LM3915 for Arcade Punch Meter Machine

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midmadness

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Hi,

This is my first post in the forum, hoping someone could give me suggestions on our group project.

The project specifies that we use LM3915, not for its common use like VU meter, but for other creative purpose. And I was lucky enough to convince our professor on this "easier" project, compare to the other group.:grin:

We came upon with the idea of using the 10 output of this IC for displaying ten levels of the commonly known arcade punch machine, and we intend to use a vibration sensor or piezoelectric sensor to absorb the punch and convert it to signal and be fed on the LM3915. That's the rough idea of it but the details is still in the limbo.

Could someone give me an idea on how much power a punch can generate or the power of the max signal we need to divide for each of the ten level.

Any suggestion is greatly appreciated!:thumbsup:

P.S. I just remember we also got another project in another subject in which we need to make a toy car turn left or right, either is fine it just need to turn, after each clap. We already got the idea of clap switch and the use of a twin motor gearbox but we haven't got the solution as to what relay we need to use to make one motor stop while the other continuously run to make it turn. Please do name the relay that could make this possible. Thanks!
 

If you read the LM3915 's data sheet, you will find out what voltage each Pin needs for an output But if I can remember right it has a Pin for a V reference so you can adjust and scale the output you desire. Read the data sheet and you'll be fine.
 


Hi

You'll have to do some research and determine the max impact force of a punch to be measured, then use a suitable "force" sensor. The sensor generally outputs pounds per millivolt. A sample and hold stage would be needed to store the measured value for input to an LM3914 where it would be displayed. Generally speaking, and depending on the power supply, the LM3914 can read up to 10 VDC max input and, I believe, as little as 125mv per step without additional scaling circuitry.

eT
 

The LM3914 has a 30dB range with 10 x 3 dB steps .

You must decide if you want to measure velocity, energy level (v^2), acceleration or g level of impact or displacement then which is more entertaining. Then how to filter the signal to extract the essential bandwidth and reject the noise (matched filter concept)

Even a ceramic cap can act as a piezo device if calibrated.

A bi-directional clap latch motor driver can be done as I saw once in the early 80's when I took one toy apart from my kids out of curiosity with only 5 or 6 tiny transistors (I forget)

High gain (200) CE audio amp from spring loaded fake antenna with electret mic. ANalog FlipFlop transistor circuit, saturated enough to drive motor in bridge mode and sensitive enough to be driven by audio envelope of clap pulse with RC coupling. It would also change directions when it hit the wall from bang and pivot steering mechanically in reverse then straight forward.

9V battery included.
 

SunnySkyguy said:
The LM3914 has a 30dB range with 10 x 3 dB steps .
Click to expand...
No.
The LM3914 is linear with equal level between steps so the range is 10 times which is 20dB. The level of the second step is 2 times the level of the first step, the third step is 3 times ... the 10th step is 10 times the level of the first step so it does not measure power accurately.
The LM3915 is logarithmic with 3dB between steps and a range of 30dB. It is good for measuring power.
 
A force sensor, like an electronic weighing machine would be like you hitting a brick wall 'cos it won't move much. My feeling is to use a very strong spring to hold a bar magnet halfway inside a solenoid. This would give you an acceleration output, but the harder you hit it, the faster and more it would move so it seems to me that it could do. Also it would have some finite movement.
I think you have to have a think about the display. Rather then use a sample and hold, I would try to latch the flying dot output on SR bistables with a timer to rest it after some suitable period (timer driven by an opamp directly from the solenoid). Or you could not use a timer, so the RS bistable stays set with its LED on, until the punch ball starts to move again. So the LEDs would jump from level to level.
Frank
 
Woah, I'm really really liking this forum! Thanks for the initial suggestions, I'll talk it over with my groupmates and come up with a better combination of hardware that's locally available, whether its a force sensor or a strong spring. I'll post updates and ask more questions as we push through with the project.

Again, I appreciate it all.
 

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