The Lotus

[Peter Snowberg]

Hi all,

Some time ago I started playing with the Alesis-Semi SCR (Single Chip Reverb) and DSP1K, throwing several designs together under an umbrella design concept called "Soma". One of these designs I titled "Lotus" and as the months progressed the design ended up changing more than once. When I finally had something I was really happy with, a couple of technical problems got in the way of turning it into a finished design. EMI issues caused a completely intolerable level of noise to be present and the whole thing ended up in the scrap heap. There was just too much going on in too small a space. This was a little crushing.... not because of the amount of work that was thrown away in the end, but because I really wanted to bring an easy to program yet powerful and high quality DIY DSP effect to the light of day.

I guess I just needed to wait a little longer for the right parts to become available.

Spin Semiconductor has just released their first product which is a little DSP called the FV-1. This chip is closely related to the Alesis-Semi SCR in many ways, but it's a ground-up new design built around a whole bunch of lessons learned with earlier efforts.  As a result, we now have a DSP available for DIY reverb applications that gets beyond most of the previous barriers. THANK YOU KEITH BARR!

Welcome to the (next) Lotus.

[Peter Snowberg]

The Lotus:

The Lotus is a straight-forward DIY DSP reverb built around a single Spin Semiconductor FV-1. This design requires only four chips to build and there is no need to program a microcontroller which seemed to be a big barrier to many builders in previous designs.

Basic Lotus specs:
- One channel device with 24 bit Sigma-Delta A/D
- 1 second of delay memory
- 32.768KHz stock sample rate (48KHz also available by using a different crystal)
- Eight effects in a DIP-8 E2PROM (all changeable)
- Three effect parameter control knobs
- Mix control to vary the amount of DSP vs. dry signal
- Output level control
- Optional effect loop for inserting other (analog) processors.
- True bypass stompswitch (a 3PDT from Aron )
- On/Off and Clip LEDs
- Only 4 chips required(!)

OK, so who is interested?

[puretube]

 

[jmasciswannabe]

Ya, count me in! It will be my first attempt at dsp! Glad that something is coming out of the spin chip!

[bioroids]

I'm interested, I want to hear more. Are these chips difficult to get?

Miguel

[puretube]

http://www.diystompboxes.com/smfforum/index.php?topic=50833.0

[MetalGuy]

OK, so who is interested?

Are you kidding? Who is not interested?

[David]

I need a reverb.  The timing is utterly perfect!  Count me in!

[Peter Snowberg]

It really has surprised me how much the interest fades when people need to program a microcontroller to get something to work. I guess it only makes sense.

One of the really cool things about the Spin chip is that you no longer need to program anything to get a useful DSP effect working. 

While the Alesis-Semi SCR/Wavefront-Semi DRE chip does have algorithms built in, there is no ability to tweak them and who likes a flanger which is stuck on one speed or a delay which is hard-wired to one delay time? If it's not the right speed, the utility is limited. With the Spin FV-1, there are three analog inputs for control right on the DSP. This makes things much easier to deal with for most people and most importantly, there is no code to have to write for a host microcontroller. The earlier stuff I designed used a microcontroller to read the control pots, scale and bias the values, insert the resulting numbers into assembly language instructions, and then to finally "drip feed" the new control values into the DRE DSP where they got used. This was a very high overhead process, and now we don't need to deal with that any more. 

When this design process is complete, I hope to have something that is very similar in functionality to the Spin Eval board in that it will link directly with the Spin assembler. That will allow anybody to open a program, plug in a USB cable, and muck around with the DSP code to their heart's content. This will be an extention to the Lotus design that does this and it will include a couple more chips to make that capability available. The "basic" Lotus includes an 8 pin socket for an E²PROM which is where the effects are stored. Want different effects? Just plug in a new E²PROM.

Like previous designs, the effects built-into the DSP are not used in the Lotus, however, the code for the built-in effects is published on the Spin-Semi web site under an OPEN SOURCE license. Eventually, we'll have an Open Source DSP code repository here and you'll be able to customize your Lotus programs very easily. For those that just want to plug and play, it should be a really easy matter to get somebody to program an E²PROM for you.

[Peter Snowberg]

Here is a link to the Spin Semi downloads page. These effecs are published under an open source license.

http://www.spinsemi.com/downloads.php

I'm really loving the FV-1!!!

[Michael Allen]

so is there a project for this? sounds awesome

[Peter Snowberg]

It's on the way. I have the chips, but I'm between jobs at the moment and getting resettled.

[David]

Bump...   

Oh, Global Moderator the great and terrible, are you resettled yet?  Have you replanted your Lotus garden?