6 ms·

A vibrator helped me debug a motorcycle brake light system

128 points by mygnu 1y ago

latexr 1y ago
This is a blog post, so it should be a regular submission even if you’re the one you wrote it. https://news.ycombinator.com/showhn.html https://news.ycombinator.com/showhn.html > Show HN is for something you've made that other people can play with. HN users can try it out, give you feedback, and ask questions in the thread.
- mygnu 1y ago
  fair enough, thanks
- tomhow 1y ago
  We updated the title, thanks.
- deleted 1y ago
  [deleted]
theZilber 1y ago
Sheesh, talk about "taking a break"... I for sure approve this creative way to test things
doodlebugging 1y ago
I too have repurposed a similar machine to try to help me solve a nagging problem. One of my vehicles uses a hydraulic clutch. By design, air bubbles can be trapped in the master cylinder due to factory bends in the lines and the orientation of the master cylinder when it is properly installed. If this happens it will be impossible to shift the gears (manual transmission) until the air is bled from the lines. I tried multiple air burping procedures without success. Part of the procedure involves tapping on the hydraulic lines to help dislodge air bubbles so they can flow up and out of the lines into the fluid reservoir. The area is tight and in order to do this efficiently you must remove the master cylinder from the vehicle. I decided to avoid that removal step and employ a Sharper Image back massager as a tool to dislodge air bubbles with the system in place in the vehicle. Since that massager is huge it would not fit into tight places under the hood so I used a length of PVC pipe held tight to the lines to transfer the vibration to the lines. This allowed me to get large air bubbles out of the lines. In the end I was not able to remove enough air using this hack because an O-ring near the bottom of the system is missing or bad and that allows air to enter and flow up so i could vibrate that thing all day and never get anywhere. It was a shot in the dark anyway. If that O-ring were not missing or bad I know it would work.
- mh- 1y ago
  I'm given to understand there are multiple companies manufacturing those back massagers in different shapes and colors these days, if you need one that can reach into those tight places under the hood without relying on the PVC pipe to help it along.
  - doodlebugging 1y ago
    Sounds like a front massager. Different tools that certainly have their place, especially when there's no pipe handy.
    - goopypoop 1y ago
      yeah there's all sorts of useful shapes and convenient features, priced for every budget. Better in most ways! pipes just lead to trouble
      - doodlebugging 1y ago
        >pipes just lead to trouble I'm an old pipeliner. I can vouch for that.
      - MengerSponge 1y ago
        As I understand it you can even source them with specific bend and taper profiles, which lets you optimize for the geometry of the system you're trying to flush.
        dotancohen 1y ago
        I've seen one recently that seemed to be long and skinny enough where if OP could see the part, he could vibrate the part. I have no idea what part of the human anatomy such a device is necessary for. Maybe top-of-the-foot while standing?
        epcoa 1y ago
gpm 1y ago
Mildly related: "Evan and Katelyn" is the name of a youtube channel where (amongst other less mature things) they make a bunch of small things with concrete and epoxy, like a concrete keyboard. Both materials (especially concrete) need some assistance in flowing into small spaces and getting bubbles out. For the size of project they often work on... a personal vibrator seems to work damn well. Concrete keyboard video as an example: https://www.youtube.com/watch?v=HUSG5ohV0nY https://www.youtube.com/watch?v=HUSG5ohV0nY
- malfist 1y ago
  When I poured a pier for my telescope I did something similar with a sawzall
- Freak_NL 1y ago
  Similarly, I used a wired vibrator (more power) to get the bubbles out of body casting alginate. It makes sense. Specific professional tools to vibrate viscous fluids to get bubbles out of it exist (like those odd looking concrete vibrators), but for a small handheld vibrating tool there is already an enormous market of affordable tools which do just that.
- e40 1y ago
  Well, that was a deep rabbit hole.
  - DonHopkins 1y ago
    https://en.wikipedia.org/wiki/Rabbit_vibrator https://en.wikipedia.org/wiki/Rabbit_vibrator https://www.cosmopolitan.com/sex-love/advice/a4805/history-of-the-rabbit/ https://www.cosmopolitan.com/sex-love/advice/a4805/history-o...
- martin_a 1y ago
  Came here to comment that. I'm using a vibrator for exactly that purpose, too. Really helps with better surfaces on the parts I make for friends (and etsy).
landgenoot 1y ago
> Interestingly, adaptive brake light technology already exists in high-end vehicles. Isn't this mandatory in the EU? Edit. No. Only for passenger cars
mrheosuper 1y ago
