current requirements

current requirements of the hitec servos chosen for neck movement and mouth were found from manufacturer’s data sheets (see data sheets section)

current requirements of the cirrus servos supplied with the eye assembly could not be found from the manufacturer and were estimated from a hitec servo with similar torque output

this gave total servo current requirements as follows:

Servo	Current (mA)	Voltage (v)
eye pitch	280	4.8 – 6
left eye yaw	280	4.8 – 6
right eye yaw	280	4.8 – 6
left eyelid	280	4.8 - 6
right eyelid	280	4.8 - 6
neck yaw	700	4.8 - 6
neck top pitch	300	4.8 - 6
neck bottom pitch	300	4.8 - 6
mouth	180	4.8 - 6
total	2880

on request seetron quoted a 4 amp rating for the mini ssc servo controller board

current requirements for other electrical components were as follows:

component	current (ma)	voltage (v)
mini ssc	10	7 - 15
autotalk	20	5 - 6
camera (2)	100	6 - 12
pir (2)	24	7.5 - 12
total	154

interference

initial tests running the eye mechanism and the cameras concurrently showed that servo movement caused interference on the camera signal
experiments showed that using a secondary power supply for the cameras avoided this problem
although the cameras are specified as requiring 12v they run perfectly well at voltages down to 7.5v
this also allowed one power supply to be run at 6v for the servos and and one at 7.5v for the cameras and all other components

power supplies

the maximum theoretical current requirement for the servos calculated above is 2.9a
in practice the servos are not powered simultaneously so the power supply only has to be large enough to power the largest servo with a safety margin
following recommendations in seetron user manual two 1.2a linear regulated power supplies were purchased from maplin, one running at 6v for the servos and one at 7.5v for the other electronic components

autotalk board

the mini ssc servo controller supplied with the eye assembly had three spare servo outputs which were required to run the neck servos
to avoid the need for a second servo controller an autotalk board was purchased from milford instruments which drives a servo motor in synchronisation with audio input
a data sheet for the autotalk board can be found in the data sheets section
one disadvantage of this board is that it cuts out any audio output from the computer so a set of dedicated amplified speakers was also bought from maplin
secondly the gain was insufficient to move the featherservo the required range

interface box

the interface box was designed to use different connectors for each unique signal to avoid any ambiguity when connecting to it
a schematic of the connections between the sockets is as follows:

relay box

the relay box is used optionally for unattended running
it uses a card from audon technologies which allows relays to be controlled from the parallel port
one of these relays is wired in series with the low voltage side of the motor power supply unit
the effect of this is that inkha's motors can be turned off under program control
the control system turns the motors off whenever inkha goes to sleep which saves them from burnout caused by continuous running

there are some security issues involved with controlling a parallel port under windows nt and later and a windows driver and code from sst was used to overcome this