brief moment both transistor are high. I didn't even consider this 2hen I made the original recommendation. My apologies. This isn't the case with a CMOS 555(LMC555) and they're almost as cheap as NE555. About $1.50 each.  Or you can get 10 for about $4 on AliExpress. Tayda doesn't carry them unfortunately. They can't handle as much current as the NEs, but 2 LEDs would be fine.
You could always use your spare NE555s and make some Atari punk consoles. Or a stun gun... Then you'll really be down the rabbit hole.

It's no worry, man... I like to experiment with simple-on-the-surface stuff like this, hehe. I'll breadboard up what you posted and try it... Worst case scenario, it just has an extra LED and I give the timers to my circuit bending buddy. I'd be out a few bucks tops.

It's still looks fun with the jewel lens either way - my goal has always been to make them look like toys - fun color enclosures, LEDs and knobs, no labels (though I think I may hit up a buddy with a cricut soon for a couple of the more complicated ones).

[jwin615]

If you BB it, try it with and without the .1uf ceramic in parallel as discussed earlier.
Out of curiosity, what is the circuit of the pedal you tried it in?
Also, I'd probably add CLRs on to the posted schematic then tune the RC to taste from there.
But add a single LMC555 to your next mouser/digi order before scrapping anything for good. I do think that would at least improve, if not fix it.

[greysun]

If you BB it, try it with and without the .1uf ceramic in parallel as discussed earlier.
Out of curiosity, what is the circuit of the pedal you tried it in?
Also, I'd probably add CLRs on to the posted schematic then tune the RC to taste from there.
But add a single LMC555 to your next mouser/digi order before scrapping anything for good. I do think that would at least improve, if not fix it.

Not sure I have any .1u ceramics - plenty of box, and one giant film... not sure if it'll make a difference, but I'll try out what I've got. I didn't think it would make a difference which 555 timer chip I got (I'll be honest in that I figured it was just a brand thing with the letters, LOL - even after all these years, still such a noob).

The circuit is a mudbunny from 2012 or 2013. I had a feeling this could happen, honestly, but like I said: I like to experiment a touch - I think I had an issue with a delay or tremolo on a one-spot a while back that was powering my whole chain when the muff was on; the immediate fix there was a decoupling cap on whichever pedal that was at the power supply, and the longterm was moving from the one spot (I have a MXR thing now, which I like - the one spot plug cracked the last time I went to plug it in. No thanks). It was too long ago for me to recall exactly (I think it was possibly a modulator on a 1776 multiplex?), and I think I rebuilt the pedal later on into a new enclosure anyway.

Either way, noted on the lmc - next time I order, I'll see... I have 5 of these little boards, and 3 or 4 other pedal enclosures to update, so may as well use em!

[jwin615]

TLC555CP at small bear is 70 cents btw

[greysun]

Just tried the .1u cap trick you mentioned - didn't work... still hear the pulses.

So I tried to breadboard the schematic above. Couldn't get it to flash, so I went to the internet to find similar schematics. Tried it a couple ways - I can't get the LED to flash at all using the above schematic - just kinda slowly turns off and never back on again. Thought it might be the chip, so I threw it into my working circuit to test and it worked fine.

Might have to table this for now... I'll get it eventually, but it seems like I might need some new parts and some time to breadboard some other options... at least the footswitch is where it should be and the jewel lens doesn't look too insane, hehe.

[greysun]

I did find this thread below, so it looks like I have a couple routes to try out here - seems like either the cap needs to connect up with LED, or I need to add in a cap/diode combo... will experiment maybe this weekend, but for now - just trying to get my rig dialed in. :-) More to follow...

https://www.diystompboxes.com/smfforum/index.php?topic=76910.0