> the sensor has its own built-in sample rate, 400 times per second. If I read it too quickly, I might just be grabbing the same number twice The author is configuring the sensor wrong i think. The usually way is you setup sampling rate of register, setup fifo inside register, wait for interrupt from sensor(through GPIO pin), then read from FIFO. Just blindly read data from sensor will get you in trouble, like reading duplicate value
- unwind 1y ago
  Not all microcontrollers[1]} have FIFOs for stuff like this, but perhaps you meant implementing it in software as a regular queue or something. Anyway, even easier since the OP seems to be dealing a lot with the time between samples, would be to just make sure that at least 2.5 ms have passed before reading the sensor again. Right? [1] Not sure if older blog posts detail the hardware, I do remember reading about this product on here before.
  - simgt 1y ago
    Their chip seems to be [0] an LIS3DH from ST, it has a fifo [1]. I actually haven't come across a modern IMU that doesn't have one. > would be to just make sure that at least 2.5 ms have passed before reading the sensor again You're resampling at the same rate by doing this, which won't be accurate due to very slight variations in timings. [0] https://cdn.shopify.com/s/files/1/0914/0181/4398/files/24-10-04_14-35-13_6253.jpg https://cdn.shopify.com/s/files/1/0914/0181/4398/files/24-10... [1] page 19, https://www.st.com/resource/en/datasheet/lis3dh.pdf https://www.st.com/resource/en/datasheet/lis3dh.pdf
  - mrheosuper 1y ago
    >Not all microcontrollers[1]} have FIFOs No, i mean the FIFO inside the sensor. The sensor will populate FIFO itself, and trigger interrupt to MCU when the FIFO is full(or half full, configurable)
lttlrck 1y ago
I used one to find the location of rattles in my car.
boltzmann-brain 1y ago
> It bumps up the debounce for next time ... > But when things are smooth for a while, the debounce comes back down it sounds like he's just incrementing a variable in the first case and using timers to decrement it in the second case. that's a bad implementation. the correct implementation here is an envelope follower, or maybe-perhaps a kalman filter. OP's implementation will exhibit motorboating: https://en.wikipedia.org/wiki/Motorboating_(electronics) https://en.wikipedia.org/wiki/Motorboating_(electronics)
giant_fern 1y ago
> Motorway is an hour out from where I live. Each tweak meant hopping on the bike and carving out hours to test. It's easier said than done, but you might want to approach this like a data science project. Record the data from your test runs, annotate the behaviour you want, and build up a dataset. You should be able to experiment with any number of tweaks (admittedly except for the data sampling itself) without having to get back on the bike.
- pavel_lishin 1y ago
  Yeah, I'm very surprised they didn't record the data from a single ride, with some sort of manual entry for "brakes should light up now", and then test at home.
speedbird 1y ago
Fun signal processing project and all the sampling problems sound typical. Unless this is just for your bike, given that some of the pokey fours run up to 15k rpm ~ 250Hz primary, I think it would be a lot easier to use a significantly higher sample rate and then treat in the digital domain. If you can recognise the engine speed and signal as a reliable pattern (use a digital PLL?) you might be able to subtract it and get more of the chassis signal left. As another poster pointed out, if you could do a motorway run with a high sample rate you have a good dataset to experiment with, including seeing how far you could downsample and still get appropriate sensitivity and selectivity.
lstodd 1y ago
On a bike you have the front brake lever at the throttle on the right hand. You always, always have to have at least two fingers on the brake lever and control the throttle with the thumb and palm. It is completely irresponsible to ride not doing that because sudden obstacle will not give you enough time to put them back on it. Then you lose 60-80% of braking power for a second or two. If you are doing it right then when you drop throttle you almost automatically slightly pull the brake lever. If the lever and brake light switch on it are adjusted properly like they should be, you have the brake lights on. Nice project, but..
- euroderf 1y ago
  On a motorcycle it is essential to have the mindset that they're out to kill you.
- maikhoepfel 1y ago
  I know a few bikers do something similar as you describe. I want to point out it is not generally accepted truth, e.g. the German ADAC explixitly teaches to keep fingers off the brake until needed. The idea being that if you're surprised by something, you're much more likely to slam the brake, introducing instability or locking up the front. You don't hover over the brake in a car either.
  - nickthegreek 1y ago
    The local state motorcycle training course will not allow you to cover the brake while learning. They consider it especially dangerous for new riders for the reason you stated.
    - lstodd 1y ago
