Using Shruthi control board but without LCD and user controls

I realized that using the software editor and firmware patches I’ve been working on I can now control all parameters by software, including things like midi channel, board selection, patch naming and storage.

I own more filter boards than I do control boards, and building one control board for each filter gets a bit expensive (stacking or swapping them isn’t always an option). In order to minimize the costs of the control board, I realized I could do without any of the user input or lcd feedback.

Would it be ok to simply leave out the switches, pots and lcd from the control board? And would leaving out the LCD have a significant impact on relative power usage (allowing more units to do power daisy chaining)?

You’d probably want to ground the pot wipers at the very least to avoid the potential illusion of a ghost operator. Switches should be okay just being left off I suppose. But you can be sure someone else will expand on this!

ETA: It just struck me that this is the response of a semi-n00b to a total n00b. Should have first thought: “Hey, that’s 0x80, he ain’t no n00b”. Oh well…

Why dont you grab a bunch of 4051s and build a filter switch?

I like programming the patches for the specific filter attached. The resonance setting changes dramatically in sound between boards. Setting it to 50 might start self-oscillation on one but not the other, and of course the sound character changes too. I prefer to program a sound and have the patch stick with the filter it was designed for. Also some boards have options that others don’t of course, so switching manually between the dual svf, polivoks and digital filter boards is not really practical I think.

BorbaTheGeek, you’re not a n00b, your reply is correct.

Don’t solder the UI parts, but connect the pots wiper pin to a fixed voltage from one of the adjacent pins, ground or +5V.

Perhaps it would be a good idea to do that with the MISO pin too if the shift register chips are left out? Otherwise it might pick up noise that will then be interpreted as pressed switches?

Thanks everyone. I guess I’ll build an extra 4 control boards on the cheap then. Could start a Shruthi orchestra soon =]

@larsen: Which of the shift registers could be left out? I think I’d prefer keeping the leds for firmware / sysex dump feedback.

What’s a MISO pin?

if you want to keep the leds you need to keep the 74hc595 and the 220r resistors
if you want to keep the buttons you need to keep the 74hc165 and the resistors array.

edit : I don’t know if the embedded pull-up resistors are activated on the shruthi standard firmware for the communication with the 165, but if not it takes probably just a very light firmware change to activate them, and not have any issue with floating pins because the 74hcxx pins would not have been mounted.

If you want to even omit the 74hc595, 74hc165 and resistor network (I thought that 0x80 wanted to omit only the expensive/harder to find parts), then larsen is right, you need to pull up pin 7 of the MCU, though a 100k resistor to make it easy to “override” by the ISP. If you pull it down instead, this will be equivalent to having all switches held low and the unit will always boot in firmware update mode. If you directly hook it up to GND or +5V, this will prevent the ISP programmer to operate and cause a short. So the only option is really to pull it up with a resistor.

If you do that, you can get away with the resistor network too!

IF you get rid of all that, would it be easier to just wire the Bits on a PerfBoard?

If you pull it down instead, this will be equivalent to having all switches held low and the unit will always boot in firmware update mode. If you directly hook it up to GND or +5V, this will prevent the ISP programmer to operate and cause a short. So the only option is really to pull it up with a resistor.
I’m sorry for the annoying question, but wouldn’t the internal pull-up resistor do the job just as well?

Yes, but then you have to change the code, and since you have to change the code, you might as well just disable the bit scanning the switches :smiley:

ah… this explains why i could not get the muboot working on my shruthipal…

@pichenettes > well, that makes sense…
But more generally, is there an advantage of not activating the pull-up resistor for this pin (and maybe some others) for the usual setup of the shruthi? power consumption?

There’s no reason - it’s just not necessary with the standard hardware in which the input pin is driven by the 165 output…

I’m working on simillar thing - triphonic SSM Shruthi with two additional cores running on small devboards.
There’s no success starting firmware without hardware UI (pichenettes, thanks for tip, I didn’t know about pulling pin 7 high to pass bootloader) so I had to rebuild firmware.
After that it runs on one board but won’t run on other two. This is what I’m stuck with at the moment, there’s something wrong with this boards.

I was originally only interested in keeping out the expensive and hard to find parts yes, but it’s good to know the other options. Having nothing mounted at the top would make it nice and compact!

I guess using a dev or perfboard board would be a sensible if you leave so much out, but I’m going with the standard pcb so I can expand it to a full version maybe later and easily stick it on the filter board.