Activate transistor with piezo disc

[Drottson]

So I believe this schematic is more accurate to the physical setup.

 

[CDRIVE]

Hi Drottson and thanks for trying to correct your schematic but it still has multiple errors. I'm late getting out and on my bike, so discussion regarding the errors will have to wait, unless someone else chimes in.

The max output current of the TLC555 is quite a bit lower than the Bipolar version but I don't think it'll be an issue here. They can also be used with much higher pull-up resistors than the bipolar version. This is going to be beneficial because the Piezo output impedance is also high.

So while I'm out cycling see if you can spot all the errors in your schematic. So far you've been doing a stellar job of trying on your own, without expecting everything to be done for you. In my mind there's a lot of value in that!

Chris

 

[Drottson]

Trying to find more errors in the schematic but I really think this one is correct now. I do however have the same problem. The cap C6 does not load while the white noise is generated, or at least it doesn't discharge when the noise stops. So I get an abrupt ending to the signal instead of the nice fade I got before when the cap kept feeding the white noise circuit with power a short while after the switch was turned off. This hasn't worked since I switched to the piezo trigger instead, and I can't understand why. Any ideas?

Oh, and I've recently discovered another problem (that I kind of was aware of but didn't think would be evident so soon). When I use a 9V battery the circuit functions well with a fresh battery but quickly it starts malfunctioning (mainly by not generating the noise, just faint clicks). When I hook it up to my DC power supply and set it a bit above 9V it works well all the time. So basically, when a fresh battery drops just a couple of hundred mV the circuit doesn't work anymore. Any ideas on how to fix this? I would VERY much like to use this with a 9V battery when it's completed.

 

[duke37]

R2 could be placed in parallel with R1 to eliminate DC bias on the piezo. I doubt if it will make much difference.

A diode in the output of the 555 to charge C6 when it is positive and to allow C6 to drop gently when it is zero may give you the fade which you crave.

 

[Alec_t]

The cap C6 does not load while the white noise is generated, or at least it doesn't discharge when the noise stops.

C6 is charged/discharged by the 555, not controlled by the white noise.
A dying battery will not be able to power the LM386 amp properly.

 

[CDRIVE]

View attachment 22254[/QUOTE]
R2 should not be connected to the piezo as shown. It should be connected between V+ and the 555 Trigger Pin 2.

C6 isn't doing anything more than creating a current surge when the Output pin goes high and low. You need a resistor between the 555 output pin3 and the junction of C6 & R4 to create a time constant ramp, if that's what you want..

The 386 data sheet indicates a capacitor (where you have R6) when configured as an amplifier.

Chris

 

[Drottson]

R2 should not be connected to the piezo as shown. It should be connected between V+ and the 555 Trigger Pin 2.

C6 isn't doing anything more than creating a current surge when the Output pin goes high and low. You need a resistor between the 555 output pin3 and the junction of C6 & R4 to create a time constant ramp, if that's what you want..

The 386 data sheet indicates a capacitor (where you have R6) when configured as an amplifier.

Chris

1. Not sure I follow, isn't this setup the same as what you drew in this only with the coupling cap added?

2. I see now what you mean. The way this is setup the discharge goes back through the 555 and to ground but when there was just a switch there before and that switch was released the discharge had nowhere else to go but through the white noise circuit. But I don't really see why a resistor should be added, wouldn't the diode that duke37 suggested in that position be better? Or perhaps you have another reason for that resistor? Maybe they should both be added?

3. Yes, but then I saw some schematics that used a resistance instead and the way I understood it the polarized cap works in pretty much the same way by adding resistance when it's loaded, but I may have misunderstood this completely. As I said, I'm quite new to all of this, so please enlighten me

EDIT: I've read up more on this and I see now why it should be a cap of around 10 uF instead. I think i mixed it up with the possibility of adding a resistor in series with that cap to control the amount of gain between 20 (nothing between pins 1 and 8) to 200 (cap between them, overriding the inner resistor of the 555).

Thanx again for your input guys!

 

[CDRIVE]

1. Not sure I follow, isn't this setup the same as what you drew in this only with the coupling cap added?

Quote Chris:
I didn't draw that schematic. It was pulled off the net. That said, I do remember addressing the coupling cap.. Here https://www.electronicspoint.com/th...or-with-piezo-disc.275538/page-3#post-1664943 and Here https://www.electronicspoint.com/th...or-with-piezo-disc.275538/page-3#post-1664959

2. I see now what you mean. The way this is setup the discharge goes back through the 555 and to ground but when there was just a switch there before and that switch was released the discharge had nowhere else to go but through the white noise circuit. But I don't really see why a resistor should be added, wouldn't the diode that duke37 suggested in that position be better? Or perhaps you have another reason for that resistor? Maybe they should both be added?

