Need help checking over schematic for Arduino Nano Audio Sequencer PCB

[TonyAme]

I am working on making a pcb for an Arduino Nano based audio sequencer synth, a modified version of what I found here: https://cassiopeia.hk/sequencer/

Could use some help checking it over, any mistakes, etc. The help is greatly appreciated. *Some weird things you might see are a polarity protection p-channel MOSFET. The board peripherals (pots, etc.) are powered by regulated 5V, however the Nano itself is powered by 9 volts tapped before the 5V reg chip. Also, I used two CdS photoresistors connected to on/off toggle switches which adds their resistive values to analog A0 and A6. The photoresistors are both wired from the analog input pins to GND, which works very well for me.

Also, the mono audio jack is not connected, since I wasn't sure of it's pinout when I ordered it. So I left it as unconnected with jumper connector headers, so I can wire it properly when assembling the board.

Sincere thanks for any help anyone could offer.
TonyAm

 

[rjenkinsgb]

A couple of bits:

The +5V for the pots should come from the Arduino 5V output - there are two possible problems with a separate power supply:

The measured value can drift, as the input is no longer ratiometric.

The Arduino inputs may be powered through the pots, causing damage.

Also, in two places you have the possibility of connecting a pot wiper to +5V. If that ever happens at a low setting on the pot, it's shorting the 5V to ground and also likely burn up the pot track.

Use the changeover switch to disconnect the wiper when it connects to power, or switch the pot ground to +5V, or add a series resistor (1K) between the pot wiper and its cap to eliminate the short possibility.



Also, I notice you have a 9V battery holder in there;
7V is the absolute minimum for a 7805 input.

A 9V can and will drop to 6V in use - use a low dropout regulator instead of the 7805, otherwise you will be endlessly discarding good batteries.

I don't really see anything that calls for a separate 5V supply? I'd just use the Nano 5V output and get rid of the separate regulator, it will simplify things and save power. It's rated for around 500mA and you should not need a fee tens of mA for the pots etc.

 

[TonyAme]

A 9V can and will drop to 6V in use - use a low dropout regulator instead of the 7805, otherwise you will be endlessly discarding good batteries.

I don't really see anything that calls for a separate 5V supply? I'd just use the Nano 5V output and get rid of the separate regulator, it will simplify things and save power. It's rated for around 500mA and you should not need a fee tens of mA for the pots etc.

I see, I'll have to go through this and consider your suggestions. The low dropout voltage is a great idea, or supplying straight from the Nano's 5V supply. Thank you for bringing those things to my attention.

Sincere Thanks!

 

[TonyAme]

Could you recommend a suitable low dropout regulator?

Thanks again,
TonyAme

 

[rjenkinsgb]

These are ideal for battery powered devices; very low dropout voltage and internal current consumption:

https://www.mouser.co.uk/ProductDetail/Microchip-Technology/TC1262-5.0VAB?qs=npqfqDPP3%2Fy2GSlQUA70qg%3D%3D

The built-in one in the Nano is also pretty good, a 1117 style LDO I believe.

Again, don't mix internal <> external supplies on anything directly connected to an MCU.

 

[TonyAme]

Thanks very much for your help on this. Very much appreciated.

TonyAme