Police Flasher Circuit in a fuzz...with a problem

[joby]

I like to inject a little humor into my pedals. This fuzz pedal has a "police" theme and I want the indicator LED to flash red and blue. So, I've successfully built the fuzz circuit and the police flasher circuit (a simple alternating 2 LED circuit using a 555 timer).

The problem is that I can hear an audible oscillation in the fuzz at the rate at which the LEDs are flashing.

I'm using stripboard layouts for this right now, so these are two separate boards. The 555 timer board is running from the 9v as if it was just the standard indicator LED wiring: 9v+-->resistor-->LED anode-->Ground. So it's: 9v+-->555 board(+)-->555 board(-)--->Ground. So it is drawing power at the flashing rate from which the main fuzz board is drawing power, and I don't want that to be audible.

Main point: Is there a way to isolate/buffer/regulate, in some way, the power for each circuit so as to get rid of this problem? This is kind of an obscure question; I know i didn't get super specific with the actual boards. Admittedly, I am a bit of a novice, but still experienced. Any help would be massively appreciated.

[thermionix]

Funny, I had considered doing the exact same thing on a Rat clone.  I got a blue powdercoated 125B from Small Bear, and I thought it looked like "police" blue when I saw it.  So I thought, how cool it would be to have flashing red and blue LEDs on there!  I almost started a thread here to ask how to do that, because I know nothing about timers.  Then I thought about noise, especially in a high-gain pedal, and said screw that.

I'm sure it can be done, the noise can be isolated or filtered out, but you'll have to wait for someone smarter than me to come along and offer advice.  I'll be watching the thread though.

[italianguy63]

I've had some trouble with using color-changing LEDs in the past... they add a "scratchy/warble" like sound...

I have had some luck filtering them out (but not always).

Here is something you may try:

Assuming you have 2 LEDs.

In each LED chain-- add a 2nd small value resistor in series with the voltage dropdown resistor.  A value of 390R to 680R would probably be good.

Now between the point of the two resistors attach the positive leg(s) of electrolytic capacitors.  I have good luck with 47uF.

Attach the negative leg(s) to ground.

You may play with the value of the caps to see if you get better results.

This should help assuming the noise is from the LEDs.  If the noise is from the 555-- more may be required.

I am sure others will chime in too

MC

[Plexi]

Which is the resistors value? Maybe ypu should use something bigger.
I had some similar problem that I've solved using small consuming led and 10k resistor.

[bluebunny]

Try decoupling the power supply to your LED flasher boards (with a smallish resistor).  And try using a CMOS version of the 555 and low-current LEDs (with big CLRs), which will draw far less current and wobble the power supply lines less.

[duck_arse]

first off, welcome to the forum.
second off, +1 wot blue said.
third off - first off, use a 7555, or similar cmos type. run the timer supply from right after the supply polarity diode [if fitted, if series fitted] with a nice big electro bypassing the supply, and then an R//C supply line filter for the audio section. keep the timer grounds and the led grounds as seperate from the rest of the circuit as you possibly can.

AND - this just in - make sure your input cap, if using an electro, is the right way around!

[diffeq]

If you'd want to go CMOS, using simple 4011 would be much cheaper:  https://www.eleccircuit.com/two-led-flasher-by-gate-of-ic-4011/

I was considering CMOS 555/556 for some synth project and was surprised by the price, to be honest.

[joby]

overall folks, thanks for the replies. i will attempt some of these tip. again, i admit, i am novice enough to the point which some of this seems too technical for me. bid me good luck on figuring this out. i think it is a cool touch to have a red blue flash on a police fuzz . really thank you folks.

[bluebunny]

i am novice enough to the point which some of this seems too technical for me.

To quote Paul (I think): no-one is born knowing this stuff.  Wise words indeed.  So we've all been there - by definition.  Ask questions if anything is "too technical".  Then someone will be along to give you a fishing rod. 

[PRR]

> a simple alternating 2 LED circuit using a 555 timer

Maybe simple to you, but I think the rest of us need a schematic of what you actually built.

[Fancy Lime]

To throw in another alternative: The "Modified EA Tremolo" over on Home-Wrecker uses a discrete LFO that I'm pretty sure can be made to power to alternating LED's. Never had noise problems with that one as opposed to 555-based LFO's. Or use two of those EA Trem circuits with slightly different rates for an even more realistic "blinking interference" effect. Using dual pots you could control one rate with the Fuzz setting and the other one with the Volume setting. Oooh, now I wanna try this...

Cheers,
Andy

[antonis]

To throw in another alternative: The "Modified EA Tremolo" over on Home-Wrecker uses a discrete LFO that I'm pretty sure can be made to power to alternating LED's. Never had noise problems with that one

Lucky guy...!!! 

