Schematic: https://oshwlab.com/speed/dc-speed-control

Keep in mind, this is rework of https://hackaday.io/project/166492-grinder-speed-control-with-stable-rpm. Many things are very similar. Let's describe difference.

MCU

Currently, many chips become not accessible (very high priced). MCU is changed to  STM32G030F6P6. It has no USB support (no easy flash without programmer), but has low price and better performance.

Appropriate components, related to USB uploader, are removed. Also, removed ADC power filter, because new MCU usees the same pins for digital & analog power.

Motor's commutator

For FFT-based frequency detector we need PWM instead of phase control. So, instead of triac we use rectifier + mosfet + anti-spike diode.

• Cost is comparable.
• Thermal loss is similar.
• Size is a bit more high (due rectifier), but not significantly.

Note, most of brushed motors (without magnets) are "universal". That means, those works well with both AC and DC power. In theory, those need some correction of winding count for DC power. But in real world, those work "as is".

Current sensing shunt amplifier

Since FFT-based algorithms are well resistant to noise and DC drifts, shunt amplifier is replaced with INA180A2IDBVR - more cheap and more easy to mount.

AC-DC power

Schematic is the same, but step down output increased to 5.5 volts for more stable mosfet control. Also, LDO replaced with more simple, supporting 6 volts input.

Voltage sensor

FFT frequency detector requires only value of current to work. No voltage sensor needed. Appropriate components are removed.

Other advantages

New regulator should be very flexible. For example:

• Can be used to control 110 volt AC/DC brushed motors from 220 volts AC.
• Can be used for DC low voltage tools. Just remove rectifier, step down converter and replace switch component for appropriate voltage/current.