      This looks counterproductive. I can get that when one first learns to ride and therefore has no idea of what to expect from the road and from the bike this sort of precaution might have some sense. For about first couple hundred of kilometers/miles. But no more than that. The whole point of learning to ride is to train yourself to always be prepared and situationally aware, to maintain total awareness of what you are doing, what is going on ahead and behind you, and keeping being able to correctly react as fast as possible whatever happens. Thus fingers on the brake. They are seriously out there to kill you. Be it distracted car drivers, sloppy road maintenance, stray dogs, bad weather, random idiots.. any of this will kill you if you relax. An occassional lowside or two in one's first two seasons most likely won't. Given even a mediocre protection set, one will get away with a bit of shock and maybe needing a new pair of pants. And a whole lot of training of the kind no school can give. Like when to pull the front brake and when to just open throttle and hope for the best. Besides there is a saying - if you do not crash once a season, you do not ride, period. Which is a grim reminder of that if one does not push oneself, one is losing skill. I ride for about 30 years already and this is true. Motorcycles are not safe and cannot be safe, safety isn't in the concept, and this is what we love about them.
gnfargbl 1y ago
From the original article, linked from this article: > Moreover, during intense braking scenarios, it flashes proportionately to the braking intensity. Is it just me who finds this behaviour to be a regression? If I see a brake light on a motorbike, I know that the bike is slowing, and I respond accordingly. An urgent flashing brake light doesn't make me react faster, but it does serve to confuse and distract my brain.
- RandomBacon 1y ago
  Flashing brake lights are super annoying. Flashing lights are attention-grabing and thus distracting when you are trying to observe the whole scene and not just fixate on the vehicle in front of you. Or if you are the type of driver that fixates on the vehicle in front of you, and a vehicle to the side has flashing brake lights, then it distracts you from the vehicle in front of you. They should be illegal, and they already probably are illegal - in my state, if the brake pedal is pushed, the brake light must be on, and if it is flashing, then it is alternating between on and OFF. (And a judge does not care if "technically it is 1% on and not completely off" - it looks off.) Next time you are in traffic, imagine if every vehicle in front of you had flashing lights.
bArray 1y ago
> So I needed a cheat code. Enter: a repurposed vibrator, No joke. I hooked it up to mimic the kind of high-frequency engine vibes you'd get ripping down a motorway. It wasn’t pretty, but it worked. I could test tweaks right from my test bench. Those massage guns could be quite useful too. When finding a problem in the field, replicating it on the lab bench is always ideal. > The current solution: The jitter helped, but it wasn’t bulletproof. Then I realized something deeper, the sensor has its own built-in sample rate, 400 times per second. If I read it too quickly, I might just be grabbing the same number twice. No new data. And if that repeat looks like a sustained deceleration, the light fires. It should be a de-bounce based on time, not based on an arbitrary sampling rate. So you are looking for an average value threshold over a sliding window based in time. Better yet: 1. On start-up it should be able to indicate an error via blink codes. You should for example be able to detect if an LED has burned out, there is moisture detected, that a brake signal was not detected over a X minute runtime, the temperature is outside safe limits, or the circuit draws current outside of the expected limits. 2. Use an IMU to detect de-acceleration events encase there is a break in the signal. It's obviously not ideal, but far better than nothing. Gravity is ~9.81m/s, and a braking force would be detected perpendicular to this. Again, you would use the error code on start-up to indicate that there is an issue. 3. Consider the use of an internal battery encase there is an issue with the supply voltage to the brake light. A bad power or ground could cause continuous resets, and failure to detect a signal.
throwaway894345 1y ago
This reminds me of a project I built in a class during my EE degree--I wanted a thing that would pick out the beat in a song and flash an LED accordingly. I thought it would be pretty easy to just look for spikes, but you can't have a constant threshold or else you will just run the LED for the entire duration of some high-energy portion of the song (or else you will hardly ever run it at all). It needed to be adaptive, but the adaptive threshold needed to be able to respond quickly to changes in the "average energy" of a song. It took quite a lot of calibrating to make it work properly, and I learned a lot in the process.

