My new preamp design: Arduino, 6 input selector, MDAC attenuator, IR etc

[stocktrader200]

that chip looks really good. Arduino control is great. My setup is not well suited as I am using a twin triode 6922 setup with the first stage driving the 100k pot with loudness function. The second 6922 drives the tone stack which then drives the SS amp.
Great looking preamp!!
input LEDS or LCD in the centre of wheel would indicate which input is selected and volume level expressed as -Db

[zgtc]

Hi Max, again pretty nice project. I'm about to request the BOM to complete the input selector board, and have a (stupid) question.

I understand the MCP23S17 serves as a SPI expander, so we can use the SPI line between an Arduino and more than one sensor or IC.

What I'm not so clear about is the ULN2003V12DR relay load drivers. Since these support 3.3V to 5V CMOS logic input interface, wouldn't it be possible to send those signals from the MCP23S17 or Arduino directly? I mean, the latching relays just need a pulse, right?

Sorry, I know these are stupid questions, but would love to learn more.

Thank you

[maxw]

Originally Posted by zgtc

Sorry, I know these are stupid questions, but would love to learn more.

No such thing

Originally Posted by zgtc

I understand the MCP23S17 serves as a SPI expander, so we can use the SPI line between an Arduino and more than one sensor or IC.

Correct.

Originally Posted by zgtc

What I'm not so clear about is the ULN2003V12DR relay load drivers. Since these support 3.3V to 5V CMOS logic input interface, wouldn't it be possible to send those signals from the MCP23S17

To quote the datasheet:

> Internal Free-Wheeling Diodes for Inductive Kick-Back Protection

If you don't have these then you will need a diode across each relay coil.

Originally Posted by zgtc

or Arduino directly? I mean, the latching relays just need a pulse, right?

Sure but then you need many free pins on the micro controller. 2 per relay. And depending on what controller you are using, you might not have that many free pins. That's why IMO it's nicer to use SPI.

[zgtc]

Originally Posted by maxw

No such thing

cool

Originally Posted by maxw

Correct.



To quote the datasheet:

> Internal Free-Wheeling Diodes for Inductive Kick-Back Protection

If you don't have these then you will need a diode across each relay coil.



Sure but then you need many free pins on the micro controller. 2 per relay. And depending on what controller you are using, you might not have that many free pins. That's why IMO it's nicer to use SPI.

OK, I wasn't conceptually far, then!

Now, a not-stupid, just maybe weird scenario/question. Would it be possible to use the input selector to switch audio signals and also close/open power circuits? Changing the arduino code, maybe even changing the pcb design, that is. Example situation: relay 1 for phono audio, relay 2 for phono amp power circuit, relay 3 for dac audio, relay 4 for dac power circuit, relay 5 for aux audio. If this is conceptually possible, i would be able to only power the phone amp or the dac when i select those specific audio signals

[zgtc]

As for the last question, maybe if switching power circuits is not supported by this design (even if modified), then I need to look into "triggers", i.e. Signal Detecting Auto Power-On Unit (project 38) by Rod Elliott (ESP), but will obviously do some more research.

[maxw]

Originally Posted by zgtc

Would it be possible to use the input selector to switch audio signals and also close/open power circuits?

It won't work as it's designed as (6 input, 1 output) x2. Perhaps you could have voltage going in and then you can connect 6 devices to this bus. It might work for low voltage things but definitely not safe for mains voltage.

Personally I would look for another solution. You can get cheap relays that you can control with an Arduino from Aliexpess.

[zgtc]

Originally Posted by maxw

It won't work as it's designed as (6 input, 1 output) x2. Perhaps you could have voltage going in and then you can connect 6 devices to this bus. It might work for low voltage things but definitely not safe for mains voltage.

I think I'll keep the original use for the relays. Is it safe to leave 2 or 3 relays unpopulated?

Originally Posted by maxw

Personally I would look for another solution. You can get cheap relays that you can control with an Arduino from Aliexpess.

Hadn't thought of cheap relays, it's a nice idea. Thank you

[maxw]

Originally Posted by zgtc

Is it safe to leave 2 or 3 relays unpopulated?

Sure

[dayal]

Max you are a Genius

[zoidbergslo]

Wow Max. This project came a long way since your first version.


Looking at your new implementation and code I am tempted to redesign it for MCU running python.