I want to build Scullcom's millivolt meter: http://www.scullcom.uk/millivolt-meter-mk2/ , but can I use an atmega328 instead of the pro mini or nano? If not, any through hole microcontrollers I can use?

 

Really nice project.
Millivolt Meter Version 2 - Barbouri's Electronics Projects
Atmega328 fully functional ?

The 24 bit LTC2400 Alpha Sigma ADC connected to a PC almost got 6 place accuracy was software capable.

 

Arduino's are a great uProcessor learning tool. But the real point is to learn to use the uProcessor without all of the supplementary support devices on the development board. Yes, you can use a standalone uProcessor! And the Arduino IDE supports that. Time to take the "water wings" off and go solo! Which one you use depends on your circuit and how many uProcessor pins are needed to support it.

 

Yes, you can use the ATmega328-P for that project. You will need a 16MHz crystal and a couple of 22pF capacitors. Just make sure that you match the input and output pins correctly. I did not unzip the schematic diagram so I don't know how the power supply is wired to the arduino board. You may have to add a 5V regulator for the microcontroller.
There are posts on the internet that show how to program the chip using an uno.

 

Hey! Don’t forget power supply bypassing and a resistor to pull-up the reset input.

 

If you use an ATmega328 and want to program it in situ on your final board then you will need to provide connections on your board to do that. An alternative way is just to program the chip when it's plugged into an Uno (the type where a through hole chip is plugged into the socket on the Uno) then remove it from the Uno and plug it into your board. This should be fine so long as you don't wear out the socket on the Uno.

 

You can indeed use the processor. Many of my industrial control products use various PIC processors. But I find the Arduino is a good "component" in itself. I can buy an Arduino Nano (or Pro Mini) for probably less than the processor, crystal, regulator and other Rs and Cs needed to make it all work. I have used Pro Minis in a product just like that, as well as Arduino Nanos in many Ham radio VFOs and controllers. Also, you are starting with a proven working device, not something you have to debug.
So, I think it is quite valid to use an Arduino. I have noticed there are those on this forum that seem to look down on the Arduinos and I do find that odd in that if you use the exact same parts on a custom board, then it is ok. Very odd indeed!

 

I have noticed there are those on this forum that seem to look down on the Arduinos

While it's indeed true that there are better/faster MCU than the 8-bit ATMEL/Microchip AT products (eg 32-bit ESP32 & STM32), for many projects the AT range are perfectly useful at 8MHz internal clock or 16/'20MHz external clock/crystal. The ATtiny 8/14 and 20pin devices with 8MHz (factory calibrated internal clock) are great for industrial control/sequencing purposes. My current preference is the ATtiny87 which are under a £1/$1 in a SOIC20 package for 1.8 - 5v operation, great for battery powered projects and, like the 28pin ATmega328, can programmed in-situ with an Arduino UNO/Nano or a dedicated $5 USBasp programmer from the Arduino IDE. My only issue with using an Arduino UNO or even a Nano is their massive footprint compared to the bare chip which usually is all that's needed in most custom situations.

Incidentally, if 8MHz is too slow, I prefer a 4-pin 16MHz oscillator driving the ATxxxx X1 pin rather than a 2-pin crystal or resonator and 15/18/20/22pF capacitors as some crystals are reluctant to oscillate reliably without the correct capacitor combo an it can be a pain sorting it out on-board later. The cost is broadly similar.

 

Yes, I have even used the base 12F629 PICs quite well too for a couple of products. A custom light bar flasher and a CTCSS tone generator for Ham radios.Quite a step down from the DSPIC and PIC32 boards I've produced. But, sometimes the small base level parts are quite ok.

 

Microchip has released some newer Unified Program and Debug Interface (one pin) programmable SMD chips. With internal 20MHz clocks, lots of memory and 8/14/20 pins. Take a look at the ATtiny214/414/814 chips. ATtiny212/214/412/414/416 (microchip.com) You can always put one on an SMD adapter board for thru hole use.

 

Take a look at the ATtiny214/414/814 chips.

Yes, I've been looking at them. Just need to tweak my programmer to work with the 1-wire interface.

I particularly like the Custom Logic CCL which makes up for the smaller Flash (only 2 or 4k).