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508 kaklik 1
EQ6 Mount controller analysis (v1 - 10 Jan 2004)
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Darren Hutchinson
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dbh@gbdt.com.au
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$Id: eq6-mnt.txt,v 1.3 2004/03/07 07:44:59 dbh Exp $
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Overview:
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CPU:		AT87F51
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Clock speed:	3.52 MHz (measured at pin 18 of CPU)
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Firmware:	MotorDrive DW3505010
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RA connector
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1	RA coil A	Driven RA=2,8,16x
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2	RA coil C	Driven RA=2,8,16x
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3	RA coil A	Driven RA=1x, 22R to 1, 178R to 4
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4	RA coli B	Driven RA=Any, 157R to 1, 178R to 3
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5	RA coil C	Driven RA=1x 173R to 6, 155R to 2
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6	RA coil D	Driven RA=Any 173R to 5, 22R to 2
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DEC connector
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1	DEC coil A	A/B are coil with 16R3 resistance
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2	DEC coil B
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3	DEC coil C	C/D are coil with 16R3 resistance
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4	DEC coil D
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Drive waveforms:
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RA 0X:	Coils not driven
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RA 1X:	Driven +12V for 114 ms, 0V for 114 ms, not driven for 38ms b/w
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	driven states, overall time is 302ms [OSC only accurate to 2ms]
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	Each coil driven at 90deg to other coil.
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	Timing correct for half step mode
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RA 2X:	Driven +12V for 75ms, 0V for 76ms, overall time is 151 ms, each coil
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	at 90deg to other coil
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RA 8X:	Overall period is 38ms, no undriven time, 
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	coils at 90deg
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RA 16X: Overall period is 12.8 ms, no undriven time, coils at 90deg
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- Timing indicates full step mode
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- No evidence of velocity ramp in x2, x8, x16 mode
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- RA 1X timinig is correct assuming 180 tooth worm and 1:132 transfer gear
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  & gearbox reduction ratio
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DEC 0X:	Outputs not driven
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DEC 2X: Overall period 151 ms, no undriven time
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DEC 8X:	Overall period 37.8ms, no undriven time, coils at 90 deg
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DEC 16X: Overall period 12.6ms, no undriven time, coils at 90 deg
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- Timing indicates full step mode
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- No evidence of velocity ramp in x16, x8, or x2 mode
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Drive circuit:
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The drive circuit is a fairly plain "H" driver with one quirk that may, or
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may not, be intentional design from Synta.
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The half-"H" is built from a pair on PNP/NPN transistors operating in
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common-emitter mode. This is somewhat unusual as circuits intended to
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drive high currents typically operate in common collector mode.
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Anyway, the PNP transistor that pulls the output high has a base current of
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about 11 mA (depending on the supply voltage). With a transistor hfe of
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40 this should give an output current of at least 500 mA.
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The other part of the bridge is another issue. The identical circuit is used to
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drive the base of this NPN transistor, but in this case it will only give
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the transistor 1.2 mA, leading to a lower current. 
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The rated hfe of the transistor only guarantees a current of about 50 mA, but
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the hfe is typically much higher. In the unit measured the coil current seemed
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to be limited to about 250 mA.
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This may be an attempt to limit the current in fault conditions where
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both the NPN and PNP transistors are active, or it may just be bad circuit
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design.
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In any case there are two practical effects:
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First the transistor may not be saturated, so it will run hot.
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Second the coil current is limited, giving less torque.
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Both of these effect mean that the existing electronics would be
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a poor choice as the basis of a GOTO design (but I guess you knew
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that ....)
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MCU Pin	Label	Use
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1	P1.0	1 = RA at 1x, 0 = RA != 1x
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2	P1.1	Same as P1.0
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3	P1.2	Same as P1.0
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4	P1.3	Same as P1.0
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5	P1.4	Same as P1.0 but connected to relay (1 = relay off, 0 = on)
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6	P1.5	Same as P1.0
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7	P1.6	Same as P1.0
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8	P1.7	Same as P1.0
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9	RST	R/C reset circuit, C = 22uF, R = 5K1, active high
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10	RXD	Data from controller via 1K resistor
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11	TXD	No data
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12	INT0	0V
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13	INT1	+5V
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14	T0	+5V
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15	T1	+5V
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16	*WR	+5V
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17	*RD	+5V
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18	XTAL	xtal out (freq meas point)
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19	XTAL	Xtal in
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20	GND	0V
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21	P2.0	1 = RA coil A to +12v, 0 = No effect
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22	P2.1	1 = RA coil B to +12v , 0 = No effect
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23	P2.2	1 = RA coil C to +12v , 0 = No effect
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24	P2.3	1 = RA coil D to +12v, 0 = No effect
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25	P2.4	1 = DEC coil A to +12v, 0 = No effect
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26	P2.5	1 = DEC coil B to +12v, 0 = No effect
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27	P2.6	1 = DEC coil C to +12v, 0 = No effect
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28	P2.7	1 = DEC coil D to +12v, 0 = No effect
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29	*PSEN	+5V
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30	ALE	Toggle at 602 KHz (high 540 ns, low 1.1 us) [~6 clk / ALE ]
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31	*EA	+5V
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32	P0.7	1 = No effect, 0 = RA coil A to 0V
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33	P0.6	1 = No effect, 0 = RA coil B to 0V
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34	P0.5	1 = No effect, 0 = RA coil C to 0V
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35	P0.4	1 = No effect, 0 = RA coil D to 0V
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36	P0.3	1 = No effect, 0 = DEC coil A to 0V
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37	P0.2	1 = No effect, 0 = DEC coil B to 0V
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38	P0.1	1 = No effect, 0 = DEC coil C to 0V
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39	P0.0	1 = No effect, 0 = DEC coil D to 0V
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40	Vcc	+5V
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Controller connector port:
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Pin numbers from RIGHT looking into socket with tab up (as numbered on
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controller board)
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1:	Switched +12V from hand controller
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2:	Ground
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3:	Data from hand controller via 1K resistor
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4:	Short to pin 1	
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5:	+12V from source via diode
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6:	Short to pin 5
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Notes:
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- Northern hemisphere selected during measurements
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- Relay is 5V, but appears to be driven via a resistor from the 12V supply
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- Finder LED has buffering (Q2)
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- Controller is series diode protected from reverse power connection
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Mechanical details:
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14mm from PCB to inside of cover plate
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5mm from PCB to top of MCU socket
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9mm from PCB to top of MCU