ML145026, ML145027, ML145028
LANSDALE Semiconductor, Inc.
Legacy Applications Information
In Figure 18, the ML145026 encoder is set to run at an os-
cillator frequency of about 4 to 9 kHz. Thus, the time required
for a complete two–word encoding sequence is about 20 to 40
ms. The data output from the encoder gates an RC oscillator
running at 50 kHz; the oscillator shown starts rapidly enough
to be used in this application. When the “send” button is not
depressed, both the ML145026 and oscillator are in a
low–power standby state. The RC oscillator has to be trimmed
for 50 kHz and has some drawbacks for frequency stability. A
superior system uses a ceramic resonator oscillator running at
400 kHz. This oscillator feeds a divider as shown in Figure 19.
The unused inputs of the MC14011UB must be grounded.
The MLED81 IRED is driven with the 50 kHz square wave
at about 200 to 300 mA to generate the carrier. If desired, two
IREDs wired in series can be used (see Application Note
AN1016 for more information). The bipolar IRED switch,
shown in Figure 18, offers two advantages over a FET. First, a
logic FET has too much gate capacitance for the MC14011UB
to drive without waveform distortion. Second, the bipolar drive
permits lower supply voltages, which are an advantage in
portable battery–powered applications.
The configuration shown in Figure 18 operates over a supply
range of 4.5 to 18 V. A low–voltage system which operates
down to 2.5 V could be realized if the oscillator section of a
MC74HC4060 is used in place of the MC14011UB. The data
output of the ML145026 is inverted and fed to the RESET pin
of the MC74HC4060. Alternately, the MC74HCU04 could be
used for the oscillator.
For information on the MC14011UB, MC74HCU04 and
MC74HC4060 consult ON Semiconductor.
The receiver in Figure 20 couples an IR–sensitive diode to
input preamp A1, followed by band–pass amplifier A2 with
again of about 10. Limiting stage A3 follows, with an output of
about 800 mV p–p. The limited 50 kHz burst is detected by
comparator A4 that passes only positive pulses, and peak–detect-
ed and filtered by a diode/RC network to extract the data enve-
lope from the burst. Comparator A5 boosts the signal to logic
levels compatible with the ML145027/28 data input. The Din
pin of these decoders is a standard CMOS high–impedance
input which must not be allowed to float. Therefore, direct cou-
pling from A5 to the decoder input is utilized.
Shielding should be used on at least A1 and A2, with good
ground and high–sensitivity circuit layout techniques applied.
For operation with supplies higher than + 5 V, limiter A4’s pos-
itive output swing needs to be limited to 3 to 5 V. This is
accomplished via adding a zener diode in the negative feed-
back path, thus avoiding excessive system noise. The biasing
resistor stack should be adjusted such that V3 is 1.25 to1.5 V.
This system works up to a range of about 10 meters. The
gains of the system may be adjusted to suit the individual
design needs. The 100 Ω resistor in the emitter of the first
2N5088 and the 1 kΩ resistor feeding A2 may be altered if dif-
ferent gain is required. In general, more gain does not nec-
essarily result in increased range. This is due to noise floor
limitations. The designer should increase transmitter power
and/or increase receiver aperature with Fresnal lensing to
greatly improve range. See Application Note AN1016 for addi-
For information on the MC34074 contact ON Semiconductor.
TRINARY SWITCH MANUFACTURERS
Midland Ross–Electronic Connector Div.
The above companies may not have the switches in a DIP.
For more information, call them or consult eem Electronic
Engineers Master Catalog or the Gold Book. Ask for SPDT
with center OFF.
Alternative: An SPST can be placed in series between a
SPDT and the Encoder or Decoder to achieve trinary action.
Lansdale cannot recommend one supplier over another and
in no way suggests that this is a complete listing of trinary
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