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Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

LDR Pre MkII - LDR volume control and I/O switching
LDR Pre MkII - LDR volume control and I/O switching
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Old 15th March 2019, 04:28 PM   #11
zdr is offline zdr  Belgium
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Quote:
Originally Posted by md_Stryker View Post
ZDR,
Can you describe the hardware modifications required to the Arduino Nano with Atmega328PB for this project?

-Michael
There are modifications in IDE, in hardware and in bootloader. PB has two 16bit compare registers which overlap with RX/TX lines used in Nano, so I had to redirect serial1 to serial0 Nano pins and use serial1 instead of serial0. Forgive me that I do not remember exactly the pin names or everything I did exactly, it was done few months back. Bootloader had to be modified also to use serial1 for flashing instead of serial0.

Now that most of the parameters are exposed in the user interface, I would expect that most of the people would not care about open source and fiddling with Arduino IDE.
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Last edited by zdr; 15th March 2019 at 04:39 PM.
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Old 15th March 2019, 04:31 PM   #12
zdr is offline zdr  Belgium
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Quote:
Originally Posted by Theodosis O. View Post
Hi zdr,

What about to split the board in two ?
One board with relays and LDRs and maybe with I/O connectors
and the other with Arduino and control stuff and maybe with OLED display.

In this way you have the noisy stuff away from signal.
PCB layout took care of that. Grounds are separated and pierced all over with vias. I usually do not solve problem I cannot see, hear or measure, since it probably does not exist

I hate messy wiring between boards, I prefer it like this. It also keeps the cost down.
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Old 15th March 2019, 04:36 PM   #13
zdr is offline zdr  Belgium
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So far, I have the code pretty much ironed out for 2.4" graphic I2C oled from wide.hk. I was thinking in offering bare PCBs with modified, flashed and bootloaded Nano Clones for 25eur. If you want relays soldered in, add 30eur to the total. Shipping is 5 eur to almost anywhere.
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Old 15th March 2019, 04:44 PM   #14
zdr is offline zdr  Belgium
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The code actually runs DACs (PWMs) in 12bit resolution, although hardware has native 16-bit compare registers and timers. The reason for this, is that ADCs cannot "see" this resolution, and therefore it's would be a waste of resources - they are still 8-bit, software oversampled to 12-bit. 12-bit gives however a significant increase in precision compared to original 8 bit, eliminating the need for impedance range switching which was causing volume "bumps".
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Old 15th March 2019, 04:46 PM   #15
zdr is offline zdr  Belgium
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Quote:
Originally Posted by nori1000 View Post
How many inputs have the Board?

the preis is?

Put me on the list for two as well
I/O count has not changed - 4 inputs and 2 outputs.
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Old 15th March 2019, 04:48 PM   #16
zdr is offline zdr  Belgium
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Power supply PCB layout is pretty much the same as before, only the regulators and transformer specs were changed. Trafo is now 2x6V 10VA, all regulators are LM7805 or similar.
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Old 15th March 2019, 04:55 PM   #17
zdr is offline zdr  Belgium
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The code has been modified to be downstream power amp friendly:

1) Saved volume is capped to max value saved in the parameters, default 25. It cannot happen that device starts up at max volume level, unless you allowed it explicitly in the parameters.
2) Device boots in standby mode - all relays are switched off, LDRs placed in high resistance mode, OLED is showing only three dots. You power up the device by pressing and holding play button on the remote. You put it again in the standby the same way - three seconds press on play button.
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Last edited by zdr; 15th March 2019 at 05:03 PM.
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Old 15th March 2019, 05:01 PM   #18
zdr is offline zdr  Belgium
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Volume steps are one thing still not exposed in the user interface, I have doubts about it. In order to do so, I would have to reserve dynamic memory for an array sized for max steps, which is 80 or even 100, even though most of us will use 50 most of the time. After adding full remote control operation in the code, I'm not sure there is still enough room for this in memory.
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Old 17th March 2019, 12:00 PM   #19
zdr is offline zdr  Belgium
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I've got 7 bare boards with patched nano clones and latest firmware ready to go, for first seven PMs in my inbox Price is 25eur plus 5eur shipping for early adopters. If you want relays bolted in, add 30eur.
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Old 17th March 2019, 12:03 PM   #20
rpafenberg is offline rpafenberg  United States
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I'll take two, what about the new power supply boards, still 5eur
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