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

**URL:** <https://discourse.zynthian.org/t/build-from-scratch-question-about-schematics-and-hello-to-you-all/1006>\
**Category:** Building Zynthian\
**Created:** [August 21, 2017, 6:29pm UTC](https://discourse.zynthian.org/t/build-from-scratch-question-about-schematics-and-hello-to-you-all/1006 "2017-08-21T18:29:57Z")\
**Posts on this page:** 11\
**Page:** 1

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**Author:** ![Marcel](https://discourse.zynthian.org/letter_avatar_proxy/v4/letter/m/71e660/32.png) [@Marcel](https://discourse.zynthian.org/u/Marcel)\
**Post date:** [August 21, 2017, 6:29pm UTC](https://discourse.zynthian.org/t/build-from-scratch-question-about-schematics-and-hello-to-you-all/1006/1 "2017-08-21T18:29:57Z")

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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 😄 )

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](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?

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**Author:** ![Axeman](https://discourse.zynthian.org/user_avatar/discourse.zynthian.org/axeman/32/278_2.png) [@Axeman](https://discourse.zynthian.org/u/Axeman)\
**Post date:** [August 22, 2017, 7:53am UTC](https://discourse.zynthian.org/t/build-from-scratch-question-about-schematics-and-hello-to-you-all/1006/2 "2017-08-22T07:53:57Z")

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Just build it without capacitor filters, they’re not critical at all  
(this is my last build: [Success Cases](https://discourse.zynthian.org/t/success-cases/41/42?u=axeman) 😉 )

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**Author:** ![Marcel](https://discourse.zynthian.org/letter_avatar_proxy/v4/letter/m/71e660/32.png) [@Marcel](https://discourse.zynthian.org/u/Marcel)\
**Post date:** [August 22, 2017, 10:04am UTC](https://discourse.zynthian.org/t/build-from-scratch-question-about-schematics-and-hello-to-you-all/1006/3 "2017-08-22T10:04:24Z")

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Not critical?  
Why are they used in the kit?

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**Author:** ![Keeze101](https://discourse.zynthian.org/user_avatar/discourse.zynthian.org/keeze101/32/21_2.png) [@Keeze101](https://discourse.zynthian.org/u/Keeze101)\
**Post date:** [August 22, 2017, 7:25pm UTC](https://discourse.zynthian.org/t/build-from-scratch-question-about-schematics-and-hello-to-you-all/1006/4 "2017-08-22T19:25:36Z")

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They are for debouncing, but can also be anoying (read: [Switch connected to MCP23008 of Controller 2 powers off my Zynthian](https://discourse.zynthian.org/t/switch-connected-to-mcp23008-of-controller-2-powers-off-my-zynthian/24/10?u=keeze101) )  
I Did not use them (and also build from scratch): [Success Cases](https://discourse.zynthian.org/t/success-cases/41/12)

Succes!  
Cheers,  
Kees

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**Author:** ![jofemodo](https://discourse.zynthian.org/user_avatar/discourse.zynthian.org/jofemodo/32/2_2.png) [@jofemodo](https://discourse.zynthian.org/u/jofemodo)\
**Post date:** [August 22, 2017, 8:59pm UTC](https://discourse.zynthian.org/t/build-from-scratch-question-about-schematics-and-hello-to-you-all/1006/5 "2017-08-22T20:59:32Z")

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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 😉

Regards!

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**Author:** ![Marcel](https://discourse.zynthian.org/letter_avatar_proxy/v4/letter/m/71e660/32.png) [@Marcel](https://discourse.zynthian.org/u/Marcel)\
**Post date:** [August 22, 2017, 10:21pm UTC](https://discourse.zynthian.org/t/build-from-scratch-question-about-schematics-and-hello-to-you-all/1006/6 "2017-08-22T22:21:17Z")

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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?

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**Author:** ![wyleu](https://discourse.zynthian.org/user_avatar/discourse.zynthian.org/wyleu/32/514_2.png) [@wyleu](https://discourse.zynthian.org/u/wyleu)\
**Post date:** [August 23, 2017, 7:46am UTC](https://discourse.zynthian.org/t/build-from-scratch-question-about-schematics-and-hello-to-you-all/1006/7 "2017-08-23T07:46:38Z")

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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… .

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**Author:** ![Axeman](https://discourse.zynthian.org/user_avatar/discourse.zynthian.org/axeman/32/278_2.png) [@Axeman](https://discourse.zynthian.org/u/Axeman)\
**Post date:** [August 23, 2017, 8:03am UTC](https://discourse.zynthian.org/t/build-from-scratch-question-about-schematics-and-hello-to-you-all/1006/8 "2017-08-23T08:03:32Z")

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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/](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 ☹

But YMMV, as usual 🙂

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**Author:** ![jofemodo](https://discourse.zynthian.org/user_avatar/discourse.zynthian.org/jofemodo/32/2_2.png) [@jofemodo](https://discourse.zynthian.org/u/jofemodo)\
**Post date:** [August 23, 2017, 8:18am UTC](https://discourse.zynthian.org/t/build-from-scratch-question-about-schematics-and-hello-to-you-all/1006/9 "2017-08-23T08:18:15Z")

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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 😉

Regards,

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**Author:** ![MaxMaxis](https://discourse.zynthian.org/letter_avatar_proxy/v4/letter/m/90db22/32.png) [@MaxMaxis](https://discourse.zynthian.org/u/MaxMaxis)\
**Post date:** [December 31, 2017, 6:47pm UTC](https://discourse.zynthian.org/t/build-from-scratch-question-about-schematics-and-hello-to-you-all/1006/10 "2017-12-31T18:47:21Z")

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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.

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**Author:** ![jofemodo](https://discourse.zynthian.org/user_avatar/discourse.zynthian.org/jofemodo/32/2_2.png) [@jofemodo](https://discourse.zynthian.org/u/jofemodo)\
**Post date:** [January 3, 2018, 4:22pm UTC](https://discourse.zynthian.org/t/build-from-scratch-question-about-schematics-and-hello-to-you-all/1006/11 "2018-01-03T16:22:51Z")

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> [@MaxMaxis](#):
>
> The encoder pin assignments seem to have changed from earlier versions,

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

> [@MaxMaxis](#):
>
> 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.

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,