# Controlling ~120 individual LEDs via PC

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#### sporkmasta

##### New Member
Hi all,
I am trying to design an guitar that has a light up fretboard in order to learn songs/scales. To do this I need to control about 120 individual, single color LEDs, and I am having trouble finding a good method. I've been researching for a few days now, and can't find a board with that many I/O pins to control. Ideally it would be connected to my computer in order to control the LEDs so I can input songs.
-Sporkmasta

#### blueroomelectronics

##### Well-Known Member
You can buy such a thing. Much easier than building it, it'll contain a microcontroller.
Optek Fretlight USB/LED Guitar - TrustedReviews - TrustedReviews

#### sporkmasta

##### New Member

Yea I actually have seen that. The guitar is kind of expensive and I want the learning experience/frustration

#### blueroomelectronics

It's an advanced project on many levels. With some fancy PC software to control it you could try a handful of $$SPI MAXIM LED controllers ICs and an FT245R USB to Parallel IC. #### MikeMl ##### Well-Known Member Most Helpful Member Use a m x n row/column matrix with the Leds/resistors at the intersections. You will have to scan them fast enough to get above the eye's flicker fusion freq. It takes two output ports, one m wide, and the other n wide. Decode the m port register to 1 of 2^m rows. Switch a positive voltage to the active row. Use the n port to drive n transistors which switch columns to ground. While any row is active, those leds that should be on will be turned on if the corresponding bit in the n output port is set high. m x n >= 120 #### marcbarker ##### New Member You could probably use fibre optics passed through tiny holes through neck, terminating in a countersunk hole filled with glass clear epoxy, maybe you could remove the truss rod (!) and pass the fibres down the channel. If you have inverse-parallell connected LEDs and used 'tristate' as an output state, can be much less IOs (12?) Last edited: #### jbeng ##### Member blueroomelectronics said: ... a handful of$$ SPI MAXIM LED controllers ...
The Maxim MAX7219 will control up to 64 leds per chip and they're about \$10US each. Obviously, to control 120 leds, you'd need 2. You'll also need a micro to format the display data for them.

marcbarker said:
maybe you could remove the truss rod (!)
Probably not a good idea!

Jeff

#### blueroomelectronics

##### Well-Known Member
Since the design needs PC software I figured the OP could bit bash SPI out on the FT245R and avoid a microcontroller.

#### jbeng

##### Member
I agree, a micro would only be required if the o/p wanted it to be self-contained. If the design it involves a PC, he could certainly use it to format the data and omit the micro.

Jeff

#### sporkmasta

##### New Member
Thanks guys for the input. I ordered a few samples of the Maxim 7221's to control the LED matrices. But I am unsure of how to connect two together, and how to control them using an FT245R. Any suggestions for a newb?

#### jbeng

##### Member
I've not used the FT245R, but the data I've seen says that it's a USB-to-parallel converter, correct? I would probably try it something like this...

Data bit 0 from the FT245 connects to the data input on the first 7221.
Data bit 1 connects to the clock input on BOTH 7221's.
Data bit 2 connects to the -CS line on BOTH 7221's.
The data output of the first 7221 connects to the data input of the second 7221.

This "cascading" of chips is illustrated on page 13 of the MAX7219/7221 datasheet. If you don't have the datasheet yet, download it. You'll need it to be able to talk to the 7221's.

Jeff

#### blueroomelectronics

##### Well-Known Member
The FT245R is basically an 8 bit I/O port, handy for bit bashing SPI or I2C data.

Either way the Optek Fretlight guitar would be cheaper for a one off purchase vs buying / learning / building / programming a DIY version.

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