Hi all, I am working on a project measuring (and later processing) the readings of piezo pressure sensors. To be more exact, only the peak readings. A sensor is hit, produces a series of waves and I want to record the peak of the first wave and ignore the rest. After many YT tutorials, here's what I came up with so far. Please note this is just a first try for 1 sensor: // these constants won't change: const int piezo1 = 34; // the piezo is connected to analog pin 34 const int threshold1 = 200; // threshold value to decide when the detected sound is loud enough to be a real hit const unsigned long debounceDelay1 = 30; // time elapesed after the last peak reading before reading this sensor again, to debounce // these variables will change: int sensorReading1 = 0; // variable to store the value read from the sensor pin int currentReading1 = 0; // variable to int peakReading1 = 0; // variable to store the peak reading to later convert to a MIDI note unsigned long currentTime1 = 0; // unsigned long peakTime1 = 0; void setup() { pinMode (piezo1, INPUT); Serial.begin(9600); // use the serial port } void loop() { sensorReading1 = analogRead(piezo1); // read the sensor and store it in the variable sensorReading1 if (sensorReading1 >= threshold1) // only act if sensorReading1 is above threshold1 value { currentTime1 = millis(); // set currentTime1 for the if comparisson to debounce if ((sensorReading1 > currentReading1) && (currentTime1 > (peakTime1 + debounceDelay1))) // if the sensor reading1 is greater than the threshold1, greater than the previous reading and debounce time has elapsed {sensorReading1 = currentReading1;} // replace currentReading1 with the new value, it's going up if ((sensorReading1 >= threshold1) && (sensorReading1 < (currentReading1 - 10))) // if the sensor reading1 is greater than the threshold1 and is going down (past the peak), {currentReading1 = peakReading1; // note the previous reading as the peakReading1, as the last currentReading was the first going down (so after the peak) peakTime1 = millis();} // mark when the peakReading1 took place Serial.println (peakReading1); } } Please let me know where and how I could optimise this. Oh, and if I missed that there is a standard Arduino function that already does this, please enlighten me. My limited vocabulary on the subject doesn't always help me to find the functions available. I will use an ESP32 devBoard to run this on, as it is fast and cheap. Cheers, Hugo

The hardware is sorted. The sensor is run through a some resistors and has a schottky diode over the port in case of an overvoltage. I know / guess you mean well, please stick to the subject / question at hand. Thanks, Hugo

[image] HugoW: The hardware is sorted. That is what you think, but I have used these sensors in many projects, and I have access to an oscilloscope and know how to use it. But If you don't want me to tell you what you need to do then I will not.

That makes the two of us, then, on the oscilloscope bit. Although in all honesty I don't own one, I use the one at my job. So far, I have set a little circuit which gives me the readings the ESP32 can handle, with real-world inputs. That is enough for me, now. No doubt there is room for improvement, there always is, but good enough is what I settle for now, and I now focus on the question I posed. If you cannot suppress the urge to demonstrate your knowlegde on the hardware, please feel free to do so. I am not to old to learn, yet. But maybe we could handle that in a different bespoke topic. Hugo

In the meantime I found a mistake in my first code, line 27, I wrote the currentReading1 = sensorReading1 the wrong way around. And, I asked ChatGT for an alternative to my code, this is what it came up with: // Constants const int piezo1 = 34; // Piezo is connected to analog pin 34 const int threshold1 = 200; // Minimum value to register as a hit const unsigned long debounceDelay1 = 30; // Delay after a hit to debounce // Variables int sensorReading1 = 0; // Current sensor reading int peakReading1 = 0; // Detected peak value unsigned long lastPeakTime1 = 0; // Time of last peak detection bool isDetectingPeak1 = false; // State flag for peak detection void setup() { pinMode(piezo1, INPUT); Serial.begin(9600); // Initialize serial communication } void loop() { sensorReading1 = analogRead(piezo1); // Read the sensor value unsigned long currentTime1 = millis(); // Current time in milliseconds if (sensorReading1 >= threshold1) { // If the sensor value exceeds the threshold if (!isDetectingPeak1) { isDetectingPeak1 = true; // Start detecting a peak peakReading1 = sensorReading1; // Initialize the peak } // Update the peak value if the reading is higher if (sensorReading1 > peakReading1) { peakReading1 = sensorReading1; } } else if (isDetectingPeak1) { // If we were detecting a peak but the value dropped below the threshold isDetectingPeak1 = false; // Stop detecting lastPeakTime1 = currentTime; // Record the time of the peak Serial.println(peakReading1); // Output the peak value peakReading1 = 0; // Reset the peak for the next hit } // Optional debounce: Ignore readings for a short time after detecting a peak if (currentTime - lastPeakTime1 < debounceDelay1) { return; // Skip further processing } } I'm not sure how that works, yet, I'm slowly working through it. Hugo

[image] HugoW: Please let me know where and how I could optimise this. Does the code work? Optimise in what way, speed, memory RAM?

