This is Jimmy mounted on his plinth as a trial assembly.
He is stood on a turntable which is driven by the servo.
A three volt cell was plenty to drive the motor and it took an acceptable 50mA.
This test helps me to design the servo current limiter.
Electronic circuit design was a major task. Here you can see several sheets of
circuit diagram being converted into a board layout plan.
There were a lot of electronic components to order. This pic shows some of the
components ranged about the workspace ready to begin circuit board assembly.
Jimmy and new Friends
Jimmy makes friends with the mice, soon to be used as training aids.
Jimmy on his new patch of grass
Ivor the postman brought a parcel for Jimmy today, it turned out to be his patch of grass.
This is a test of Jimmy's eyes to ensure they are operating properly before installation.
Sorry about the fire engines!
Testing the Optical Sensor and Amplifier
This is the most demanding task in the project. The optical sensor sees a lot of ambient light,
and this has to be rejected whilst applying a lot of gain so that the pulsed light can be sensed.
Optical Sensor Amplifier - Design Optimisation
The optical sensor amplifier had to be optimised for maximum gain and minimum phase,
whilst tolerating maximum ambient light without saturating.
The Jimmy project looks to be going well, so I've ordered a sound board kit,
to give him a voice.
Servo Test 1
This short vid shows the servo driving Jimmy to and fro, just to check the speed and total movement.
Stability seems ok, considering a tiny little model servo is turning quite a large crow, but at slow speed
there are a lot of notchy oscillations, possibly caused by the very crude emitter followers in the servo
amplifier output stages. Rather than go to the lengths of designing better circuits, I am going to try the
use of dither, which is a standard way of overcoming servo backlash and dead band problems.
Servo Test 2
I tried adding dither, which is a standard way of overcoming servo limit cycles and this worked,
but came with the penalty of a loud 1kHz sound from the motor. Then I brought some wires out
so I could experiment with gain settings. Reducing the loop gain from 100 down to 10 proved
Hurrah! Jimmy sees a White Mouse
Jimmy woke up this morning with the gift of vision! He can see a white mouse and follow it round,
he even turns to look as a human walks past. Hurrah for High Intensity LEDs!
Still a little bit twitchy, looks as though he has St Vitus Dance, need to work on the dc amplifier to
reduce the noise a bit. Then we have to fit the sound card so as to give him a voice.
Inside the Box
This is the innards of the box Jimmy stands on. Top left is the battery and on/off switch.
Top right is the main electronics board. Top R-L: oscillator, distribution buffer, led drivers.
Lower L-R: optical amplifier, ac amplifier, synchronous demodulator, dc amplifier, servo amplifier and motor drivers.
Centre is the Futaba servo containing motor, gears and feedback pot.
To the right of that is the sound card, purchased ready built, and lower centre is the speaker.
Jimmy in Training
Here is the final vid of Jimmy training to follow a white mouse.
Commentary by Jimmy himself.
PS - After analysis of the overall sero loop it was found that the twitchiness was caused by the odd few ms delay in the
synchronous detector. A remedy was tried but was not satisfactory. Any future similar project must take this into account.