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

[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.

[HankMcSpank]

Ok, my first attempt. I'm a beginner, so I welcome any comments towards a more efficient way of doing what I've just done (see code below)

I'm using the Microchip low count board...which only has 4 LEDs - the code I've kludged together below works fine as I turn the potentiometer on the Low Pin Count Board.

I don't think doing 'log' will be so tough after all (on account, there'll only be six LEDs involved when this is on the guitar, just a matter of tweaking with those individual thresholds to get it looking 'right').

My next attempt will be to get a sample & hold vibe going down (which I'm thinking will just be some form of short 'pause' in each of those 'blocks' & some resistors/caps in series with the LEDs?)

Start:
ADCIN 2, DC_In ; Read the DC level IN
DC_In = DC_In /2 '256 is too much resolution...cut it down by 50%
IF DC_In < 10 THEN
low PortC.0 
low PortC.1 
low PortC.2 
Low PortC.3
endif
IF DC_In > 25 THEN
HIGH PortC.0 
low PortC.1 
low PortC.2 
Low PortC.3
endif
IF DC_In > 55 THEN 
High PortC.0 
High PortC.1 
low PortC.2 
Low PortC.3
endif
IF DC_In > 85 THEN
High PortC.0 
High PortC.1 
high PortC.2 
Low PortC.3
endif
IF DC_In > 110 THEN
High PortC.0 
High PortC.1 
high PortC.2 
HIGH PortC.3
ENDIF
GOTO START
end

[toneman]

Ok, my first attempt. I'm a beginner, so I welcome any comments towards a more efficient way of doing what I've just done (see code below)

I'm using the Microchip low count board...which only has 4 LEDs - the code

which board??? which PIC??
I'm assuming U R using PicBasicPro(?)

just a matter of tweaking with those individual thresholds to get it looking 'right').

yes, this applies to analog and/or digital.

My next attempt will be to get a sample & hold vibe going down (which I'm

S&H usually refers to a gated analog capacitor with a HiZ buffer.
In digital "terms", U are storing the value(s) in binary and "delaying" the output processing via conditions.
Since U are already processing the input voltage signal level(one) for the digital AGC,
U already have the info. Just output it to a bunch of LEDs.
The refresh rate needs to only be fast enough so that it looks good to the eyeballs.

Sounds like a very interesting project.
Have U visited the DIYStompbox forum?
There is a "digital" section.
afn
T

[HankMcSpank]

which board??? which PIC??
I'm assuming U R using PicBasicPro(?)

This board ( with a 16f690 which is part of the PICKit2 beginners setup)...

http://ww1.microchip.com/downloads/e...e%2051556a.pdf

S&H usually refers to a gated analog capacitor with a HiZ buffer.

I've read that more than once...no matter how many times I read it, it's still not sinking in (the gated capacitor bit!)

Sounds like a very interesting project.
Have U visited the DIYStompbox forum?
There is a "digital" section.

I haven't but I will.

Re that code I posted above, hmmm, well - after posting it up, I realised it's not what I want (damn it...wish they had a delete button!) - it's just a simple LED level representation of signal level. What I want (what I really, really want) is a sample /hold representation ...I've spent a frustrating couple of hours, trying to do this with the PIC...it ought to be a piece of wII, but I actually spontaneously combusted (freaked the wife out a bit I can tell you...only because it made a terribly mess on the sofa)...just got back from the burns unit - I'll have another go, but will keep a fire blanket handy.

re the project - yep, it is a good 'un....all the elements are coming together, this LED level indicator is just bells whistles - totally unnecessary, but much sought after nevertheless!