[duck_arse]

re: the pso -- nvmd, I might think on it some more .....

[edit :] .... if you string a clr/led/led/clr between V+ and ground, and connect the led/led junction to the collector of the pso, you will get sine-ish alternate winking. use supebrite leds and 47k-ish resistors, no probs.

[anotherjim]

But... if you mount the police flasher on your boot, then as you look down & operate pedals, it'll be just like the Naked Gun intro sequence. And if you wear a body cam, the audience could see that too?
I may be overthinking this?

[Fancy Lime]

re: the pso -- nvmd, I might think on it some more .....

[edit :] .... if you string a clr/led/led/clr between V+ and ground, and connect the led/led junction to the collector of the pso, you will get sine-ish alternate winking. use supebrite leds and 47k-ish resistors, no probs.

Hi Stephen,
yes, that would probably be the best way of doing this. However, since the OP self-identified as a novice I'll take the liberty of amending some explanations of your abbreviations

PSO: Phase Shift Oscillator, describes how the oscillator works. This is the thing that is used as an LFO in the EA Tremolo. https://en.wikipedia.org/wiki/Phase-shift_oscillator

LFO: Low Frequency Oscillator, means it operates (well) below audio frequencies

CLR: Current Limiting Resistor, the resistor that needs to be in series with an LED (or other diode) to keep it from burning up from too much current. Typically 2-50kΩ, depending on supply voltage and LED specifications.

The EA Tremolo schematic:
http://www.home-wrecker.com/eatremolo.html

The PSO can be further simplified by taking out the middle of the three 1µF caps and the 15kΩ resistor. It then produces a triangle instead of a sine wave, which probably makes little difference for your purpose.

Cheers,
Andy

[EATyourGuitar]

you could also use a TL072 setup as a comparator then clock divide the audio by 512 using 4024. I buffer the output of the 4024 with another comparator so I can use a two terminal bicolor LED.

[duck_arse]

it seems I'm never far from a pso .....

I put this on the bb, it works a treat. none of the values are critical, lots of transistors will do the job, you can set faster or slower speed. use your favourite high gain BC series Q and whatever value caps you have [220nF to 1uF I'd suppose - unequal values will work, but not tested]. speed is about right to my eye, but you'll hate it, so adjust as you see fit.



transistors with lower hFE's will work, but will reduce the swing at the collector, and the leds won't flash on/off so much as wink. the larger the load across Q1 (LED2 & R6), the lesser the swing, so lay off the low value clr's.

one thing about the led brightness - current for LED1 flows through the transistor to ground, so that current/brightness is set by R5. current for LED2 flows thru R1 and R6 [and R5 and LED1], so you need to add the values of R1 and R6 if you want to match the brites of the leds. when the transistor turns on, brighting LED1, it is shunting LED2//R6, so it goes dim. this is why you want to use superbright leds and nice large value CLR's.

also, I think this thing will drive you crazy if you try and run the leds bright - it's only for a geegaw, not an indicator.

[frequencycentral]

555 will crowbar the power supply. Replace it with a 7555 and you *might* be golden.

[thermionix]

PSO: Phase Shift Oscillator, describes how the oscillator works. This is the thing that is used as an LFO in the EA Tremolo. https://en.wikipedia.org/wiki/Phase-shift_oscillator

Police Siren Oscillator.  Jeesh.

[PRR]

> whatever value caps ...- unequal values will work...

For simplicity we often use three SAME caps and resistors. (Except in the BJT form, one resistor goes C-B for bias, so must be ~~100X bigger to account for Miller).

There is an "improved" form where the three C-R legs are "stepped" up in impedance (smaller C, higher R) as you go along. This allows a hair less gain in the amplifier. BJTs commonly have so much gain this is not warranted.

If the three C-R products are not very similar, you need more gain.

For one-knob variation over about an octave, plagiarize the old Fender tube amp trems. In BJT the impedances should be much lower, so you will need bigger caps. Note that often the first cap is 2X the others, and is loaded with a 10X spread of resistor from some higher to much lower than the other two resistors. This seems to be a good balance of oscillation parameters.

> drive you crazy if you try and run the leds bright

If you did need BRIGHT (say for a police car), the requisite low values at R5 R6 would load-down the amplifier's R1, and it would stall-out. While we could build a stronger oscillator, perhaps the better path is to just add an opamp (unity gain non-inverting is simple) to buffer the LED currents from the oscillator.

A cathode-follower would not buffer both ways, both LEDs. A pair of BJT as complementary emitter follower would work, but is as many pins and pennies as an opamp. And naked BJTs can pass more current than the LEDs can stand (if you go too low on R5 R6). The usual opamps are good for 30mA which will not quickly kill most LEDs.

You know we used to do this with a hot wire and a bi-metal contact.