F1..F4: these are FET switches capable of up to 2A; they are open circuit when off and connected
to battery negative when on; a load should be wired between the F pad and battery positive, or
the 3.3V pad for low current loads; labelled A..D on the receiver board and numbered 7..10 for
The power input and motor output pads have a 3.5mm spacing which allows use of a screw terminal
(optionally available when MR603 is purchased). The long side pad spacing is 2.54mm which allows a
pin header to be attached if plug connectors are preferred for the F and P outputs. A JST-SH 4 pin
socket may optionally be fitted for P5, P6, 3.3V and 0V.
LEDs on P pads should be connected between the pad and battery negative (0V) with a series resistor
appropriate to the required brightness. P1 to P4 have a series 180 ohm resistor on the PCB, P5 and P6
have no resistor. LEDs or incandescent lamps on F pads should be connected between the pad and
battery positive or the 3.3V pad and with a series resistor appropriate to the voltage and required
brightness.
Sound card inputs are usually 5V open circuit and are triggered when connected to negative. They
should be connected to an F pad. A P pad may be used if you have more trigger inputs than F pads, or
a P to F converter is available from Micron - this is a small board containing 1, 2, 3 or 6 FET switches.
If the P output is used directly for sound card trigger, a 4k7 ohms resistor must be connected in series
to avoid stressing the MR603 microprocessor; the P output should be configured for 3.3V idle and 0V
when the Tx control is actioned.
Take care when soldering wires to P1..P4 and F1..F4 (A..D) as the pads are very close the radio sub-
board. The recommended technique is to fill the pad hole with solder and then attach the wire to the
top of the pad on the side opposite to the radio board - i.e. don't pass the wire through the pad hole.
Low Voltage Cutoff
MR603 can be powered from a battery of 5V up to 20V. The speed controller will stop the motor if the
battery drops below 5V but the other receiver functions will continue to operate down to 4V.
The default receiver setting is for the Low Voltage Cutoff (LVC) threshold to be determined from the
voltage measured at switch on. This is auto mode which is essential when the receiver is powered
using a Lithium battery (LiPo or LiIon) as these must not be discharged below 3V per cell. The
algorithm used for this calculation means that a 9V Alkaline or NIMH battery can often be interpreted
as an almost discharged 3S LiPo. The solution is to either disable LVC, or set it to the correct value for
your battery. Switching between auto and disabled can be done using a
and the LVC threshold can be set to a specific value by
the receiver.
Indicators
MR603 has 2 LED indicators, one on the top near the aerial and another on the bottom, these are
labeled 'RF LED' and 'CPU LED' on the diagram:
RF LED:
lights continuously when a good signal is received, flashes rapidly when the receiver is in bind
mode and flashes intermittently if signal is poor (transmitter too close causing overload or
transmitter too far away)
CPU LED:
indicates the receiver status:
immediately after switch on, emits a 0.5s rapid flash followed by a flash pattern to show the
active configuration (1..4), repeated once: e.g. rapid-flash, pause, 2-flash, pause 2-flash
shows that the receiver is using configuration #2
flashes slowly while waiting for a good transmitter signal
lights continously when a good R/C data is being decoded
Micron R/C, www.micronradiocontrol.co.uk, +44 (0)1653 696008
Micron MR603b 2.4GHz DSM2/DSMX Receiver : 3 of 10
