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MODEL 2224-1 Technical Manual
Section 7
Ludlum Measurements, Inc. Page 7-4 January 2012
period. At full meter deflection, the low pulse period, leading edge to leading
edge, will be 166 μ s, 500 cpm = 130 μ s, 400 cpm = 104 μ s, 200 cpm = 52
μ s, 100 cpm = 26 μ s, and 0 = no pulse or +5 V. The pulses are inverted by
Q302 on the amplifier/power Supply board and then integrated by R403,
C401.
LCD Drive
U211 and U212 make up the liquid crystal display drive circuitry. The display
information is sent from the μ P to U211 and 212 via
BUS
0-3 and
ADD
0-1
data lines. When the
SELECT
line is brought low by the
μ
P, the data is
transferred and latched into the drivers until the
SELECT
line is brought low
again. The corresponding digits and segments are illuminated corresponding
to the stored count information from the
μ
P.
Audio
Alpha and/or beta audio pulse frequency is generated by the μ P and coupled
to Q202. Q202 then inverts the pulses and drives the low side of the audio
transformer T201. Front-panel
VOL
control provides the bias voltage to the
top of T210. Secondary winding of T201 is coupled to unimorph speaker via
front-panel audio jack.