LM1872

Manufacturer Part NumberLM1872
DescriptionRadio Control Receiver/Decoder
ManufacturerNational Semiconductor
LM1872 datasheet
 


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Applications
(Continued)
BRIDGE DRIVING A MOTOR
The two digital channels can be used to propel a car for-
ward off and reverse without the need for a costly servo
(Figure 16) The 100 mA digital output capability is used to
drive a bridge of four transistors with Q5 added as a protec-
tion device Should an erroneous command to power both
sides of the bridge occur (as may happen due to noise with
the car out of range) the large motor drive transistors would
fight one another resulting in the thermal destruction of one
or more of those devices But Q5 will disable the left side of
the bridge whenever the right side is powered preventing
the problem from ever occurring The motor noise suppres-
sion network shown has proven to be especially effective in
reducing electrical noise and is therefore highly recom-
mended
NOISE INTEGRATION OF A DIGITAL CHANNEL
Commonly available inexpensive DC motors are a formida-
ble source of electromagnetic interference Radiation can
FIGURE 15 Interfacing Directly to Standard Hobby Servos
come from the power feed leads and or directly from the
brushes Usually proper lead dress and board orientation
coupled with a good filter network ( see Figure 16 ) will elimi-
nate any problems In particularly stubborn cases of motor
interference the digital channels may experience more ob-
jectionable interference than the analog channels This is
generally not because the digital channels are more suscep-
tible but rather because the type of load they typically drive
(i e a horn) will make more of a nuisance of itself than a
typical analog load (i e a steering servo) when subjected to
interference
Straightforward time integration of the digital channel out-
puts works very well with any type or degree of motor inter-
ference The simple circuits of Figure 17 integrate over a
period of about three frames (70 ms) and have approximate-
ly equal delay either going off or coming on
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TL H 7912 – 27