APF Spectrograph Electronics
Calibration Lamp Power Monitor,
EL-1384
Schematic: schematics/APF/boards/EL-1384.pdf
Page last updated: February 8, 2012
The EL-1384 is a circuit designed to monitor currents on the order of a few amperes such as those found in spectrographic source lamps. Any failure of the lamp circuit such as a broken wire or burned out lamp will cause this circuit to generate a positive 5 volt output signal.
The circuit is designed around a GMW Associates CSA-1V Hall Effect Sensor. This SOIC-8 integrated circuit produces a linear output voltage proportional to a local magnetic field. In this case the magnetic field is produced by a current loop around the IC on the EL-1384 circuit board.
The output of the CSA-1V is amplified by one stage of a LM324AM low power quad operational amplifier, and passed onto a second stage configured as a comparator. When the signal on the negative input of the comparator rises above the 0.6V reference voltage (set by diode D1), the comparator output goes to ground, indicating that current is flowing through the lamp. The signal is sent out on pin J2:7 where it sinks current in an optically isolated Galil input circuit. When the Galil circuit sees a LOW signal, it indicates that the lamp is ON.
In the absence of current, the output of the comparator rises to 3.7V, turning on the front panel LED (D2) to indicate a lamp failure, and a level-shifted (by diode D3) signal is sent to the Galil circuit. When the Galil circuit sees a HIGH signal, it indicates that the lamp is OFF.
Simplified drawing
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