Arduino FM synthesizer shield - Page 1
Forum section: electronics / general

author: grenert
author_rank: Frequent Contributor
timestamp: March 25, 2016, 10:40:44 pm
content: Kickstarter project for a very cool FM synthesizer shield for Arduino. They have some examples of using it to make custom musical instruments.https://www.kickstarter.com/projects/1304489933/opa-multitimbral-fm-synthesizer-shield-for-arduino/descriptionA couple more days in the fundraising campaign. Seems like a neat project! Get your DX7 on

author: TonyD
author_rank: Contributor
timestamp: March 26, 2016, 12:50:25 am
content: Looks cool.Is that a dsPIC they're using for the synth engine?

author: Someone
author_rank: Super Contributor
timestamp: March 26, 2016, 03:55:21 am
content: "interesting" routing on those boardsI thought the DX7 algorithms were quite low on resource requirements, and largely lookup tables. From the basic structure a 4 operator voice like those should be able to run directly on an atmel mega with plenty of RAM/ROM, 8 operator and 16 notes of polyphony would need around 200MIPS.

author: grenert
author_rank: Frequent Contributor
timestamp: March 26, 2016, 02:21:26 pm
content: Quote from: Someone on March 26, 2016, 03:55:21 amHa ha, I hadn't noticed that before!The guy seems to be more of a programmer than a hardware guy. At least it seems to work well in the demo videos.Quote from: TonyD on March 26, 2016, 12:50:25 amYep.

author: marzac
author_rank: Newbie
timestamp: March 26, 2016, 04:16:17 pm
content: Hi everyone.I am Fred (aka Marzac), the guy behind the project development.Thank you for opening a thread here as it can interest some people in this community.I would like to answer the questions you asked.Someone =>You are right, this software is based on simple maths using a lot of LUTs.However, an Atmel Mega is a 8bit 20 MIPS MCU ...To render the 10 voices, I only use 70 MIPS because:- It is highly optimized (arithmetically speaking)- It makes heavy use of the DSP extensions of the dsPic- Audio rendering is entirely programmed in assemblyFor 16 voices I would around 90 MIPS but a dsPic is 70 MIPS so this is it.grenert & Someone =>What do you find "interesting" about the routing?I mean I am not an expert but have I been routing roughly ten commercial products with DSPs and MCUs that have successfully passed EMC tests and even FCC. I would like your comment on that because I do not get it.By the way, there is only one day left so if you want to help:https://www.kickstarter.com/projects/1304489933/opa-multitimbral-fm-synthesizer-shield-for-arduino/

author: neslekkim
author_rank: Super Contributor
timestamp: March 26, 2016, 04:45:51 pm
content: Quote from: marzac on March 26, 2016, 04:16:17 pmI wouldn't know, but I guess lot of straight parallel lines on top, duck down an via, and lot of straight parallel lines on bottom, and no earth plane.I guess that would do something with parasitic capacitance and such?, but it seems to make awesome sound so... I'm on!, just hope you manage to get it funded.

author: marzac
author_rank: Newbie
timestamp: March 26, 2016, 05:04:47 pm
content: I wouldn't know, but I guess lot of straight parallel lines on top, duck down an via, and lot of straight parallel lines on bottom, and no earth plane.How does it matter?The design is made with a proper star-grounding scheme and the only fast signals path here are:- the traces between the DSP & DAC (less than 4mm long)- the traces between crystal & DSP (less than 3mm long)All the rest is DC or low frequencies. Traces are way too thick compared to current running.So I have not noticed a problem whatsoever.

author: grenert
author_rank: Frequent Contributor
timestamp: March 26, 2016, 08:33:19 pm
content: Practically speaking (how it sounds), it doesn't seem to matter for this design, but generally speaking, a lot of vias (and this board has a lot of vias) is considered bad PCB design practice. But that's more of an issue with high speed (RF) circuits and doesn't really matter here. Vias also create dead space on the board that is not supporting any components.But who cares, I agree it sounds great!

author: Someone
author_rank: Super Contributor
timestamp: March 27, 2016, 01:15:01 am
content: Quote from: marzac on March 26, 2016, 04:16:17 pmThank you for the actual numbers, they are close to my estimates and it looks like 4op with 4 voices could fit into an AVR mega.Quote from: marzac on March 26, 2016, 04:16:17 pmThe horizontal + vertical routing on opposite sides of the board are a common auotrouter pattern, other patterns can do better and a ground pour is usually "free" at the end anyway which is why it is unusual to see a board that does not have any ground pour. Routing to minimise loop area rarely comes up with such regular patterns and long parallel traces.