LED Bargraph chip (guitar LED bling-age) ..do with a PIC?

[HankMcSpank]

Just been looking at twinkler guitar (because deep rooted in every musician is LED bling just waiting to be mounted on his guitar)...

Originally discussed here...

http://projectguitar.ibforums.com/in...howtopic=41134

with a youtube video of the end end goal here...



Here's the chip they use....
http://www.national.com/ds/LM/LM3915.pdf

Now I'm fairly new to PICs, & even I reckon I could fairly quickly kludge some LEDs that light depending on the analogue input level, but I guess what separates my likely awful code from the likes of the h/w chip is the algorithm for fading the LEDs out smoothly (and the 3dB bit).

Has anyone done such a thing with LEDs? (not LCD bargraphs...nice bright, twinkly LEDS)...or would anyone have a good starting point ?

Ta,
Hank.

[toneman]

Hey Hank,
that's just a LED VU meter using a bargraph IC.
3915 is log while the 3914 is linear.
I'm using the 3914 with a PIC in a BatteryMonitorSystem(BMS) that I
am working on. For monitoring 18 batteries in real time.
U don't really need a PIC for this simple VU meter.
I've seen several "light shows" circuits using LEDs and bargraph ICs.
IIRC, Craig Anderton had a "blinky light machine" using bargraphs.
that's all I got for ya..... afn Tone

[HankMcSpank]

Hey Hank,
that's just a LED VU meter using a bargraph IC.
3915 is log while the 3914 is linear.
I'm using the 3914 with a PIC in a BatteryMonitorSystem(BMS) that I
am working on. For monitoring 18 batteries in real time.
U don't really need a PIC for this simple VU meter.
I've seen several "light shows" circuits using LEDs and bargraph ICs.
IIRC, Craig Anderton had a "blinky light machine" using bargraphs.
that's all I got for ya..... afn Tone

Thanks Tone,

I guess it's the log that would be most useful on a guitar. (the reason I want to use a PIC, is I'm putting on in my guitar anyway & it has lots of unused pins still! BLING!)

Just thinking here that to get the LEDs to fade rather than abrutly cut off, would problably need nothing more than a capacitor.

So...how on earth can log calculations on an analogue input be achieved on a PIC?

[Ioannis]

With a PIC it is a little difficult to do all the math and stil have time for the A/D and display.

Also for the Log function you might need floating point calculations (even slower...).

If 55-60db dynamics are enough for you with linear response then you have to:

1. amplify the signal to be in the range of 0-5 volt
2. use an absoluter value converter to feed the A/D of the PIC with just positive voltages
3. setup PIC to continusly read the analog value, make a small average and display it

If you insist on making it logarithmic then use an CA3089 or CA3189 chip and take advantage of the log amplifier that is used for the AGC and S-meter.

And if you want to do the math way, have a look at http://www.emesys.com/BS2math3.htm#Logtable

Ioannis

[toneman]

Hank and all,
I still think a PIC is overkill. Even if U have "extra pins" LOL!!
It's the software that will drive U insane!!! LOL!!!!!!!
The 3915 (and 3914) **are** A-2-D converters!
They are known as "flash converters" cause they just use a bunch of
comparators and convert the input V either to a bar or a dot...in a FLASH!
Really cool (and complex) would be to use a hexphonic guitar like a Roland-Ready Stratocaster and tap off the six preamps inside and split to six bargraphs!! IIRC, the bargraph IC just needs 2.5V for max level.
I'm using an expanded scale to measure a narrow voltage range for my BMS.
I also use a divide-by-2 attenuator to scale the approx 6V down.
For regular strat PUs, U should still use a singlesupply opamp as a preamp/buffer. I think either lin or log ICs would work fine.
The trick is to dial the gain of the preamp(direct from PUs), and dial in the bargraph to make a responsive looking display. Then, if U ran to 3 filters, low, mid, hi, U would have a triple LED bargraph lite show on your Axe!
But, where would U put all those LEDs?!?!?!?
LOL!!! <shakes his head> :-)

[HankMcSpank]

Hank and all,
I still think a PIC is overkill. Even if U have "extra pins" LOL!!
It's the software that will drive U insane!!! LOL!!!!!!!
The 3915 (and 3914) **are** A-2-D converters!
They are known as "flash converters" cause they just use a bunch of
comparators and convert the input V either to a bar or a dot...in a FLASH!
Really cool (and complex) would be to use a hexphonic guitar like a Roland-Ready Stratocaster and tap off the six preamps inside and split to six bargraphs!! IIRC, the bargraph IC just needs 2.5V for max level.
I'm using an expanded scale to measure a narrow voltage range for my BMS.
I also use a divide-by-2 attenuator to scale the approx 6V down.
For regular strat PUs, U should still use a singlesupply opamp as a preamp/buffer. I think either lin or log ICs would work fine.
The trick is to dial the gain of the preamp(direct from PUs), and dial in the bargraph to make a responsive looking display. Then, if U ran to 3 filters, low, mid, hi, U would have a triple LED bargraph lite show on your Axe!
But, where would U put all those LEDs?!?!?!?
LOL!!! <shakes his head> :-)

Funny you should mention Roland GK (as it goes I'm well into midi guitars - this is me )...becuase I'm presently designing a 6ch HEX sustainer driver to bo on my guitar (note: not a pickup.....the very opposite in fact), furthermore, I'm having to design my own bobbins in CAD, then cut them on a CNC machine I built (out of dot matrix printers!), so I can therefore cater for 6 LEDs to be mounted within the bobbin itself. (I already intend having an LED light under each string when it's plucked but figured an LED bargraph might be cool too!)

Re getting the guitar signal level up ....well my sustainer driver circuit alreeady does that. I simply want to go ther PIC route to save PCB real estate (there's not a lot of room in a guitar for big PCBs), & like I say, I'll already have a PIC on the PCB. I use the PIC for digital AGC for my sustainer (basically I AtoD the amplified incoming analogue signal then make some gain decision based on the corresponding DC level....with that in mind, I guess I'm 70% of the way there for LED bling already!

I think I'll give it a pop regardless...it ought to be fun....& like I say, you can never have enough LED bling!

Thanks for you comments.