Servo motors feature a standard 3 pin connector that most often requires GND, 5V and 'signal'; in that order. So to make things convenient, tester needs to feature a single 3-pin output that matches.
One of the pins is power output, which often implies there's a power input, too. Servos aren't too picky about their input but ~5V seems to be the safe area for keeping the magic smoke from appearing.
And finally, there's the signal output. Consulting the datasheet for a Futaba S3003 servo motor, signal is described as the pulse of a certain width at around 50Hz (20ms). By varying the pulse width, between 1 and 2ms (or 2.5% and 5% duty cycle) the position of the shaft changes between roughly -90 and 90 deg.
So the above can be summarized to a couple of bullet points:
- 3-pin output (GND, 5V and 'signal')
- 2 pin input (some kind of voltage, higher or equal to 5V)
- Buck converter to drop voltage higher than 6(ish?) volts to 5
- PWM generator fixed to 50Hz, with 1.5 +/-0.5ms pulse width
- both buck/boost in one to support a wider range of input voltages
"Now hold on, what's the big deal here?" you might ask, "PWM generator with NE555 is nothing special and buck/boost module can be bought online relatively cheap".
Well, the idea is to to build everything up from scratch using NE555 in both the PWM stage, but also a buck(/boost) converter as the driver ^^ Then we can hopefully qualify to the 555 Timer contest. NE555 is truly an awesome little chip! It happens to be the first IC I touched when starting up with electronics and so I thought it would be fun to revisit the basics again...