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test instruments projects
BH570A
BH570A digital clock

Fig. 1 - clock circuit


BH570A power supply

Fig. 3 - power supply


BH570A - TCXO frequency standard with integrated digital clock

Fig. 4 - frequency standard with digital clock


10 MHz OCXO frequency standard with digital clock

The BH570A is high precision 10 MHz OCXO frequency standard with integrated digital clock. The instrument is built around 5 ppm TCXO and external CMOS logic circuits. Beside a standard sinewave 10 MHz output are several derived clock signals available.

Clock

Figure 1 shows the clock circuit based on PLA. The clock circuit has output to six multiplexed digits and is drived from main and secondary oscillator. The secondary oscillator (25ppm) is switched automatically on if power failure. The secondary oscillator has less power consuption, unlike its precision is only 25ppm.

Display

The clock display is build with four common cathode 0.8-inch size LEDs and two 0.4-inch size LEDs.

BH570A digital clock display

Fig. 2 - multiplexed six digits common cathode LED display


Power Supply

Figure 3 shows power supply for frequency standard, TCXO with logic and digital clock. The power supply has multiple voltage outputs, power line detector, battery switcher and battery charger and Power On Reset signal generator. The instrument is powered from external line power supply. If power supply is down, the line detector send a signal and the instrument is powered from battery. In this case, the LED display is off and main oscillator is replaced with secondary oscillator. If line is restored, the LED display is on and main oscillator is in restarted. The battery is continuously monitored and charged. The battery backup time is approx. 14 hours.

Construction

Figure 4 shows the construction. The system can be expanded (i.e. external interface, etc.), with a microcontroller through a feature connector. However, the standard test instument doesn't need a microcontroller. The instrument measures 150 x 50 x 180 mm. Power consumption is about 4 Watt. Backup battery are four NiMH cells size AA with capacity of 2.7Ah.