128 points by mygnu 1y ago

This is a blog post, so it should be a regular submission even if you’re the one you wrote it. https://news.ycombinator.com/showhn.html https://news.ycombinator.com/showhn.html > Show HN is for something you've made that other people can play with. HN users can try it out, give you feedback, and ask questions in the thread.

mygnu 1y ago
fair enough, thanks
tomhow 1y ago
We updated the title, thanks.
deleted 1y ago
[deleted]

theZilber 1y ago

Sheesh, talk about "taking a break"... I for sure approve this creative way to test things

doodlebugging 1y ago

I too have repurposed a similar machine to try to help me solve a nagging problem. One of my vehicles uses a hydraulic clutch. By design, air bubbles can be trapped in the master cylinder due to factory bends in the lines and the orientation of the master cylinder when it is properly installed. If this happens it will be impossible to shift the gears (manual transmission) until the air is bled from the lines. I tried multiple air burping procedures without success. Part of the procedure involves tapping on the hydraulic lines to help dislodge air bubbles so they can flow up and out of the lines into the fluid reservoir. The area is tight and in order to do this efficiently you must remove the master cylinder from the vehicle. I decided to avoid that removal step and employ a Sharper Image back massager as a tool to dislodge air bubbles with the system in place in the vehicle. Since that massager is huge it would not fit into tight places under the hood so I used a length of PVC pipe held tight to the lines to transfer the vibration to the lines. This allowed me to get large air bubbles out of the lines. In the end I was not able to remove enough air using this hack because an O-ring near the bottom of the system is missing or bad and that allows air to enter and flow up so i could vibrate that thing all day and never get anywhere. It was a shot in the dark anyway. If that O-ring were not missing or bad I know it would work.

mh- 1y ago
I'm given to understand there are multiple companies manufacturing those back massagers in different shapes and colors these days, if you need one that can reach into those tight places under the hood without relying on the PVC pipe to help it along.
- doodlebugging 1y ago
  Sounds like a front massager. Different tools that certainly have their place, especially when there's no pipe handy.
  - goopypoop 1y ago
    yeah there's all sorts of useful shapes and convenient features, priced for every budget. Better in most ways! pipes just lead to trouble
    - doodlebugging 1y ago
      >pipes just lead to trouble I'm an old pipeliner. I can vouch for that.
    - MengerSponge 1y ago
      As I understand it you can even source them with specific bend and taper profiles, which lets you optimize for the geometry of the system you're trying to flush.
      - dotancohen 1y ago
        I've seen one recently that seemed to be long and skinny enough where if OP could see the part, he could vibrate the part. I have no idea what part of the human anatomy such a device is necessary for. Maybe top-of-the-foot while standing?
        epcoa 1y ago

gpm 1y ago

Mildly related: "Evan and Katelyn" is the name of a youtube channel where (amongst other less mature things) they make a bunch of small things with concrete and epoxy, like a concrete keyboard. Both materials (especially concrete) need some assistance in flowing into small spaces and getting bubbles out. For the size of project they often work on... a personal vibrator seems to work damn well. Concrete keyboard video as an example: https://www.youtube.com/watch?v=HUSG5ohV0nY https://www.youtube.com/watch?v=HUSG5ohV0nY

malfist 1y ago
When I poured a pier for my telescope I did something similar with a sawzall
Freak_NL 1y ago
Similarly, I used a wired vibrator (more power) to get the bubbles out of body casting alginate. It makes sense. Specific professional tools to vibrate viscous fluids to get bubbles out of it exist (like those odd looking concrete vibrators), but for a small handheld vibrating tool there is already an enormous market of affordable tools which do just that.
e40 1y ago
Well, that was a deep rabbit hole.
- DonHopkins 1y ago
  https://en.wikipedia.org/wiki/Rabbit_vibrator https://en.wikipedia.org/wiki/Rabbit_vibrator https://www.cosmopolitan.com/sex-love/advice/a4805/history-of-the-rabbit/ https://www.cosmopolitan.com/sex-love/advice/a4805/history-o...
martin_a 1y ago
Came here to comment that. I'm using a vibrator for exactly that purpose, too. Really helps with better surfaces on the parts I make for friends (and etsy).

