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Introduction This application note is based on a few messages from the ADB I/O discussion list. For reference please look at Keelan Lightfoot application note. What Keelan shows is a H-bridge for controlling a DC motor in both directions from a single supply. This circuit is made with individual standard digital ICs. Here we propose a simpler interface using a single chip and only few external components. The chip includes the logic control and the output power transistors. This circuit can drive any DC motor up to 46 Volts, 2 Amperes and is controlled by two or three channels of the ADB I/O. Basically there are two ways to drive a DC motor in both directions. One uses two switches and a double power supply (Fig. 1.a). The second one is the H-bridge which uses a single power supply and four switches (Fig. 1.b). In both cases some logic is needed to ensure that both switches on one side are never closed at the same time. 
Fig. 1. The H-bridge allows to run a DC
motor in both directions with a single supply. The L298 (SGS-Thomson) and LM18298 (National semiconductors) are ICs which are essentially the electronic counterparts of the H-bridge of Fig. 1.b. The interface circuit The DC-motor interface described here (Fig.2) uses the L298 IC with four protecting diodes, one voltage regulator, 2 capacitors and optionally 2 resistors.
Fig. 2. The L298 H-bridge IC as an
electronic interface between ADB I/O and a DC motor. Click
on the figure to see details.
The control is through pin 10 (clockwise) and pin 12 (counter clockwise). An additional feature of the IC is that it is possible to control the braking of the motor through pin 11. When pin 11 is LOW (or not connected) the motor will slow down on its mechanical friction only. When it is HIGH (+5V) an electrical fast braking occurs. The braking mode can be controlled either by software through Channel 3 or permanently by the Jumper J (J must be closed when soft braking control is disabled). Connection to ADB I/O This DC-motor control interface can be connected either to port A or port B of the ADB I/O. The simplest way is through port B (Fig. 3.b) In that case, due to the TTL compatibility of the ADB I/O outputs and L298 inputs, the two resistors R can be omitted. The interface can be connected to Port A as well (Fig. 3.a). Some additional wiring on the output side of the ADB I/O is needed to bring the +5V to the relays contacts. In that case the two resistors R may be necessary to bring the inputs to LOW when the relays are open.
Fig. 3. Connection diagram of the
electronic interface to the ADB I/O ports A and
B. References: The most easy-to-find IC is the L298 from SGS-Thomson There is an equivalence from National Semiconductor:
LM18298 Somewhat similar devices are LM18200, LM18201, LM18245. Daniel Petitgrand petitg@llb.saclay.cea.fr |
| Note: The ADB I/O is no longer made or sold. These ADB I/O pages are hosted by Kaj Bjorkman as a favor to Sven Grenander (the founder and former Head Drone of BeeHive Technologies, Inc.)
Please let other ADB I/O users know that these archival pages are again available. |
