
OG_MU-4-434_v10e Circuit Design, Inc.
13
OPERATION GUIDE
Chapter 3 How to Design a User System
3.1 Circuit Board Design
When embedding this unit in a user system, pay due attention to the design of the board and case.
1. The power supply used for the MU-4 must be a DC regulated power source, with a voltage span of +3.0 v to
+5.0 v. A current of about 40 mA is required when transmitting. Ensure that the voltage of the MU-4 and user
system CPU are the same.
Although a regulated voltage is supplied to the internal high frequency component, in order to support the
voltages of a variety of user systems, the power supply for the CPU is connected directly to the VCC terminal.
For this reason, care is required to achieve the correct voltage range.
2. Add a 1 kΩ resistor or 0.33 μH inductor to the UART related control signal line. This should be inserted close to
the connector pins.
3. When attaching this unit to a circuit board, use a double sided circuit board if possible. On the top surface of the
board, make a sufficient area beneath the MU-4 for the ground pattern (GND plane), and use the bottom surface
of the board for signal lines.
4. If the MU-4 power supply line is used jointly with the power supply lines of other circuits in the system (such as
the CPU), it may cause malfunctions, and the unit may not perform properly.
For the power supply of the MU-4, always use a separate line from the system power circuit, and install bypass
capacitors at the receiving point.
5. It is possible to directly connect LEDs to the LED terminals, however ensure that the LED current is limited to 1
mA or less.
Blinking of the LEDs may affect communication. It is recommend that ceramic capacitors of about 100 pF are
added in parallel to the LEDs.
6. Do not connect anything to RXM terminal.
7. Make the signal lines to this unit as short as possible.
RXD
TXD
CTS(Port)
RTS(Port)
Port
DC +3.0v to +
5.
0v
+
-
+
3.
0v to +
5.
0v
1k
Ω
220
μF
470 pF
470 pF
VCC
GND
470 pF
To user parts
To user parts
GND plane
MU
-4
Antenna
TXD 1
RXD 2
RTS 3
CTS 4
MOD 5
INI 6
RST 7
RXM 8
RF
14 GND
13 VCC
12 RXL
11 TXL
10 DO
9 DI
User CPU
With UART
Peripheral
Regulator
DC Power
Tx,Rx Indicator