Digital display for DIY 25W dummy load – part 4

Digital display for DIY 25W dummy load – part 1 described a  digital display for a DIY 25W dummy load / digital wattmeter. The original research tested implementations on an Arduino Nano (ATmega328P) and Arduino Mini Zero (ATSAMD21). Though the Zero appears the better chip (32bits, better ADC resolution etc), the dev board is so noisy (ADC wise) that the Nano produces better results.

Other candidate chips are those of the newer AVR chips, and to that end some ATtiny1614 chips were purchased for trial. Unfortunately I have not seen inexpensive dev boards and the chips are not available in DIP format, these are SOIC14 (SSOP14) 150mils.

Above is the result of this morning's cooking… three ATtiny1614 chips on DIP style break out boards for prototyping. The chips were soldered in a T962 IR reflow oven. The very long unmasked sections of pad to accommodate different width chips make for a messy looking solder job as the solder runs along the long pads.

So, notable differences:

  • these have improved ADC (still 10 bit, but potentially better noise performance);
  • UPDI programming interface (one wire + ground); and
  • better debug..

They have EEPROM (256B), so implementation of my preferred scheme of calibration constants in EEPROM is as easy as any of the older AVR chips.

But the bigger question is whether the code will fit in 16kB of flash, it might be ok.

A similar run of some ATtiny816 chips. The same thing will be done with some ATtiny3216 when they become available again.


The code as it exists at this moment is just a little too large for a 16kB flash chip (ATtiny16xx). The ATtiny3217 has sufficient memory, but only available in a VQFN24 package so not so easy to find inexpensive break out boards… maybe in time. The ATtiny3216 (SOIC20) has promise , but scarce… though I will try to source some.