landgenoot 1y ago

> Interestingly, adaptive brake light technology already exists in high-end vehicles. Isn't this mandatory in the EU? Edit. No. Only for passenger cars

mrheosuper 1y ago

> the sensor has its own built-in sample rate, 400 times per second. If I read it too quickly, I might just be grabbing the same number twice The author is configuring the sensor wrong i think. The usually way is you setup sampling rate of register, setup fifo inside register, wait for interrupt from sensor(through GPIO pin), then read from FIFO. Just blindly read data from sensor will get you in trouble, like reading duplicate value

unwind 1y ago
Not all microcontrollers[1]} have FIFOs for stuff like this, but perhaps you meant implementing it in software as a regular queue or something. Anyway, even easier since the OP seems to be dealing a lot with the time between samples, would be to just make sure that at least 2.5 ms have passed before reading the sensor again. Right? [1] Not sure if older blog posts detail the hardware, I do remember reading about this product on here before.
- simgt 1y ago
  Their chip seems to be [0] an LIS3DH from ST, it has a fifo [1]. I actually haven't come across a modern IMU that doesn't have one. > would be to just make sure that at least 2.5 ms have passed before reading the sensor again You're resampling at the same rate by doing this, which won't be accurate due to very slight variations in timings. [0] https://cdn.shopify.com/s/files/1/0914/0181/4398/files/24-10-04_14-35-13_6253.jpg https://cdn.shopify.com/s/files/1/0914/0181/4398/files/24-10... [1] page 19, https://www.st.com/resource/en/datasheet/lis3dh.pdf https://www.st.com/resource/en/datasheet/lis3dh.pdf
- mrheosuper 1y ago
  >Not all microcontrollers[1]} have FIFOs No, i mean the FIFO inside the sensor. The sensor will populate FIFO itself, and trigger interrupt to MCU when the FIFO is full(or half full, configurable)

lttlrck 1y ago

I used one to find the location of rattles in my car.

boltzmann-brain 1y ago

> It bumps up the debounce for next time ... > But when things are smooth for a while, the debounce comes back down it sounds like he's just incrementing a variable in the first case and using timers to decrement it in the second case. that's a bad implementation. the correct implementation here is an envelope follower, or maybe-perhaps a kalman filter. OP's implementation will exhibit motorboating: https://en.wikipedia.org/wiki/Motorboating_(electronics) https://en.wikipedia.org/wiki/Motorboating_(electronics)

giant_fern 1y ago

> Motorway is an hour out from where I live. Each tweak meant hopping on the bike and carving out hours to test. It's easier said than done, but you might want to approach this like a data science project. Record the data from your test runs, annotate the behaviour you want, and build up a dataset. You should be able to experiment with any number of tweaks (admittedly except for the data sampling itself) without having to get back on the bike.

pavel_lishin 1y ago
Yeah, I'm very surprised they didn't record the data from a single ride, with some sort of manual entry for "brakes should light up now", and then test at home.

speedbird 1y ago

Fun signal processing project and all the sampling problems sound typical. Unless this is just for your bike, given that some of the pokey fours run up to 15k rpm ~ 250Hz primary, I think it would be a lot easier to use a significantly higher sample rate and then treat in the digital domain. If you can recognise the engine speed and signal as a reliable pattern (use a digital PLL?) you might be able to subtract it and get more of the chassis signal left. As another poster pointed out, if you could do a motorway run with a high sample rate you have a good dataset to experiment with, including seeing how far you could downsample and still get appropriate sensitivity and selectivity.

lstodd 1y ago

On a bike you have the front brake lever at the throttle on the right hand. You always, always have to have at least two fingers on the brake lever and control the throttle with the thumb and palm. It is completely irresponsible to ride not doing that because sudden obstacle will not give you enough time to put them back on it. Then you lose 60-80% of braking power for a second or two. If you are doing it right then when you drop throttle you almost automatically slightly pull the brake lever. If the lever and brake light switch on it are adjusted properly like they should be, you have the brake lights on. Nice project, but..