Quote Chris:
I misunderstood what you wanted. It appears that you want fast C6 charge time and slow discharge time. In that case you should do as Duke suggested and use a diode. A diode will charge the cap rapidly but prevent discharge back into pin3 when the 555 switches low. This will leave only the Emitter - Base junction of Q1 as the only discharge path for C6.

Thanx again for your input guys!

Chris

 

[Drottson]

Here's the latest version of the circuit. Now everything works smoothly. I also added some other stuff as suggested by the datasheet for the LM386, like the Zobel network before the speaker and a cap between pin 7 and ground instead of leaving it unconnected, which should reduce unwanted noise.

However there is still that issue with the battery failing to power this after just a few minutes. Does anybody have any ideas on how to work around this? I know a lot of DIY music effects and guitar pedals use the LM386 with just a 9V battery (pretty much standard voltage source for guitar pedals, even professional ones) so I figure there must be some kind of way. Tried to look around on a lot of DIY guitar pedal sites that post schamatics but none seem to adress this problem. Suggestions?

 

[Alec_t]

Is your 9V battery a reputable brand and fresh?
If so, check the current draw of your circuit; it may be excessive.

 

[CDRIVE]

Hi Drottson, you did a good job correcting the schematic. You get 4 gold stars!

Regarding your battery drain: The 9V battery isn't known for being a powerhouse but as you say others have been using them successfully in this application. Do as Alec suggested and measure your current draw. You can also double check the polarity of all the polarized caps in your circuit and insure they're connected as shown in your latest schematic.

Good luck,
Chris

 

[Colin Mitchell]

The 1M is not needed the two diodes are doing nothing and the 10k is doing nothing and the 1k is doing nothing and the 220R and the 3k and the transistor. How much more do-nothing do you want???
It's a do-nothing circuit.

 

[CDRIVE]

The 1M is not needed the two diodes are doing nothing and the 10k is doing nothing and the 1k is doing nothing and the 220R and the 3k and the transistor. How much more do-nothing do you want???
It's a do-nothing circuit.

Colin, you say the damnedest things. These statements can only make sense if you're referring to one of his schematics posted much earlier in this thread.

If you're going to comment in a thread please try to (at least) stay current.

EDIT: You can also try to be helpful occasionally. I don't think it'll kill you!

Chris

 

[Drottson]

Is your 9V battery a reputable brand and fresh?
If so, check the current draw of your circuit; it may be excessive.

It's a GP Greencell Extra Heavy Duty and I've used several batteries in the process, all fresh from the package and they basically fail after like half an hour, tops. You say measure the current draw, but I've never done that for a circuit this big. Where exatly should I put my amp meter? Or is it OK to just put it in series right about anywhere in the circuit?

About the caps being the right way I'm actually thinkingof just ripping it all of from the breadboard (again) and re-building it totally according to my latest schematic to ensure everything is the same but I figured I might as well do some current measurements before I do that.

 

[CDRIVE]

Drottson, more DMM's are damaged by improper use of measuring current than any other function. It's for this reason that I deleted an entire instruction procedure that attempted to cover various DMM function & range switch positions as well as Jack inputs.

Take a good photo of your DMM and post it, or post a link to a sales description of it. This way the instructions given will exactly match your meter.

On the other hand, if you have a 1Ω resistor you can disconnect the lead going from your protoboard to Battery(+). Connect the resistor between Bat(+) and the wire you just disconnected. Now you can use your DMM in the much safer (Volts) mode and measure the voltage drop across the resistor. The voltage drop will directly correlate to Amps (I=E/R).

Chris

 

[Martaine2005]

Hey Chris, are you using the E=I*R? I think Sweden uses V.
I could be wrong though. The thread is quite a read.

Martin

 

[CDRIVE]

Yes Martin but that's only because it's the way I was taught. Admittedly, Vacuum Tubes were in vogue at the time. E = Electromotive Force. Though, I don't think I ever knew how "I" translated to ("A") current. When I'm bored I'll Google it.

Cheers,
Chris

 

[Martaine2005]

I just did exactly that...
Andre'-Marie Ampere'. In the French language 'intensite' or something similar is intensity.
Obvious really when you know..
It finally makes sense...

Martin

 

[CDRIVE]

That's funny because I too googled it as soon as i posted that but I didn't score like you did.

Good job!
Chris

 

[GPG]

However there is still that issue with the battery failing to power this after just a few minutes. Does anybody have any ideas on how to work around this?

The noise is generated by avalanche current through the reverse biased b-e junction. Do some selection of transistors, as this is variable, to find one that is well below 9v