Components sourcing list
PCB : JLCPCB $2 for 5 pcs ,now JLCPCB provide 4 layers sample by $5!!!
Components: LCSC around $1
1 Developed according to 51 SCM of STC15W104 series.
2 Using the power off mode of STC51 microcontroller, the power consumption is very small when not working (the working area is less than 25uA)
3 Big button, easy to operate.
4 Default setting is 6 minutes, can be modified.
5 At the end of the timer, the buzzer will sound at full volume for 40 seconds (which can be modified in the code).
6 Pressing RST button is time reset, and pressing STOP at any time can STOP the buzzer ringing.
7 It has a working indicator light provide instructions when working.
8 It has a low power indicator to indicate when the battery level is below 3.3v.
The first sample by a breadboard looks like the below picture;
For further manufacture ,Enclosed the Diagram Schematic;quite simple;