euroderf 1y ago
On a motorcycle it is essential to have the mindset that they're out to kill you.
maikhoepfel 1y ago
I know a few bikers do something similar as you describe. I want to point out it is not generally accepted truth, e.g. the German ADAC explixitly teaches to keep fingers off the brake until needed. The idea being that if you're surprised by something, you're much more likely to slam the brake, introducing instability or locking up the front. You don't hover over the brake in a car either.
- nickthegreek 1y ago
  The local state motorcycle training course will not allow you to cover the brake while learning. They consider it especially dangerous for new riders for the reason you stated.
  - lstodd 1y ago
    This looks counterproductive. I can get that when one first learns to ride and therefore has no idea of what to expect from the road and from the bike this sort of precaution might have some sense. For about first couple hundred of kilometers/miles. But no more than that. The whole point of learning to ride is to train yourself to always be prepared and situationally aware, to maintain total awareness of what you are doing, what is going on ahead and behind you, and keeping being able to correctly react as fast as possible whatever happens. Thus fingers on the brake. They are seriously out there to kill you. Be it distracted car drivers, sloppy road maintenance, stray dogs, bad weather, random idiots.. any of this will kill you if you relax. An occassional lowside or two in one's first two seasons most likely won't. Given even a mediocre protection set, one will get away with a bit of shock and maybe needing a new pair of pants. And a whole lot of training of the kind no school can give. Like when to pull the front brake and when to just open throttle and hope for the best. Besides there is a saying - if you do not crash once a season, you do not ride, period. Which is a grim reminder of that if one does not push oneself, one is losing skill. I ride for about 30 years already and this is true. Motorcycles are not safe and cannot be safe, safety isn't in the concept, and this is what we love about them.

gnfargbl 1y ago

From the original article, linked from this article: > Moreover, during intense braking scenarios, it flashes proportionately to the braking intensity. Is it just me who finds this behaviour to be a regression? If I see a brake light on a motorbike, I know that the bike is slowing, and I respond accordingly. An urgent flashing brake light doesn't make me react faster, but it does serve to confuse and distract my brain.

RandomBacon 1y ago
Flashing brake lights are super annoying. Flashing lights are attention-grabing and thus distracting when you are trying to observe the whole scene and not just fixate on the vehicle in front of you. Or if you are the type of driver that fixates on the vehicle in front of you, and a vehicle to the side has flashing brake lights, then it distracts you from the vehicle in front of you. They should be illegal, and they already probably are illegal - in my state, if the brake pedal is pushed, the brake light must be on, and if it is flashing, then it is alternating between on and OFF. (And a judge does not care if "technically it is 1% on and not completely off" - it looks off.) Next time you are in traffic, imagine if every vehicle in front of you had flashing lights.

bArray 1y ago

> So I needed a cheat code. Enter: a repurposed vibrator, No joke. I hooked it up to mimic the kind of high-frequency engine vibes you'd get ripping down a motorway. It wasn’t pretty, but it worked. I could test tweaks right from my test bench. Those massage guns could be quite useful too. When finding a problem in the field, replicating it on the lab bench is always ideal. > The current solution: The jitter helped, but it wasn’t bulletproof. Then I realized something deeper, the sensor has its own built-in sample rate, 400 times per second. If I read it too quickly, I might just be grabbing the same number twice. No new data. And if that repeat looks like a sustained deceleration, the light fires. It should be a de-bounce based on time, not based on an arbitrary sampling rate. So you are looking for an average value threshold over a sliding window based in time. Better yet: 1. On start-up it should be able to indicate an error via blink codes. You should for example be able to detect if an LED has burned out, there is moisture detected, that a brake signal was not detected over a X minute runtime, the temperature is outside safe limits, or the circuit draws current outside of the expected limits. 2. Use an IMU to detect de-acceleration events encase there is a break in the signal. It's obviously not ideal, but far better than nothing. Gravity is ~9.81m/s, and a braking force would be detected perpendicular to this. Again, you would use the error code on start-up to indicate that there is an issue. 3. Consider the use of an internal battery encase there is an issue with the supply voltage to the brake light. A bad power or ground could cause continuous resets, and failure to detect a signal.

throwaway894345 1y ago

This reminds me of a project I built in a class during my EE degree--I wanted a thing that would pick out the beat in a song and flash an LED accordingly. I thought it would be pretty easy to just look for spikes, but you can't have a constant threshold or else you will just run the LED for the entire duration of some high-energy portion of the song (or else you will hardly ever run it at all). It needed to be adaptive, but the adaptive threshold needed to be able to respond quickly to changes in the "average energy" of a song. It took quite a lot of calibrating to make it work properly, and I learned a lot in the process.