DC-DC Step down modified for accuracy
Recently I have used the XM1584 small slim profile dc-dc step down converters for some small fan controls. The size means I can put it beside the fan and simply attach a power supply and done - variable fan speed control. However they are not very accurate because the potentiometer is not good.
Best part? They cost $0.50 in small quantities. Aliexpress link
The slim profile made it great for an outdoor (but enclosed) project for monitoring an animal habitat with an arduino and an esp8266 because of the slim profile. The problem was trying to tune the potentiometer to put out 5v. It was almost impossible. I could get it to 4.7v and 5.5v but not closer.
It is so sensitive, a small jerk of the screw driver would change the voltage by 0.5v
For this situation I decided to modify it with a multi turn hiqh accuracy pot. It was easy and worked great.
Later I used a smaller range pot with a resistor to modify a unit to supply 3v-6v with great accuracy.