Build from scratch question about schematics (and hello to you all)


#1

Hello all,

I’m a not a Zynthian owner. Not yet. New to this forum as a member. For the past weeks I have read several threads here. What a great project this is.

I found the Zyntian a while ago read quite some forum posts and now I’m ready to build a Zynthian. From scratch. I mean that I didn’t order the kit, because I’m forced to do it as cheap as possible. So no easy to use pcb as the kit offers, but regular prototype board. And a Pifi Dac+ instead of a HifiBerry (but I will create a Hifiberry account anyway, just to vote for Zynthian :smile: )

The wiki shows on the pcb’s with the rotary encoders there are also capacitors. But those are not on the schematics. At least I don’t see them. The rotary encoders connect directly to the GPIO and the MCP23008.
http://wiki.zynthian.org/index.php/Building_a_Zynthian_Box_using_an_official_Kit#Electric_Scheme

Which are the schematics I should use for my build? The schematics on the wiki don’t seem to be the same as used for the pcb’s in the kit. Or do I misunderstand?


#2

Just build it without capacitor filters, they’re not critical at all
(this is my last build: Success Cases :wink: )


#3

Not critical?
Why are they used in the kit?


#4

They are for debouncing, but can also be anoying (read: Switch connected to MCP23008 of Controller 2 powers off my Zynthian )
I Did not use them (and also build from scratch): Success Cases

Succes!
Cheers,
Kees


#5

These capacitors are not “critical” but “convenient”. They debounce the encoder/switch signal and avoid that software debouncing algorithm consumes “high priority” CPU cycles (ISR). I recommend to use some kind of hardware debouncing circuitry with the encoders and switches, but you can ignore my recommendation and your Zynthian probably will work without problems :wink:

Regards!


#6

Are schematics for a debouncing circuitry available? I can solder and sort of read schematics, but I can’t design them. Why are the schematics different from the PCB’s in the kit ?

How can I know how often the software debouncing algorithm is invoked? And how much CPU time is used by the algorithm?


#7

I built my zynthian ‘classic’ with the larger debounce capacitor swapped with one of the smaller values and occasionally when turning that encoder fast there is a little hanging, I’ve also built a zynthian with no capacitors or ( the HIFI berry Amp + for zynthian spotters…) and I’ve had no problems. Might be different in a high electrical noise environment or with longer wires… .


#8

Well, I almost never had to put hardware debounce on rotary encoders in my projects… just one time I needed a low pass filter (something like the second schematic on this page http://www.dream-dimensions.de/2015/10/using-rotary-encoders/ ) but just because the firmware reading the encoder was stupid enough to crash with signals too fast :frowning:

But YMMV, as usual :slight_smile:


#9

The debouncing circuit in the kit’s PCb consist of 3 capacitor from the 3 signal encoder pins to ground. For the switch pin 100nF and for the 2 encoder pins, 10nF. I will fix the wikiw schematics ASAP :wink:

Regards,


#10

2 Observations, regarding the All in One schematic:

The encoder pin assignments seem to have changed from earlier versions,

old SW: pin 4, all in one SW: pin 2
old A: pin 2, all in one A : pin 4

(had an initial setback mixing old & new docs. re-implementing the circuit in my own layout)

High level signal levels of the MCP23017 I/O Expander are 4.3V (VDD – 0.7 min) with a 5V supply shown in the schematic, the SDA, INTA, INTB outputs seems to exceed Pi safety limits some have published. Short term encoder testing seems OK running the chip at 3.3V.


#11

The pin numbering convention is reversed in the All-In-One schematic. It’s a convenience question, but not a “real” change :wink: This is addressed with the JST connectors, that enforce the right connection. Sorry for the confusion :blush:

Yes. I’ve thought about this before, but i preferred to maintain these voltage levels in the All-In-One circuit because it worked perfectly in the older 2in1 circuit (and certainly it works perfectly in the newer All-In-One). Anyway, if you can verify that it also works with the lower voltage levels, i will change it in future versions.

Regards,