Sunday, September 6, 2009

potentially new Hollow Earth features..

I'm trying to squeeze the most out of this design. I've had a few feature requests and a lot of them were tap-tempo. Harmony-Central user crxsh had a good idea about making the soft-stomp, the one used for recording of shapes, multi-function. Specifically, being able to toggle it between record, tap-tempo and bank select.

I'm gonna see how feasable this is. It won't be ready for the next few batches as I still have PCBs to use up. Testing and optimizations also take time. But hopefully I'll get those to work. A three-way toggle switch could be placed on the side of the box next to the soft-stomp with a label describing the three states.

Another issue the Hollow Earth seems to have is that expression-out doesn't work with every pedal with expression-in, only some of them! I never intended it to be a main feature, just as a fun extra, but it seems more people want to use it than I had previously thought. I'll try and put some effort into increasing the compatibility of exp-out.

For the geeks, an expression pedal is basically a potentiometer. Potentiometers have three lugs, one for the minimum range, the max range, and the wiper. The way the Hollow Earth outputs expression control is by controlling an LED-LDR combo (an electrically-controlled pot), which due to its nature is the equivalent of an only 2-lug pot. While this works with many pedals with an expression-in jack, it doesn't work with those expecting 3-full lugs. So far, this includes the Eventide Timefactor and EHX HOG. I'll do my best to fix this in a later revision.


Julian said...

Hey man, this is Julian from haunting mids. I've been getting parts in for my tap tempo LFO/s+h/sequencer design, and I breadboarded the expression photocells in different configurations. I found that you need two photocells for it to work with the HOG. But to get the full range you need to have one LED be dark while the other LED is light. Which of course requires another output (you're using PWM to change the LED brightness right?)

Now I know you're using all your I/Os on the pedal, but I think I've come up with a work around for that. I think you can put all your switches on the same input, with the right resistor values and a GetRC statement and some math, the chip can figure out which ones are on and off, because each combination of on/off would yield a unique value if you do it right.

Anyways man, e-mail me. I've got some questions for you about Bascom.

cloudscapes said...

yeah, I kind of figured I'd need two photocells. I'll try and do that for the next batch of boards. I won't use an extra PWM output though. I'll just get the main one drive a transistor to invert the second LEDs brightness or something. this is gonan take some testing. I don't expect LED brightness to be linear.

that's a fantastic idea about getRC! I only tried it once and get pretty shitty results (integers between 0 and like 2 or 3 for the full 5v range). maybe I just wasn't implementing it properly. anyway, I gave it up too quickly. I'll do some tests tonight.

my regular pots could probably still use ADC for the precision, but for switches it's great! the resistance just needs to be in the general ballpark! thanks!

you really need a crystal oscillator for tap-tempo (which I don't use, lack of free pins). the internal oscillator fluctuates too much. if I free up some pins with getRC, I might be able to use a crystal afterall.

email me questions

cloudscapes said...

I might have to boost the chip to more than 8mhz too, with all the extra math

cloudscapes said...

getRC works but I can't use it. there's a delay when it gets a reading, seems like it can only do ten or so a second o nan 8mhz chip.

however, I will probably use this same idea but using the quicker ADCs