Well, haven't do any real PCB designs for many years and trying to do it again (so don't expect too much about quality of the design).
The design is for point motor control in model railway, where the servo motor position need to be set to two configurable positions. There are commerical products available of course, but I think it worth doing my own just to refresh my knowledge in PCB designs.
The design have two PWM connectors, supporting two servo motors. I use SG90 for this experiment. It is design for 4.8v operation but can operate at 3v (but the movement is reduced in this low voltage).
There are 5 variable resistors for configuration:
- servo motor #0 position A,
- servo motor #0 position B,
- servo motor #1 position A,
- servo motor #1 position B,
- servo motor speed.
Two toggle switches are used to control the servo motor position selection.
I add a connector for a SPI LCD module for other experiments.
For the microcontroller, LPC1114FN28 is select as this is in DIP package (easy for makers to solder at home). In fact, all components I used for this design is through hole components to make it easier for inexperienced makers.
PCBs are back and working. But there are two issues:
1) I forgot to add a capacitor (0.1uF) for reset.
2) When a GS90 servo motor is connected to J8, the MCU doesn't boot up. That is because if PIO0_1 pulled low during reset the MCU onchip firmware will start the ISP command handler (see UM10398.pdf, section 26.3.1). So I need to modified the servo motor connection to get it working.