555 timer still ticking

[leeranya]

Hey everyone,
I tried using a 555 to flash a LED based on a potentiometer to change the flash interval time...
It worked perfectly for the LED, but for the sound signal it caused audible ticking to be heard whenever the LED is flashing.

I've tried to add a resistor and a 100uf cap to the 555 power source to try and regulate it, reading in the forum that it's due to the "crowbar" effect on the power source, but it didn't help. Then, someone told me to use a CMOS version of the 555 to stop the crowbarring effect from happening. So, I ordered a few LMC555CN and put them on instead, but there is still ticking on the sound signal, which is absolutely detached from the LED circuit - the crowbarring seems to radiate from the LED circuit.

What do I do?

[newfish]

Hi.

From memory, last 555-based project I made used a 7555 (low power variety).

Also had a 47uF cap from the Anode of the LED to ground, and a 100pF cap from the circuit's output to ground.

I'll check when I get home, as I have the diagram somewhere...

Think this is right...  "http://www.iansnape.co.uk/schematics/" - the 'Tremolo Schematic 121108.sch' file is the one.  You'll need the splendid 'DIY Layout Creator' to view though.

Hope this helps.

[earthtonesaudio]

What do I do?

For the best advice, show us your circuit (draw a schematic).

The best advice, if you can't quiet the noise, would be to move the noise as far from the audio as possible, but maybe that's not practical.

If the CMOS 555 is still ticking, it may point to the current through the LED causing the noise, rather than the current through the 555.  The same tricks apply toward filtering noise from a flashing LED.  First, use a high-efficiency LED so you can get the same brightness from less current.  Second, you could try the same type of RC filtering (but smaller values for C) going to the LED, but unfortunately that will affect the timing of the flash.

[frequencycentral]

"Your 555 Ticking? Try this..." http://www.super-freq.com/?p=113

[leeranya]

hey guys
thanks for all your help - though nothing seems to work.

the schematic I'm using is this one:

the audio signal is disconnected from the 555 circuit, though they share their ground. I also added a potentiometer in addition to the resistor from pin 7 to 6 to control time.

[leeranya]

ok guys, after one month - the solution is to put a capacitor on the anode of the led (output of the 555) to ground...

thanks newfish!

[soggybag]

try this:



The whole circuit doesn't concern you just the parts from pin 1 to ground. The 1n4001 and the 100uf cap.

[brett]

Hi
the 555 has "totem pole" output that throws spikes.
The CMOS 555 (TLC555) uses a different output setup.  Enough power to flash your LED, but won't throw much in the way of spikes.
To be sure, decouple the power with a 0.1uF cap (preferably monolythic ceramic). The CMOS 555 will slow down the turn-on time, and reduce the problems from capacitatively coupled and radiated spikes.  (If you must stick with a bipolar 555, use a *big* capacitor (>22uF ?) in parallel with the LED.
cheers

[big bustle]

i'm having the same problem. i haven't had a chance to try these ideas yet.

i'm using the ne555p and ne555n

are these the cmos version of the 555? i checked the datasheet and searched for the word cmos and nothing came up.

also, what is the different between 555n and 555p?

[big bustle]

ok guys, after one month - the solution is to put a capacitor on the anode of the led (output of the 555) to ground...

thanks newfish!

what value cap did you use?

[newfish]

I had a 10pF cap and 3K9 resistor in parallel before the anode of the LED.

3K9 was to limit the current (and not damage the LED), and the 10pF cured my 'ticking'.

[big bustle]

I had a 10pF cap and 3K9 resistor in parallel before the anode of the LED.

3K9 was to limit the current (and not damage the LED), and the 10pF cured my 'ticking'.

i'm running a led and a vactrol off of my 555. i have my led current limiting resistors running off of the led cathodes. also i don't have a 10pf cap. the smallest i have is is .01uf.

are you running your 555 in asynchronous mode?

is this how your circuit is wired?



on another note i tried the diode and 100uf cap idea and that didn't work

[big bustle]

Hi.

From memory, last 555-based project I made used a 7555 (low power variety).

Also had a 47uF cap from the Anode of the LED to ground, and a 100pF cap from the circuit's output to ground.

I'll check when I get home, as I have the diagram somewhere...

Think this is right...  "http://www.iansnape.co.uk/schematics/" - the 'Tremolo Schematic 121108.sch' file is the one.  You'll need the splendid 'DIY Layout Creator' to view though.

Hope this helps.

hey new fish. i tried opening that file with both versions of diy layout creator (found here: http://www.diy-fever.com/index.php?project=software)  and it wouldnt work. 

[newfish]

Frommemory, I wired mine more like....

Pin 3 from the 555 (7555 in my case - just a lower current version I think) goes to the R/C network described above (3K9 and 10pF) then to the Anode of the LED.

LED Cathode goes to ground as normal.

I'll see if I can re-post / re-send as PDF the schematic tonight or tomorrow if that would help.

[big bustle]

i little update

i tried 3 different chips:

ha1755
ts555cn
ne555p

i did the diode cap combo

my 555 ground does not share a ground with the audio

and i found that using a cap (tried 47uf, 22uf and 10uf) from the indicator led anode to ground worked best.

interesting notes: when the led was bypassed it was noisiest

all chips were equally noisy with the diode/cap combo and anode to ground method. however removing the diode/cap i found the bipolar ne555p was quieter than the cmos ts555cn.

i wonder why that is

i'm now thinking the noise is coming from the switch. the audio path runs thru as well as the power to the led. i wonder if i wired the switch to cut off the led ground would make a difference. i also wonder if the switches im using might just be noisy themselves

[brett]

Hi

the bipolar ne555p was quieter than the cmos ts555cn

This can happen if the switching speed is an ingredient of the noise.  The cmos device switches 10x faster than the BJT version.  The fast slew rate (dV/dt and dI/dt) generates more intense magnetic fields.  Any audio circuit with high input impedance can pick this up.  That's one reason why I'd never use one of those (mad) 1+ Mohm buffers.  Except for tuning in to AM radio  .
cheers 

[big bustle]

Hi

the bipolar ne555p was quieter than the cmos ts555cn

This can happen if the switching speed is an ingredient of the noise.

The cmos device switches 10x faster than the BJT version.

the cmos version was plugged into the same ic socket as the bipolar and operating at roughly the same speed. so wouldn't that make yr theory invalid?

The fast slew rate (dV/dt and dI/dt) generates more intense magnetic fields.  Any audio circuit with high input impedance can pick this up.  That's one reason why I'd never use one of those (mad) 1+ Mohm buffers.

you lost me there. mad 1m ohm buffers? i assume yr talking about high impedance buffers pickuping up sound. why is that?


[/quote]

[Naz Nomad]

hey new fish. i tried opening that file with both versions of diy layout creator and it wouldnt work. 

HERE if you still need it ...

[big bustle]

thanks!

hey new fish. i tried opening that file with both versions of diy layout creator and it wouldnt work. 

HERE if you still need it ...

[newfish]

Have you tried the '7555' low current timers?

Same pin-out as a '555', but I've found them to be quieter.

Shown here as 'ICM7555IPA'... 

http://www.rapidonline.com/Electronic-Components/Integrated-Circuits/Timers-Signal-Gens./555-Timer-ICs/67451

Very cheap too!