Problem with 555 ... #2

Thread Starter

Serik21

Joined Feb 23, 2018
62
Hello!
Mod:link to old Thread.E
https://forum.allaboutcircuits.com/...itivity-pot-in-my-circuit.145906/post-1259314

I know this is an ancient post but wonder if you are up for helping me one more time! Thanks to all the guidance i got on this post I have become much more adept at circuit building and circuitry in general. In fact my initial request seems so silly now.

I've been building the original circuits again ( the one-shot circuit ) and have come across an issue. One that i have built is sending a constant signal to the output and the 555 timer gets SUPER hot very quick. I've checked resistor values and pot functionality. Traced the circuit multiple times to ensure its correct, replaced both the 555 and 386 and verified voltage ( 4.9V ) . I dont think i can test the caps with my mutlimeter but am starting to think its a bad cap. Where should i start?

Also, if anyone is so inclined, could they explain exactly how the circuit works? I understand the voltage that comes from the piezo from my kick tower inputs in the the 386 audio amp, and it somehow takes that voltage and sends a signal to the 555 timer, which in turn triggers the transistor which in turn closes the ground loop on my output jack.

What's happening between the ICs? I assume the voltage that comes from the piezo is amplified through the 386 and then sent to the 555? And the 555 takes the signal and outputs it to the transistor for a variable amount of time? Why does the voltage cut in half on the IC?

I know im asking a lot, but any help is greatly appreciated!!

Thanks!

EEE drum head one shot.png
 
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sghioto

Joined Dec 31, 2017
2,094
Also, if anyone is so inclined, could they explain exactly how the circuit works?
Hello,
First off I don't see any reason for the 555 to get hot if the circuit is constructed exactly as the schematic unless the 555 is installed backwards, defective or not a true 555 chip as we have discussed before.
I don't have time right now to explain the operation but will later today.
Did you ever get a scope?
 

sghioto

Joined Dec 31, 2017
2,094
Also, if anyone is so inclined, could they explain exactly how the circuit works?
Detailed explanation of circuit operation.
The 555 in this circuit is configured for monostable operation, meaning when triggered it will send out a positive pulse for a duration that is determined mainly by the Pulse Width pot and the 10uf cap.
Pin2 of the 555 is the trigger pin. As long as the voltage on pin2 is above 1.7volts ( with a 5 volt supply) the output voltage on pin3 is low.

The LM386 audio chip is used as the trigger for the 555. The following pin #s refer to the LM386 only.
This works because the nominal voltage on the pin5 is 1/2 the supply or 2.5 volts. This is higher then 1.7 volts so the 555 output remains low.
The output from the KP-65 connects through the 100K pot to pin2 the negative input. A signal from the KP-65 is amplified and reduces the voltage on the output pin5. When this voltage is below 1.7 volts the 555 is triggered.

The 2N3904 transistor inverts the output from the 555 to a negative pulse which is required going to the "brain".

This is the basic operation without getting more technical. Hope this will help.
SG
 
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Thread Starter

Serik21

Joined Feb 23, 2018
62
Hello,
First off I don't see any reason for the 555 to get hot if the circuit is constructed exactly as the schematic unless the 555 is installed backwards, defective or not a true 555 chip as we have discussed before.
I don't have time right now to explain the operation but will later today.
Did you ever get a scope?
I didn't get a scope but may need to invest. The 555 and 386 come from digikey like you suggested. The rest of the components were amazon specials though, so maybe that's my issue.
 

Thread Starter

Serik21

Joined Feb 23, 2018
62
Detailed explanation of circuit operation.
The 555 in this circuit is configured for monostable operation, meaning when triggered it will send out a positive pulse for a duration that is determined mainly by the Pulse Width pot and the 10uf cap.
Pin2 of the 555 is the trigger pin. As long as the voltage on pin2 is above 1.7volts ( with a 5 volt supply) the output voltage on pin3 is low.

The LM386 audio chip is used as the trigger for the 555. The following pin #s refer to the LM386 only.
This works because the nominal voltage on the pin5 is 1/2 the supply or 2.5 volts. This is higher then 1.7 volts so the 555 output remains low.
The output from the KP-65 connects through the 100K pot to pin2 the negative input. A signal from the KP-65 is amplified and reduces the voltage on the output pin5. When this voltage is below 1.7 volts the 555 is triggered.

The 2N3904 transistor inverts the output from the 555 to a negative pulse which is required going to the "brain".

This is the basic operation without getting more technical. Hope this will help.
SG
Thanks a ton for this. It helps a lot.
 

sghioto

Joined Dec 31, 2017
2,094
The only thing I see that's different from the schematic are the 1uf caps on pin5 of the LM386 and pin5 of the 555.
They should be .1uf
What are the voltage measurements on both chips?
 
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