[image] HugoW: Please let me know where and how I could optimise this. [image] HugoW: Serial.begin(9600); That might be a start. [image] HugoW: The hardware is sorted. The sensor is run through a some resistors and has a schottky diode over the port in case of an overvoltage. Could you share a schematic? [image] How to make a schematic you can post. Tutorials When you submit a question on the forum you will usually need to add a schematic (circuit diagram). The tutorial that follows will explain some ways to create a useful image; however lets start by explaining how to add the image to your post. Its easy. Having created the image all you need to do is : Save the image somewhere convenient - maybe your desktop Start your post, and place the cursor (insertion point) where you want the image to be shown; [upload image to forum] 3: click th… What happens after the first signal peak value is detected? Do you have a time out setting? (not for debouncing).

what you describe could be implemented using a state machine. Here is a small introduction to the topic: Yet another Finite State Machine introduction curious to know more about how this is wired up exactly [image] HugoW: The sensor is run through a some resistors and has a schottky diode over the port

[image] HugoW: The hardware is sorted. So you are sure that you don't miss the peak value between two ADC samples?

Hmmmm, it seems the wiring of the piezo is very special... on my test-setup: Ring of the sensor is connected to ground. Centre of sensor is connected to signal (pin 34) Parrallel to the sensor I have a potentiometer. On the specific sensor I test with (see here for more detail: [millenium mps-850 drum kit modification] ), that potentiometer is set to about 8k Ohm. This gives me readings up to 3700 / 3750 when I hit the drum hard. Hitting the drum softly gives a value of 250-ish. If I connect the rim sensor, I have to turn the pot down a bit more. Is more sensitive, obviously. Eventually this 250 - 3750 range will be translates to MIDI velocity 0 - 127 (probably not linear and maybe 5 - 120 or something like that, but those will be settings just like the others). Parrallel to it all I have two 3V Schottky diodes, one reversed (don't ask me number, I just bought a bunch a while ago to protect ESP32 inputs). 3V gives a reading of 3839 on the port. I have tried a set-up with the centre of the sensor hooked up to 3V3, the ring to the pin 34 and a potentiometer between pin and ground. Effect is about the same, I see no benefits in this set-up. There are no doubt better solutions. What I need is a repeatable signal within the measurable range. I have that. There is no need to improve on that. Actually, this is the job I earn a living with. I come up with solutions (in many fields) that are good enough to serve the purpose. If my customer asks for 97% accuracy, I fail at my job if the solution I present is 98% accurate. I will have wasted resources. So, this way of sensing gives me the input I need, repeatable and usable. Hence, I use it. Anyway, the code ChatGPT came up with seems to work. I don't fully comprehend it, yet, but it works. I will now extend it to multiple sensors, all with there own settings. I will look into J-M-L's suggestion and I am still open for suggestions to simplify the code. The more simple, the more quickly it is running on the ESP32. Next in the proces will be to have two signals and two output values, one from the drum head and one from the rim sensor. Whichever has the highest value will get to play the MIDI note. This because when I hit the head, the rim sensor is triggered a bit, too, and vice versa. At the moment, the rim sensor overpowers the head sensor 90% of the time when the pot settings are the same, but with the pot settings set correctly and the peak readings sorted, the choice is easy. Hugo

this should be at the start of the loop (just after setting currentTime1) to be effective [image] HugoW: // Optional debounce: Ignore readings for a short time after detecting a peak if (currentTime - lastPeakTime1 < debounceDelay1) { return; // Skip further processing }

Find peak value of piezo sensor hit, multiple sensors

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johnerrington December 28, 2024, 9:47am 8

That might be a start.

Could you share a schematic?

What happens after the first signal peak value is detected? Do you have a time out setting? (not for debouncing).

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Find peak value of piezo sensor hit, multiple sensors

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