NuukiaWorld project:
FBUS & MBUS adapters

4. MBUS-only adapter

4.1 8-component MBUS-adapter

This chapter contains building instructions for NuukiaWorld's 8-component MBUS-only adapter based on the idea described in chapter 1. The circuit is almost the same as the 8-component FBUS-only adapter, so you should check also the information on that page.

This adapter may be used with all Nokia phones with MBUS. The voltage level of the phone is not a problem, so this circuit is useful also with older phones than the Nokia 5110/6110 series. For simplicity, this page uses the pin outs of the Nokia 5100/6100 series GSM phones. You must find out the correct pin numbers of the phone by yourself, if you are going to use another phone model.

Note: The Nokia Data SuiteTM application uses only the FBUS transmission method. If you are building an extra cable for your NDS, please prefer the FBUS-only circuit.

Figure 4.1 NuukiaWorld's MBUS-only adapter using MAX 232.

Table 4.1 Required components for NuukiaWorld's 8-component MBUS adapter.




Price* ()


Emergency solution***

U1 1 MAX232 0.69 Other manufacturer's equivalent substitute (possibly all "232" chips are not equivalent with MAX232) MAX3232, requires pull-up to pin 10, smaller capacitors and zener diode. V+ must not exceed 7 volts.
  1 16 pin IC socket 0.30    
D2,D4 2 1N5819 0.94 Any schottky diode 1N4148
D3 1 4.7V 400mW zener 0.12 Any 4,7 volt zener with higher power rating 78L05-based linear regulator circuit
C1,C2,C3 3 1µF 16V 0.30 Any 1µF capacitor with higher voltage rating  
R1 1 47 ohm 0.05    
J1 1 DB9 female 0.34 DB25 female (different pin arrangement, see chapter 2.3)  
J2 1 Phone connector      
    Copper-striped circuit board 11 x 10 holes

Note: The "Price*" is an example price (that NuukiaWorld had to pay in Finland) for the total number of the component when bought one by one. Tax (VAT) is not included. Parts substitutes marked "Equivalent**" may be used in the circuit without any problems. Parts marked "Emergency solution***" are not recommended and may require other modifications to the circuit. These modifications require good knowledge in designing electronic circuits, may affect the reliability of the circuit, and such circuits are not tested by the NuukiaWorld. Try to avoid those components.

The adapter circuit consists of a standard MAX232 design with modified power supply part. See the 8-component FBUS-adapter description for details.

4.2 Building the MBUS-only adapter

The circuit is so simple that a printed circuit board is not required (see figure 4.2). The DB9 (female) connector is soldered directly on the edge of the board. (The five pins of the connector shown in figure 4.2 are on the copper side of the board. The board is pushed into the gap between soldering lugs 1...5 and 6...9 of the connector.) The pin 7 (RTS) is soldered directly to the anode of the D2. Remember to short-circuit pins 1 and 2 of the connector as shown in figure 4.2.

Figure 4.2 Circuit board layout for copper-striped board (component side).

The capacitors could be almost any kind according to Maxim, and I used 1 µF 35 V tantalum ones because of their small size. The voltage rating of 16 volts is enough. The two diodes in the circuit are schottky ones to avoid unnecessary voltage drop.

Use an IC socket for MAX232. Please note that in the circuit board layout shown in the figure 4.2 the pins 1, 3, 11, and 14 of the IC socket must be cut away.

4.3 Testing the MBUS-only circuit

The testing of this MBUS adapter is similar to the testing of the FBUS-only adapter. See chapter 3 for details. Do not connect the phone to the adapter before all tests are passed. In the loop-back test Tx & Rx lines must not be connected together (because they are already together in an MBUS adapter).

If you do not get the correct results in the measurements, there is a failure in your circuit. Check the circuit carefully and retry the tests.

- © Copyright 1998, 1999 Panu M Tuominen. All rights reserved. Republishing this document partially or completely is forbidden. Internet hyperlinks to the main page are allowed and such linking is encouraged. You are doing everything at your own risk. See the WARNING! in the general information page.

The basic tests have been done with the Nokia Data SuiteTM 2.0 and Nokia Data SuiteTM 3.0, Nokia Logo Express, LogoManager demo version, a Nokia 5110, a Nokia 6110, a Nokia 6130 and a Nokia 6150.

21.5.2001 - nuukiaworld@gmail.com
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