I originally used a buck converter to step down the 12v battery to 3v, but it failed and ended up draining the battery. I think for safety sake I want to keep the batteries separate.
I’ll take some pictures when I make the next one.
Plastic Project Box – https://www.amazon.com/dp/B003A67F90/ref=cm_sw_r_cp_api_ryYTybZ9YV4KC
5 Pcs Battery Box Holder w Cap On/Off https://www.amazon.com/dp/B00S4YIR4A/ref=cm_sw_r_cp_apip_5AndmDeI9KP8j
Previously I used these buck converters but after one failed I think I’ll stick to a direct 3v battery
Buck Converter 24V To 12v 9V 5V 3V https://www.amazon.com/dp/B018JWCX8M/ref=cm_sw_r_cp_apip_oVXzea8Ypccx1
Maybe something like this would be more stable but I haven’t tried it, and after the buck converters failed I feel safer with the AA cell.
SMAKN® DC/DC Converter 12V Step Down to 3V/3A Power Supply Module https://www.amazon.com/dp/B00ODL140M/ref=cm_sw_r_cp_api_kEYTybVB70XMZ