The Power module shown in Figure 1 is built around four L272M integrated circuits: IC1-IC4. Each of them contains two powerful operational amplifiers with maximum output currents up to 1 A. These amplifiers are used to switch loads connected to their outputs, to the ground (pin 4) or to the positive power supply voltage (pin 2).

The inverting inputs of all amplifiers are connected to LED1, which provides them with a bias voltage of around 1.5 V. Non-inverting inputs are connected, via IDC10 connector PX and appropriate cable, to any I/O connector on MPIN (and from there to the I/O pins of the microcontroller). Logic levels on these pins determine the output states of the power amplifiers:

• logic Low (“0”) at any pin switches the corresponding output of IC1-IC4 to 0 V;
• logic High (“1”) at any pin switches the corresponding output of IC1-IC4 to the positive power supply voltage.

The Power module is connected to MPIN via a cable, as illustrated in Figure 2. A 10-wire flat cable, with 10-pin IDC10F connectors at both ends, is used. The preferred length of the cable is up to 50 cm, but even longer cables can be used in most applications. Be sure to orient the connectors as shown in Figure 2: equally marked pins should be interconnected (1-1, 2-2, etc.).

The cable connects the non-inverting inputs of the Power module to the pins of the selected I/O port, as well as the ground planes of both devices, and provides the positive voltage supply from MPIN to the Power module. This voltage (+5 V or +3.3 V) is used only for LED1 - the Power module requires its own power supply. The output voltage of this supply should be selected according to the requirements of the loads connected to the M0-M7 output terminals. You must allow for a 0.5-1.5 voltage drop within driver ICs IC1-IC4, depending upon the load current and the way in which the loads are connected - see the L272M data-sheet. The output voltage should be stable (but it does not have to be regulated) and the power rating depends upon the sum of the maximum currents through all connected loads.

Figure 3 shows how to connect the Power module to MPIN development boord. Although PORTD is used for this connection, any one of PORTA-PORTD connectors on MiniPin II or PORTA-PORTF on MegaPin can be used. Of course, which ports can actually be used depends upon the installed microcontroller and other devices (switches, 1-wire components etc.) that may already be connected to some of the I/O pins. In the following text, we will assume that PORTD is used, but the same applies to the other I/O ports as well. You can even connect two or more Power modules to one MPIN, as long as you have enough free ports.

Driving motors with AVR

2012_AVR_UK_45

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