Use of 555 timer for pulse detection

Thread Starter

MrVeee

Joined Aug 30, 2022
2
Hi

I've not really done any electronics like this for over 30 years. I've just started getting back into it but need a bit of advice.

I have a electronic drum kick pad that produces a pulse output (from a piezoelectric transducer I think). I want to use that pulse to generate 'closed circuit' lasting about 250ms each time it is triggered. So for each time a pulse from the drum pad arrives the drum sound module effectively sees it as a switch closed for about 250ms. I suspect I can probably do this with a 555 timer using the trigger input. The pulse from the drum pad appears to range from 0.5v (hitting it lightly) up to about 2.5v.:
Soft hit:
SDS00005.png
Hard hit:
SDS00008.png


I'm less sure about the output? I don't need to provide a signal as such. Just close the circuit so maybe I just need to send the output to a transistor to switch it 'on'?

Can anyone comment? Do you think I'm on the right track?

Thanks
Mike
 

Ian0

Joined Aug 7, 2020
6,293
Something like this should work. The piezo needs a high impedance load, so I would suggest a MOSFET such as BS170 on 2N7000, but they might need too much voltage to operate.7AF27B87-CD5E-48B2-96C2-559476EF28FE.jpeg
 

dl324

Joined Mar 30, 2015
15,112
Welcome to AAC!
Can anyone comment? Do you think I'm on the right track?
You need to invert the signal. If the input signal duration can be longer than 250ms, you need to AC couple it to the trigger input on the timer. You need at least 0.7V to turn on an NPN transistor. If the signal is less than that, you'll need some amplification.

If the closed circuit you need is something that is being switched low side, you can use an NPN transistor on the output of the timer. If it's some other configuration, you might need to use a relay.

More information will yield better suggestions.
 

crutschow

Joined Mar 14, 2008
30,788
To control the trigger threshold to the desired level, you could use a comparator to trigger the 555 (Ltspice simulation below):
Pot U4 allows adjustment of the Ref trigger threshold (red trace).
For this circuit, the Vin trigger period must be longer than the one-shot time of 250ms.

1661963854140.png
 
Last edited:

Thread Starter

MrVeee

Joined Aug 30, 2022
2
Many thanks everyone. I will sift through these answers and have a play around in Ltspice which I discovered a couple of days a go (and looks really good). I will probably have more questions!
 

dl324

Joined Mar 30, 2015
15,112
play around in Ltspice which I discovered a couple of days a go (and looks really good)
My advice is to not get too dependent on a simulator before you understand the basics yourself. Using a simulator to simulate a 555 timer is akin to using a calculator to add a couple 3 digit numbers.
 

crutschow

Joined Mar 14, 2008
30,788
Using a simulator to simulate a 555 timer is akin to using a calculator to add a couple 3 digit numbers.
That's a rather poor analogy.
I appreciate your prejudice against simulators, but a 555's operation is significantly more complicated then adding two small numbers, and seeing its waveforms in a simulation can significantly help understanding its operation in mho.
So my contrary advice is, do the simulations.
 

ericgibbs

Joined Jan 29, 2010
16,370
hi,
This authority is a supporter of Simulations being an advantage in teaching electronics.

E
https://www.researchgate.net/public...ctronics_Using_Visualization_and_Manipulation

Software for simulation-based learning of electronics was implemented to help learners understand complex and abstract concepts through observing external representations and exploring concept models. The software comprises modules for visualization and simulative manipulation. Differences in learning performance of using the learning software either with or without the simulative manipulation module were investigated in 49 college sophomores. The learning performance was higher for learning software utilizing simulative manipulation and visualization yields than for that lacking simulative manipulation, which suggests that learning performance can be enhanced if visualized learning can appropriately integrate simulative manipulation activities. An analysis of the learning process revealed that the use of simulative manipulation activities to verify and clarify the existing knowledge is crucial to improving the learning performance. © International Forum of Educational Technology & Society (IFETS).
 

Ian0

Joined Aug 7, 2020
6,293
Simulation would be good if the input waveform were well known.
In this case, considering how cheap the components are, there is a good case for building it and trying it out.
 

crutschow

Joined Mar 14, 2008
30,788
In this case, considering how cheap the components are, there is a good case for building it and trying it out.
I have no quibble with that.
Simulation can help design and understand a circuit, but it must always be built to verify its operation.
 

ericgibbs

Joined Jan 29, 2010
16,370
Hi,
I would agree that hardware models should be built where possible, to finally prove the design after simulation checks of a design

Humans, in general, find that visual imagery, is a quicker way to assimilate new information.

E

Footnote:
How many times have we asked a TS to post a circuit diagram, in order to understand his text description of a technical problem.?
 
Last edited:

crutschow

Joined Mar 14, 2008
30,788
Another advantage of simulation is that you can readily look at the voltages at any node, or the currents in any component, or even the difference voltage or current between two points, while displaying them all simultaneously, which is not really possible with the real circuit.
 

k1ng 1337

Joined Sep 11, 2020
681
That's a rather poor analogy.
I appreciate your prejudice against simulators, but a 555's operation is significantly more complicated then adding two small numbers, and seeing its waveforms in a simulation can significantly help understanding its operation in mho.
So my contrary advice is, do the simulations.
I find spice simulations very helpful in bridging the gap between theory and practice. The models are based on the mathematical relationships that exist in the components. Having the capability to change every parameter of a circuit on what is essentially a scope with unlimited probes is an undervalued tool.

I also really like how you present simulations as answers to questions. You provide the proof in a way that can easily be reproduced and simulated.
 
Last edited:
Top