Input/ Output Stages

9 years 3 months ago #272 by chrisjohnhilton
Hey!
Pretty new to electronics in general, but I'm just wondering if someone could go threw the design of the input/output stages in abit more detail? As in, why certain things are there? What does the tp1/tp2/tp3 point mean? Would just like to learn more about it and have a greater understanding, than just build it and be done... if that makes sense?

Thanks,
Chris

Please Log in to join the conversation.

9 years 3 months ago #273 by Ray
Replied by Ray on topic Input/ Output Stages
Hi,

When we first wrote the article about pedalSHIELD we did not go very technical to keep it simple and not to scare the people with formulas, filters and gain calculations

But I see that learning how the circuit really works and gaining information to create your own designs is very interesting, so I will get some time to write something more technical and complete about the pedal hardware and why the things where designed like that.

In the meantime I can give you some directions:
1- The first op-amp of the input stage is basically an MXR Micro Amp, you can have a look to the analysis.
2- The second op-amp of the input stage is an inverting buffer with some caps (C5 and C4) to remove highs and lows.
3- Then we have two clamping diodes to protect the arduino DUE board from voltage peaks.
4- The 3rd and 4th op-amps are a differential and a summing amplifier respectively, t here is a GREAT book by Mancini explaining this topologies among others.
5- Then we have some bits and bolts, like a ±5 power supply with a TC1044 and some pots switches and leds connected to Arduino.

I hope this keeps you busy!!! :evil: :guitarsg: :ampvox:

Please Log in to join the conversation.

9 years 2 months ago #282 by chrisjohnhilton
Thanks for your reply!
The info on the MXR Booster being used as influence has helped in my understanding massively!
Looking at other projects getting guitar signal into an arduino, the signal in amplified, then a DC offset is required to move the centre voltage to 2.5V, allowing the Arduino to read the whole of the signal, right? Do the pedalShield not do this? Or am i just not clever enough to spot where it's happening on the schematic... haha Or 2nd opamp achieving this?

Chris

Please Log in to join the conversation.

9 years 2 months ago #285 by Ray
Replied by Ray on topic Input/ Output Stages

Looking at other projects getting guitar signal into an arduino, the signal in amplified, then a DC offset is required to move the centre voltage to 2.5V, allowing the Arduino to read the whole of the signal, right? Do the pedalShield not do this?


Yes, the input stage amplifies the guitar signal, gives some high/low pass filtering to remove unwanted frequencies and add an offset voltage.
The DC offset is needed, in the Arduino DUE the DACs work from 0 to 3V3, so the offset voltage is 1.65V(3V3/2).
This offset is created in the input stage by the voltage divider created by R19 and R20 and applied trough the biasing resistor R2.

I hope it makes all a bit more clear, some other boards (like Arduino UNO) use another biasing, to 2.5V because its ADCs work from 0 to 5V.
The following user(s) said Thank You: firecoke

Please Log in to join the conversation.

8 years 1 month ago - 8 years 1 month ago #486 by firecoke
Replied by firecoke on topic Input/ Output Stages
:pedalboss: Hello I would ask for the resistors in series with the capacitor and 3v3 , is used paragraph How to use UN reference voltage at the operational amplifier But my question is this is the diagram is Necessary USE 3v3 in this reference ? which is the reason ? if one USA UNO vref 3v3 in the integrated is maintained in those values? Integrated are already fed 5v +/- 10v total peak with a peak Connect GND ground reference would not be sufficient or this would make the integrated output voltage rise of more than 5v ? It's not enough to have 1N5817 diodes to send signal peaks to the source?
I ask this because I'm doing my own version of But I'm working with 12v and other integrated , thanks.
Congratulations for your work is incredible sound quality achieved.

www.electrosmash.com/images/tech/pedalsh...ield-esquematico.png

Please Log in to join the conversation.

8 years 1 month ago #487 by Ray
Replied by Ray on topic Input/ Output Stages
Hi,
The Arduino DUE ADCs input voltage is from 0 to 3.3V.
If you inject a signal lower than 0V or higher than 3.3V you could damage the ADCs, this is why the clamp diodes 1N5817 are placed.
The guitar signal needs a "virtual ground" of 1.65V (3.3V/2). The sound signal will "float" above and below 1.65V and the ADCs will read it without problems.

Please Log in to join the conversation.

Time to create page: 0.083 seconds
Powered by Kunena Forum
Joomla SEF URLs by Artio

Follow us

You can also follow us on:

facebook   google   instagram

pinterest   youtube   twitter