[time-nuts] HP5065A digital clock update
eb at telight.com
Fri Oct 7 15:50:21 UTC 2011
Just finished rebuilding the digital clock, and all is well. The
original clock IC was still good, so the display board stayed with
minimal rework - only new interface and power system needed. Made a
number of improvements:
1. Eliminated original power/interface board and clock setting buttons.
2. Isolated clock power common from chassis so no current through front panel.
3. Added electromagnetic shield surrounding entire module. All
connections via feed-through caps.
4. Added local bypassing of LED currents at drivers and on clock IC power.
5. New power system with shunt regulator for LED power, making it a
constant current load, to isolate the large step changes in segment
and scan currents from the main supply. Also includes more filtering
and fault protection.
6. Clock setting to be handled via 1 PPS signal - sped up or stopped
according to controls to be added inside center compartment,
accessible from front panel.
7. Added "dim" mode - display still visible when operating on battery
backup mode (takes 15 mA extra).
Input power: 12 VDC (regulated), approx 320 mA constant on AC power,
40 mA on battery backup (dim), 25 mA (blank), "battery read" button
still functional for normal intensity.
1 PPS input: TTL level, high impedance, 0-100 kHz.
Mode control input: AC on = +12V, AC off/fail = 0V.
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