Hi guys! (and gals, been a long time since I don't post anything)
My name is Carlos Best. I'm from Argentina.
Recently I bough an old POD 2.0 wich uses de old line 6 pedalboard system (Floorboard or FB4)
Wich I have in mind is trying to clone one of those pedalboards.
1st: Availability: It's a discontinued product
2nd: Price. My POD cost roughly 100uss. Don't want to spend more than 100uss in a pedalboard RESEARCH FIRST:
I have found a VERY useful article wich analyzes the floorboard circuit.http://www.harmonicappliances.com/floorboard/floorboard.html
(It's down so I'm gonna reproduce it below. Credits to the author)
Also found some things herehttp://www.diystompboxes.com/smfforum/index.php?topic=36555.0
The idea of the resistor ladder was from here:http://groups.google.com/group/rec.music.makers.builders/browse_thread/thread/a9e6b84d8d42bd07/028f3019a3f15901#028f3019a3f15901
The POD & Floor Board use standard "Category 5" network cables for connection. The connectors on these cables (and the receptacles in the POD and Floor Board) are known as RJ-45s. They're just like standard phone jacks, but with 8 pins.
The pin numbering I'll use for RJ-type jacks starts at 1 and goes from left to right looking into the receptacle (the female socket on the POD or Floor Board) with the locking tab slot on the bottom, like the diagram on the right. "Standard" or not, that's the numbering I'll be using here.
I'll be referring to the various signals from the POD's point of view. The switches and pedals are inputs, and the LEDs are an output.
The diagram on the right shows the connections at the RJ-45 receptacles in the POD and the Floor Board. The three inputs to the POD (the two pedals and the switches) are all analog, but the LED output is digital.
The two pedal inputs are implemented using LEDs and phototransistors, with a shaded plastic strip moving between them as you move the pedal. The output of each phototransistor drives a 2N4401 transistor, and the output of the 2N4401s is the input to the POD. When connected to an operating POD, I've measured voltage levels on the pedal inputs from 0.25V to 4.1V. On my unit the two pedals don't have exactly the same range (one only goes down to about 0.4V).
The POD has some very strange (to me, anyway) circuitry on its inputs that I assume are for protection of the POD, so I've also looked at the Floor Board independently. When it's connected to a 5V supply (no POD) with 10k pull-ups on the Wah and Volume lines, the voltage range is a little lower (0.2V to 3.7V).
The switches are implemented as a resistor ladder. Each switch taps the series of resistors at a different point, making a variable voltage divider. The resistances are arranged so that some combinations of multiple switches are also detectable (see below). The POD appears to have the equivalent of a 1k pull-up on the Switches line.
The LEDs are controlled by a series of digital pulses whose lengths determine the on/off outputs of four shift registers connected to the three 7-segment LEDs and the various single-purpose indicators.
Switch Input Details
As mentioned above, the switches are connected to some kind of resistor ladder. The table below gives both the input voltages measured at the POD and the resistances from the Switches pin to ground with the Floor Board disconnected from the POD.
LED Output Details
The LEDs line carries a series of pulses whose widths determines the states of the various LEDs in the Floor Board. The POD always sends 32 pulses per update, which refreshes all four of the shift registers that latch the states of all the LEDs. The pulses are routed through a 7414 inverter that uses the pulse width to generate the clock and data signals needed by the 74HC595 shift registers.
Long pulses (3µs high, 3µs low) turn LEDs off and short pulses (1µs high, 5µs low) turn LEDs on. The POD keeps the line low between transmissions. Generally, the POD only shifts out the LED pulses when there is a change in the LEDs, but if any of the LEDs is blinking they're updated every 120ms or so.
The four bytes of LED states are sent MSB (bit 7) first. I will call them D0, D1, D2 and D3, with D0 being the first byte sent. I'll use D0.n to indicate an individual bit in D0, where the value of n ranges from 0 (LSB) to 7 (MSB).
The picture to the right of the table shows which segments correspond to which bits.
The "pointer" LEDs are the ones off to the left of the Distortion and Bank Down labels that tell you whether you're the POD is using the Floor Board in Effect On/Off or Channel Select mode. The question marks about the Wah LED will be resolved the next time I can borrow a digital scope from work for a day or two – I forgot about the Wah LED when I first looked at it…
I don't really understand the circuitry just inside the POD. There are diodes that appear to be intended to protect the POD against voltage spikes, and there is a pull-up effect that seems to be equivalent to 10-15K on the pedals and 1k on the switches.
Unfortunately it doesn't have any schems.
So here's the complicated part. Reverse engineering from theory to circuits
Thats what I did by now:
With the resistances table in the article I made a resistor ladder and simulated it with Electronic WorkBench.
After I made sure that the resistances and the voltages where more or less the same than those in the table I bought the components and voila. Everything worked ok. I had used a pot for the last resistor. That value is very important for the thing to work ok.
The only problem I had is the odd values of resistors. In the schem is specified the values I had used in series to achieve certain values.